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doc: few corrections or typo fixing in design documentation
- Fixes spelling mistakes. - Grammatical error correction. - Wrapping the text at 80 line count..etc Signed-off-by: Humble Chirammal <hchiramm@redhat.com>
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@ -6,26 +6,26 @@ snapshot contents and then mount that volume to workloads.
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CephFS exposes snapshots as special, read-only directories of a subvolume
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located in `<subvolume>/.snap`. cephfs-csi can already provision writable
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volumes with snapshots as their data source, where snapshot contents are
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cloned to the newly created volume. However, cloning a snapshot to volume
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is a very expensive operation in CephFS as the data needs to be fully copied.
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When the need is to only read snapshot contents, snapshot cloning is extremely
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volumes with snapshots as their data source, where snapshot contents are cloned
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to the newly created volume. However, cloning a snapshot to volume is a very
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expensive operation in CephFS as the data needs to be fully copied. When the
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need is to only read snapshot contents, snapshot cloning is extremely
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inefficient and wasteful.
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This proposal describes a way for cephfs-csi to expose CephFS snapshots
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as shallow, read-only volumes, without needing to clone the underlying
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snapshot data.
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This proposal describes a way for cephfs-csi to expose CephFS snapshots as
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shallow, read-only volumes, without needing to clone the underlying snapshot
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data.
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## Use-cases
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What's the point of such read-only volumes?
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* **Restore snapshots selectively:** users may want to traverse snapshots,
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restoring data to a writable volume more selectively instead of restoring
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the whole snapshot.
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* **Volume backup:** users can't backup a live volume, they first need
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to snapshot it. Once a snapshot is taken, it still can't be backed-up,
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as backup tools usually work with volumes (that are exposed as file-systems)
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restoring data to a writable volume more selectively instead of restoring the
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whole snapshot.
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* **Volume backup:** users can't backup a live volume, they first need to
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snapshot it. Once a snapshot is taken, it still can't be backed-up, as backup
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tools usually work with volumes (that are exposed as file-systems)
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and not snapshots (which might have backend-specific format). What this means
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is that in order to create a snapshot backup, users have to clone snapshot
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data twice:
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@ -37,19 +37,18 @@ What's the point of such read-only volumes?
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The temporary backed-up volume will most likely be thrown away after the
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backup transfer is finished. That's a lot of wasted work for what we
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originally wanted to do! Having the ability to create volumes from
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snapshots cheaply would be a big improvement for this use case.
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originally wanted to do! Having the ability to create volumes from snapshots
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cheaply would be a big improvement for this use case.
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## Alternatives
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* _Snapshots are stored in `<subvolume>/.snap`. Users could simply visit this
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directory by themselves._
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`.snap` is CephFS-specific detail of how snapshots are exposed.
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Users / tools may not be aware of this special directory, or it may not fit
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their workflow. At the moment, the idiomatic way of accessing snapshot
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contents in CSI drivers is by creating a new volume and populating it
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with snapshot.
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`.snap` is CephFS-specific detail of how snapshots are exposed. Users / tools
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may not be aware of this special directory, or it may not fit their workflow.
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At the moment, the idiomatic way of accessing snapshot contents in CSI drivers
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is by creating a new volume and populating it with snapshot.
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## Design
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@ -57,21 +56,21 @@ Key points:
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* Volume source is a snapshot, volume access mode is `*_READER_ONLY`.
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* No actual new subvolumes are created in CephFS.
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* The resulting volume is a reference to the source subvolume snapshot.
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This reference would be stored in `Volume.volume_context` map. In order
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to reference a snapshot, we need subvol name and snapshot name.
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* Mounting such volume means mounting the respective CephFS subvolume
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and exposing the snapshot to workloads.
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* Let's call a *shallow read-only volume with a subvolume snapshot
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as its data source* just a *shallow volume* from here on out for brevity.
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* The resulting volume is a reference to the source subvolume snapshot. This
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reference would be stored in `Volume.volume_context` map. In order to
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reference a snapshot, we need subvol name and snapshot name.
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* Mounting such volume means mounting the respective CephFS subvolume and
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exposing the snapshot to workloads.
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* Let's call a *shallow read-only volume with a subvolume snapshot as its data
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source* just a *shallow volume* from here on out for brevity.
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### Controller operations
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Care must be taken when handling life-times of relevant storage resources.
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When a shallow volume is created, what would happen if:
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Care must be taken when handling life-times of relevant storage resources. When
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a shallow volume is created, what would happen if:
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* _Parent subvolume of the snapshot is removed while the shallow volume
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still exists?_
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* _Parent subvolume of the snapshot is removed while the shallow volume still
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exists?_
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This shouldn't be a problem already. The parent volume has either
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`snapshot-retention` subvol feature in which case its snapshots remain
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@ -80,8 +79,8 @@ When a shallow volume is created, what would happen if:
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* _Source snapshot from which the shallow volume originates is removed while
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that shallow volume still exists?_
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We need to make sure this doesn't happen and some book-keeping
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is necessary. Ideally we could employ some kind of reference counting.
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We need to make sure this doesn't happen and some book-keeping is necessary.
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Ideally we could employ some kind of reference counting.
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#### Reference counting for shallow volumes
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@ -92,11 +91,11 @@ When creating a volume snapshot, a reference tracker (RT), represented by a
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RADOS object, would be created for that snapshot. It would store information
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required to track the references for the backing subvolume snapshot. Upon a
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`CreateSnapshot` call, the reference tracker (RT) would be initialized with a
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single reference record, where the CSI snapshot itself is the first reference
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to the backing snapshot. Each subsequent shallow volume creation would add a
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new reference record to the RT object. Each shallow volume deletion would
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remove that reference from the RT object. Calling `DeleteSnapshot` would remove
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the reference record that was previously added in `CreateSnapshot`.
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single reference record, where the CSI snapshot itself is the first reference to
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the backing snapshot. Each subsequent shallow volume creation would add a new
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reference record to the RT object. Each shallow volume deletion would remove
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that reference from the RT object. Calling `DeleteSnapshot` would remove the
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reference record that was previously added in `CreateSnapshot`.
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The subvolume snapshot would be removed from the Ceph cluster only once the RT
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object holds no references. Note that this behavior would permit calling
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@ -110,8 +109,8 @@ object holds no references. Note that this behavior would permit calling
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* RT holds no references: delete the backing snapshot too.
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* RT holds at least one reference: keep the backing snapshot.
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To enable creating shallow volumes from snapshots that were provisioned by
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older versions of cephfs-csi (i.e. before this feature is introduced),
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To enable creating shallow volumes from snapshots that were provisioned by older
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versions of cephfs-csi (i.e. before this feature is introduced),
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`CreateVolume` for shallow volumes would also create an RT object in case it's
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missing. It would be initialized to two: the source snapshot and the newly
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created shallow volume.
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@ -141,17 +140,17 @@ Things to look out for:
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It doesn't consume any space on the filesystem. `Volume.capacity_bytes` is
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allowed to contain zero. We could use that.
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* _What should be the requested size when creating the volume (specified e.g.
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in PVC)?_
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* _What should be the requested size when creating the volume (specified e.g. in
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PVC)?_
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This one is tricky. CSI spec allows for
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`CreateVolumeRequest.capacity_range.{required_bytes,limit_bytes}` to be
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zero. On the other hand,
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`PersistentVolumeClaim.spec.resources.requests.storage` must be bigger
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than zero. cephfs-csi doesn't care about the requested size (the volume
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will be read-only, so it has no usable capacity) and would always set it
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to zero. This shouldn't case any problems for the time being, but still
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is something we should keep in mind.
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`CreateVolumeRequest.capacity_range.{required_bytes,limit_bytes}` to be zero.
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On the other hand,
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`PersistentVolumeClaim.spec.resources.requests.storage` must be bigger than
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zero. cephfs-csi doesn't care about the requested size (the volume will be
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read-only, so it has no usable capacity) and would always set it to zero. This
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shouldn't case any problems for the time being, but still is something we
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should keep in mind.
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`CreateVolume` and behavior when using volume as volume source (PVC-PVC clone):
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@ -167,8 +166,8 @@ Volume deletion is trivial.
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### `CreateSnapshot`
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Snapshotting read-only volumes doesn't make sense in general, and should
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be rejected.
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Snapshotting read-only volumes doesn't make sense in general, and should be
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rejected.
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### `ControllerExpandVolume`
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@ -194,8 +193,8 @@ whole subvolume first, and only then perform the binds to target paths.
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#### For case (a)
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Subvolume paths are normally retrieved by
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`ceph fs subvolume info/getpath <VOLUME NAME> <SUBVOLUME NAME> <SUBVOLUMEGROUP NAME>`,
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which outputs a path like so:
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`ceph fs subvolume info/getpath <VOLUME NAME> <SUBVOLUME NAME> <SUBVOLUMEGROUP NAME>`
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, which outputs a path like so:
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```
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/volumes/<VOLUME NAME>/<SUBVOLUME NAME>/<UUID>
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@ -217,12 +216,12 @@ itself still exists or not.
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#### For case (b)
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For cases where subvolumes are managed externally and not by cephfs-csi, we
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must assume that the cephx user we're given can access only
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For cases where subvolumes are managed externally and not by cephfs-csi, we must
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assume that the cephx user we're given can access only
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`/volumes/<VOLUME NAME>/<SUBVOLUME NAME>/<UUID>` so users won't be able to
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benefit from snapshot retention. Users will need to be careful not to delete
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the parent subvolumes and snapshots while they are associated by these shallow
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RO volumes.
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benefit from snapshot retention. Users will need to be careful not to delete the
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parent subvolumes and snapshots while they are associated by these shallow RO
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volumes.
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### `NodePublishVolume`, `NodeUnpublishVolume`
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@ -235,27 +234,27 @@ mount.
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## Volume parameters, volume context
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This section provides a discussion around determinig what volume parameters and
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This section provides a discussion around determining what volume parameters and
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volume context parameters will be used to convey necessary information to the
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cephfs-csi driver in order to support shallow volumes.
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Volume parameters `CreateVolumeRequest.parameters`:
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* Should be "shallow" the default mode for all `CreateVolume` calls that have
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(a) snapshot as data source and (b) read-only volume access mode? If not,
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a new volume parameter should be introduced: e.g `isShallow: <bool>`. On the
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(a) snapshot as data source and (b) read-only volume access mode? If not, a
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new volume parameter should be introduced: e.g `isShallow: <bool>`. On the
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other hand, does it even makes sense for users to want to create full copies
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of snapshots and still have them read-only?
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Volume context `Volume.volume_context`:
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* Here we definitely need `isShallow` or similar. Without it we wouldn't be
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able to distinguish between a regular volume that just happens to have
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a read-only access mode, and a volume that references a snapshot.
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* Here we definitely need `isShallow` or similar. Without it we wouldn't be able
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to distinguish between a regular volume that just happens to have a read-only
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access mode, and a volume that references a snapshot.
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* Currently cephfs-csi recognizes `subvolumePath` for dynamically provisioned
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volumes and `rootPath` for pre-previsioned volumes. As mentioned in
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[`NodeStageVolume`, `NodeUnstageVolume` section](#NodeStageVolume-NodeUnstageVolume),
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snapshots cannot be mounted directly. How do we pass in path to the parent
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[`NodeStageVolume`, `NodeUnstageVolume` section](#NodeStageVolume-NodeUnstageVolume)
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, snapshots cannot be mounted directly. How do we pass in path to the parent
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subvolume?
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* a) Path to the snapshot is passed in via `subvolumePath` / `rootPath`,
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e.g.
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@ -1,7 +1,7 @@
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# Design to handle clusterID and poolID for DR
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During disaster recovery/migration of a cluster, as part of the failover, the
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kubernetes artifacts like deployment, PVC, PV, etc will be restored to a new
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kubernetes artifacts like deployment, PVC, PV, etc. will be restored to a new
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cluster by the admin. Even if the kubernetes objects are restored the
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corresponding RBD/CephFS subvolume cannot be retrieved during CSI operations as
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the clusterID and poolID are not the same in both clusters. Let's see the
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@ -10,8 +10,8 @@ problem in more detail below.
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`0001-0009-rook-ceph-0000000000000002-b0285c97-a0ce-11eb-8c66-0242ac110002`
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The above is the sample volumeID sent back in response to the CreateVolume
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operation and added as a volumeHandle in the PV spec. CO (Kubernetes) uses
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above as the identifier for other operations on the volume/PVC.
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operation and added as a volumeHandle in the PV spec. CO (Kubernetes) uses above
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as the identifier for other operations on the volume/PVC.
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The VolumeID is encoded as,
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@ -33,7 +33,7 @@ the other cluster.
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During the Disaster Recovery (failover operation) the PVC and PV will be
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recreated on the other cluster. When Ceph-CSI receives the request for
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operations like (NodeStage, ExpandVolume, DeleteVolume, etc) the volumeID is
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operations like (NodeStage, ExpandVolume, DeleteVolume, etc.) the volumeID is
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sent in the request which will help to identify the volume.
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```yaml=
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@ -68,15 +68,15 @@ metadata:
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```
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During CSI/Replication operations, Ceph-CSI will decode the volumeID and gets
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the monitor configuration from the configmap and by the poolID will get the
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pool Name and retrieves the OMAP data stored in the rados OMAP and finally
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check the volume is present in the pool.
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the monitor configuration from the configmap and by the poolID will get the pool
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Name and retrieves the OMAP data stored in the rados OMAP and finally check the
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volume is present in the pool.
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## Problems with volumeID Replication
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* The clusterID can be different
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* as the clusterID is the namespace where rook is deployed, the Rook might be
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deployed in the different namespace on a secondary cluster
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* as the clusterID is the namespace where rook is deployed, the Rook might
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be deployed in the different namespace on a secondary cluster
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* In standalone Ceph-CSI the clusterID is fsID and fsID is unique per
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cluster
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@ -124,8 +124,8 @@ metadata:
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name: ceph-csi-config
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```
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**Note:-** the configmap will be mounted as a volume to the CSI (provisioner
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and node plugin) pods.
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**Note:-** the configmap will be mounted as a volume to the CSI (provisioner and
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node plugin) pods.
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The above configmap will get created as it is or updated (if new Pools are
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created on the existing cluster) with new entries when the admin choose to
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@ -149,18 +149,18 @@ Replicapool with ID `1` on site1 and Replicapool with ID `2` on site2.
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After getting the required mapping Ceph-CSI has the required information to get
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more details from the rados OMAP. If we have multiple clusterID mapping it will
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loop through all the mapping and checks the corresponding pool to get the OMAP
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data. If the clusterID mapping does not exist Ceph-CSI will return a `Not
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Found` error message to the caller.
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data. If the clusterID mapping does not exist Ceph-CSI will return a `Not Found`
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error message to the caller.
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After failover to the cluster `site2-storage`, the admin might have created new
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PVCs on the primary cluster `site2-storage`. Later after recovering the
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cluster `site1-storage`, the admin might choose to failback from
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`site2-storage` to `site1-storage`. Now admin needs to copy all the newly
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created kubernetes artifacts to the failback cluster. For clusterID mapping, the
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admin needs to copy the above-created configmap `ceph-clusterid-mapping` to
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the failback cluster. When Ceph-CSI receives a CSI/Replication request for
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the volumes created on the `site2-storage` it will decode the volumeID and
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retrieves the clusterID ie `site2-storage`. In the above configmap
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admin needs to copy the above-created configmap `ceph-clusterid-mapping` to the
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failback cluster. When Ceph-CSI receives a CSI/Replication request for the
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volumes created on the `site2-storage` it will decode the volumeID and retrieves
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the clusterID ie `site2-storage`. In the above configmap
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`ceph-clusterid-mapping` the `site2-storage` is the value and `site1-storage`
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is the key in the `clusterIDMapping` entry.
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@ -169,8 +169,8 @@ is found in `key` it will consider `value` as the corresponding mapping, if it
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is found in `value` place it will treat `key` as the corresponding mapping and
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retrieves all the poolID details of the cluster.
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This mapping on the remote cluster is only required when we are doing a
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failover operation from the primary cluster to a remote cluster. The existing
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volumes that are created on the remote cluster does not require
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any mapping as the volumeHandle already contains the required information about
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the local cluster (clusterID, poolID etc).
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This mapping on the remote cluster is only required when we are doing a failover
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operation from the primary cluster to a remote cluster. The existing volumes
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that are created on the remote cluster does not require any mapping as the
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volumeHandle already contains the required information about the local cluster (
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clusterID, poolID etc).
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@ -16,7 +16,7 @@ Some but not all the benefits of this approach:
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* volume encryption: encryption of a volume attached by rbd
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* encryption at rest: encryption of physical disk done by ceph
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* LUKS: Linux Unified Key Setup: stores all of the needed setup information for
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* LUKS: Linux Unified Key Setup: stores all the needed setup information for
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dm-crypt on the disk
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* dm-crypt: linux kernel device-mapper crypto target
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* cryptsetup: the command line tool to interface with dm-crypt
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@ -28,8 +28,8 @@ requirement by using dm-crypt module through cryptsetup cli interface.
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### Implementation Summary
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* Encryption is implemented using cryptsetup with LUKS extension.
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A good introduction to LUKS and dm-crypt in general can be found
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* Encryption is implemented using cryptsetup with LUKS extension. A good
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introduction to LUKS and dm-crypt in general can be found
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[here](https://wiki.archlinux.org/index.php/Dm-crypt/Device_encryption#Encrypting_devices_with_cryptsetup)
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Functions to implement necessary interaction are implemented in a separate
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`cryptsetup.go` file.
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@ -45,8 +45,8 @@ requirement by using dm-crypt module through cryptsetup cli interface.
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volume attach request
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* `NodeStageVolume`: refactored to open encrypted device (`openEncryptedDevice`)
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* `openEncryptedDevice`: looks up for a passphrase matching the volume id,
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returns the new device path in the form: `/dev/mapper/luks-<volume_id>`.
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On the woker node where the attach is scheduled:
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returns the new device path in the form: `/dev/mapper/luks-<volume_id>`. On
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the worker node where the attach is scheduled:
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```shell
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$ lsblk
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@ -63,7 +63,7 @@ requirement by using dm-crypt module through cryptsetup cli interface.
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* StorageClass extended with following parameters:
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1. `encrypted` ("true" or "false")
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1. `encryptionKMSID` (string representing kms configuration of choice)
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2. `encryptionKMSID` (string representing kms configuration of choice)
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ceph-csi plugin may support different kms vendors with different type of
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authentication
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@ -133,14 +133,19 @@ metadata:
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The main components that are used to support encrypted volumes:
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1. the `EncryptionKMS` interface
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* an instance is configured per volume object (`rbdVolume.KMS`)
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* used to authenticate with a master key or token
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* can store the KEK (Key-Encryption-Key) for encrypting and decrypting the
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DEKs (Data-Encryption-Key)
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|
||||
1. the `DEKStore` interface
|
||||
|
||||
* saves and fetches the DEK (Data-Encryption-Key)
|
||||
* can be provided by a KMS, or by other components (like `rbdVolume`)
|
||||
|
||||
1. the `VolumeEncryption` type
|
||||
|
||||
* combines `EncryptionKMS` and `DEKStore` into a single place
|
||||
* easy to configure from other components or subsystems
|
||||
* provides a simple API for all KMS operations
|
||||
|
||||
@ -14,7 +14,8 @@ KMS implementation. Or, if changes would be minimal, a configuration option to
|
||||
one of the implementations can be added.
|
||||
|
||||
Different KMS implementations and their configurable options can be found at
|
||||
[`csi-kms-connection-details.yaml`](../../../examples/kms/vault/csi-kms-connection-details.yaml).
|
||||
[`csi-kms-connection-details.yaml`](../../../examples/kms/vault/csi-kms-connection-details.yaml)
|
||||
.
|
||||
|
||||
### VaultTokensKMS
|
||||
|
||||
@ -26,7 +27,8 @@ An example of the per Tenant configuration options are in
|
||||
[`tenant-config.yaml`](../../../examples/kms/vault/tenant-config.yaml) and
|
||||
[`tenant-token.yaml`](../../../examples/kms/vault/tenant-token.yaml).
|
||||
|
||||
Implementation is in [`vault_tokens.go`](../../../internal/util/vault_tokens.go).
|
||||
Implementation is in [`vault_tokens.go`](../../../internal/util/vault_tokens.go)
|
||||
.
|
||||
|
||||
### Vault
|
||||
|
||||
@ -36,7 +38,7 @@ Implementation is in [`vault.go`](../../../internal/util/vault.go).
|
||||
|
||||
## Extension or New KMS implementation
|
||||
|
||||
Normally ServiceAccounts are provided by Kubernetes in the containers
|
||||
Normally ServiceAccounts are provided by Kubernetes in the containers'
|
||||
filesystem. This only allows a single ServiceAccount and is static for the
|
||||
lifetime of the Pod. Ceph-CSI runs in the namespace of the storage
|
||||
administrator, and has access to the single ServiceAccount linked in the
|
||||
@ -53,7 +55,7 @@ steps need to be taken:
|
||||
replace the default (`AuthKubernetesTokenPath:
|
||||
/var/run/secrets/kubernetes.io/serviceaccount/token`)
|
||||
|
||||
Currently the Ceph-CSI components may read Secrets and ConfigMaps from the
|
||||
Currently, the Ceph-CSI components may read Secrets and ConfigMaps from the
|
||||
Tenants namespace. These permissions need to be extended to allow Ceph-CSI to
|
||||
read the contents of the ServiceAccount(s) in the Tenants namespace.
|
||||
|
||||
@ -61,7 +63,8 @@ read the contents of the ServiceAccount(s) in the Tenants namespace.
|
||||
|
||||
### Global Configuration
|
||||
|
||||
1. a StorageClass links to a KMS configuration by providing the `kmsID` parameter
|
||||
1. a StorageClass links to a KMS configuration by providing the `kmsID`
|
||||
parameter
|
||||
1. a ConfigMap in the namespace of the Ceph-CSI deployment contains the KMS
|
||||
configuration for the `kmsID`
|
||||
([`csi-kms-connection-details.yaml`](../../../examples/kms/vault/csi-kms-connection-details.yaml))
|
||||
@ -76,8 +79,8 @@ configuration from the ConfigMap.
|
||||
1. needs ServiceAccount with a known name with permissions to connect to Vault
|
||||
1. optional ConfigMap with options for Vault that override default settings
|
||||
|
||||
A `CreateVolume` request contains the owner (Namespace) of the Volume.
|
||||
The KMS configuration indicates that additional attributes need to be fetched
|
||||
from the Tenants namespace, so the provisioner will fetch these. The additional
|
||||
configuration and ServiceAccount are merged in the provisioners configuration
|
||||
A `CreateVolume` request contains the owner (Namespace) of the Volume. The KMS
|
||||
configuration indicates that additional attributes need to be fetched from the
|
||||
Tenants namespace, so the provisioner will fetch these. The additional
|
||||
configuration and ServiceAccount are merged in the provisioners' configuration
|
||||
for the KMS-implementation while creating the volume.
|
||||
|
||||
@ -1,11 +1,11 @@
|
||||
# RBD MIRRORING
|
||||
|
||||
RBD mirroring is a process of replication of RBD images between two or more
|
||||
Ceph clusters. Mirroring ensures point-in-time, crash-consistent RBD images
|
||||
between clusters, RBD mirroring is mainly used for disaster recovery (i.e.
|
||||
having a secondary site as a failover). See [Ceph
|
||||
documentation](https://docs.ceph.com/en/latest/rbd/rbd-mirroring) on RBD
|
||||
mirroring for complete information.
|
||||
RBD mirroring is a process of replication of RBD images between two or more Ceph
|
||||
clusters. Mirroring ensures point-in-time, crash-consistent RBD images between
|
||||
clusters, RBD mirroring is mainly used for disaster recovery (i.e. having a
|
||||
secondary site as a failover).
|
||||
See [Ceph documentation](https://docs.ceph.com/en/latest/rbd/rbd-mirroring) on
|
||||
RBD mirroring for complete information.
|
||||
|
||||
## Architecture
|
||||
|
||||
@ -28,8 +28,8 @@ PersistentVolumeClaim (PVC) on the secondary site during the failover.
|
||||
VolumeHandle to identify the OMAP data nor the image anymore because as we have
|
||||
only PoolID and ClusterID in the VolumeHandle. We cannot identify the correct
|
||||
pool name from the PoolID because pool name will remain the same on both
|
||||
clusters but not the PoolID even the ClusterID can be different on the
|
||||
secondary cluster.
|
||||
clusters but not the PoolID even the ClusterID can be different on the secondary
|
||||
cluster.
|
||||
|
||||
> Sample PV spec which will be used by rbdplugin controller to regenerate OMAP
|
||||
> data
|
||||
@ -56,10 +56,10 @@ csi:
|
||||
```
|
||||
|
||||
> **VolumeHandle** is the unique volume name returned by the CSI volume plugin’s
|
||||
CreateVolume to refer to the volume on all subsequent calls.
|
||||
> CreateVolume to refer to the volume on all subsequent calls.
|
||||
|
||||
Once the static PVC is created on the secondary cluster, the Kubernetes User
|
||||
can try delete the PVC,expand the PVC or mount the PVC. In case of mounting
|
||||
Once the static PVC is created on the secondary cluster, the Kubernetes User can
|
||||
try to delete the PVC,expand the PVC or mount the PVC. In case of mounting
|
||||
(NodeStageVolume) we will get the volume context in RPC call but not in the
|
||||
Delete/Expand Request. In Delete/Expand RPC request only the VolumeHandle
|
||||
(`clusterID-poolID-volumeuniqueID`) will be sent where it contains the encoded
|
||||
@ -73,17 +73,17 @@ secondary cluster as the PoolID and ClusterID always may not be the same.
|
||||
|
||||
To solve this problem, We will have a new controller(rbdplugin controller)
|
||||
running as part of provisioner pod which watches for the PV objects. When a PV
|
||||
is created it will extract the required information from the PV spec and it
|
||||
is created it will extract the required information from the PV spec, and it
|
||||
will regenerate the OMAP data. Whenever Ceph-CSI gets a RPC request with older
|
||||
VolumeHandle, it will check if any new VolumeHandle exists for the old
|
||||
VolumeHandle. If yes, it uses the new VolumeHandle for internal operations (to
|
||||
get pool name, Ceph monitor details from the ClusterID etc).
|
||||
|
||||
Currently, We are making use of watchers in node stage request to make sure
|
||||
ReadWriteOnce (RWO) PVC is mounted on a single node at a given point in time.
|
||||
We need to change the watchers logic in the node stage request as when we
|
||||
enable the RBD mirroring on an image, a watcher will be added on a RBD image by
|
||||
the rbd mirroring daemon.
|
||||
ReadWriteOnce (RWO) PVC is mounted on a single node at a given point in time. We
|
||||
need to change the watchers logic in the node stage request as when we enable
|
||||
the RBD mirroring on an image, a watcher will be added on a RBD image by the rbd
|
||||
mirroring daemon.
|
||||
|
||||
To solve the ClusterID problem, If the ClusterID is different on the second
|
||||
cluster, the admin has to create a new ConfigMap for the mapped ClusterID's.
|
||||
|
||||
@ -9,51 +9,49 @@
|
||||
|
||||
## Rbd nbd
|
||||
|
||||
The rbd CSI plugin will provision new rbd images and attach and mount those
|
||||
to workloads. Currently, the default mounter is krbd, which uses the kernel
|
||||
rbd driver to mount the rbd images onto the application pod. Here on
|
||||
at Ceph-CSI we will also have a userspace way of mounting the rbd images,
|
||||
via rbd-nbd.
|
||||
The rbd CSI plugin will provision new rbd images and attach and mount those to
|
||||
workloads. Currently, the default mounter is krbd, which uses the kernel rbd
|
||||
driver to mount the rbd images onto the application pod. Here on at Ceph-CSI we
|
||||
will also have a userspace way of mounting the rbd images, via rbd-nbd.
|
||||
|
||||
[Rbd-nbd](https://docs.ceph.com/en/latest/man/8/rbd-nbd/) is a client for
|
||||
RADOS block device (rbd) images like the existing rbd kernel module. It
|
||||
will map an rbd image to an nbd (Network Block Device) device, allowing
|
||||
access to it as a regular local block device.
|
||||
[Rbd-nbd](https://docs.ceph.com/en/latest/man/8/rbd-nbd/) is a client for RADOS
|
||||
block device (rbd) images like the existing rbd kernel module. It will map an
|
||||
rbd image to an nbd (Network Block Device) device, allowing access to it as a
|
||||
regular local block device.
|
||||
|
||||
|
||||
|
||||
It’s worth making a note that the rbd-nbd processes will run on the
|
||||
client-side, which is inside the `csi-rbdplugin` node plugin.
|
||||
It’s worth making a note that the rbd-nbd processes will run on the client-side,
|
||||
which is inside the `csi-rbdplugin` node plugin.
|
||||
|
||||
### Advantages of userspace mounters
|
||||
|
||||
- It is easier to add features to rbd-nbd as it is released regularly with
|
||||
Ceph, and more difficult and time consuming to add features to the kernel
|
||||
rbd module as that is part of the Linux kernel release schedule.
|
||||
- Container upgrades will be independent of the host node, which means if
|
||||
there are any new features with rbd-nbd, we don’t have to reboot the node
|
||||
as the changes will be shipped inside the container.
|
||||
- Because the container upgrades are host node independent, we will be a
|
||||
better citizen in K8s by switching to the userspace model.
|
||||
- It is easier to add features to rbd-nbd as it is released regularly with Ceph,
|
||||
and more difficult and time consuming to add features to the kernel rbd module
|
||||
as that is part of the Linux kernel release schedule.
|
||||
- Container upgrades will be independent of the host node, which means if there
|
||||
are any new features with rbd-nbd, we don’t have to reboot the node as the
|
||||
changes will be shipped inside the container.
|
||||
- Because the container upgrades are host node independent, we will be a better
|
||||
citizen in K8s by switching to the userspace model.
|
||||
- Unlike krbd, rbd-nbd uses librbd user-space library that gets most of the
|
||||
development focus, and hence rbd-nbd will be feature-rich.
|
||||
- Being entirely kernel space impacts fault-tolerance as any kernel panic
|
||||
affects a whole node not only a single pod that is using rbd storage.
|
||||
Thanks to the rbd-nbd’s userspace design, we are less bothered here, the
|
||||
krbd is a complete kernel and vendor-specific driver which needs changes
|
||||
on every feature basis, on the other hand, rbd-nbd depends on NBD generic
|
||||
driver, while all the vendor-specific logic sits in the userspace. It's
|
||||
worth taking note that NBD generic driver is mostly unchanged much from
|
||||
years and consider it to be much stable. Also given NBD is a generic
|
||||
driver there will be many eyes on it compared to the rbd driver.
|
||||
affects a whole node not only a single pod that is using rbd storage. Thanks
|
||||
to the rbd-nbd’s userspace design, we are less bothered here, the krbd is a
|
||||
complete kernel and vendor-specific driver which needs changes on every
|
||||
feature basis, on the other hand, rbd-nbd depends on NBD generic driver, while
|
||||
all the vendor-specific logic sits in the userspace. It's worth taking note
|
||||
that NBD generic driver is mostly unchanged much from years and consider it to
|
||||
be much stable. Also given NBD is a generic driver there will be many eyes on
|
||||
it compared to the rbd driver.
|
||||
|
||||
### Side effects of userspace mounters
|
||||
|
||||
Since the rbd-nbd processes run per volume map on the client side i.e.
|
||||
inside the `csi-rbdplugin` node plugin, a restart of the node plugin will
|
||||
terminate all the rbd-nbd processes, and there is no way to restore
|
||||
these processes back to life currently, which could lead to IO errors
|
||||
on all the application pods.
|
||||
Since the rbd-nbd processes run per volume map on the client side i.e. inside
|
||||
the `csi-rbdplugin` node plugin, a restart of the node plugin will terminate all
|
||||
the rbd-nbd processes, and there is no way to restore these processes back to
|
||||
life currently, which could lead to IO errors on all the application pods.
|
||||
|
||||
|
||||
|
||||
@ -61,42 +59,42 @@ This is where the Volume healer could help.
|
||||
|
||||
## Volume healer
|
||||
|
||||
Volume healer runs on the start of rbd node plugin and runs within the
|
||||
node plugin driver context.
|
||||
Volume healer runs on the start of rbd node plugin and runs within the node
|
||||
plugin driver context.
|
||||
|
||||
Volume healer does the below,
|
||||
|
||||
- Get the Volume attachment list for the current node where it is running
|
||||
- Filter the volume attachments list through matching driver name and
|
||||
status attached
|
||||
- For each volume attachment get the respective PV information and check
|
||||
the criteria of PV Bound, mounter type
|
||||
- Build the StagingPath where rbd images PVC is mounted, based on the
|
||||
KUBELET path and PV object
|
||||
- Filter the volume attachments list through matching driver name and status
|
||||
attached
|
||||
- For each volume attachment get the respective PV information and check the
|
||||
criteria of PV Bound, mounter type
|
||||
- Build the StagingPath where rbd images PVC is mounted, based on the KUBELET
|
||||
path and PV object
|
||||
- Construct the NodeStageVolume() request and send Request to CSI Driver.
|
||||
- The NodeStageVolume() has a way to identify calls received from the
|
||||
healer and when executed from the healer context, it just runs in the
|
||||
minimal required form, where it fetches the previously mapped device to
|
||||
the image, and the respective secrets and finally ensures to bringup the
|
||||
respective process back to life. Thus enabling IO to continue.
|
||||
- The NodeStageVolume() has a way to identify calls received from the healer and
|
||||
when executed from the healer context, it just runs in the minimal required
|
||||
form, where it fetches the previously mapped device to the image, and the
|
||||
respective secrets and finally ensures to bringup the respective process back
|
||||
to life. Thus enabling IO to continue.
|
||||
|
||||
### More thoughts
|
||||
|
||||
- Currently the NodeStageVolume() call is safeguarded by the global Ceph-CSI
|
||||
level lock (per volID) that needs to be acquired before doing any of the
|
||||
NodeStage, NodeUnstage, NodePublish, NodeUnPulish operations. Hence none
|
||||
of the operations happen in parallel.
|
||||
NodeStage, NodeUnstage, NodePublish, NodeUnPublish operations. Hence none of
|
||||
the operations happen in parallel.
|
||||
- Any issues if the NodeUnstage is issued by kubelet?
|
||||
- This can not be a problem as we take a lock at the Ceph-CSI level
|
||||
- If the NodeUnstage success, Ceph-CSI will return StagingPath not found
|
||||
error, we can then skip
|
||||
- If the NodeUnstage fails with an operation already going on, in the
|
||||
next NodeUnstage the volume gets unmounted
|
||||
- If the NodeUnstage fails with an operation already going on, in the next
|
||||
NodeUnstage the volume gets unmounted
|
||||
- What if the PVC is deleted?
|
||||
- If the PVC is deleted, the volume attachment list might already got
|
||||
- If the PVC is deleted, the volume attachment list might already get
|
||||
refreshed and entry will be skipped/deleted at the healer.
|
||||
- For any reason, If the request bails out with Error NotFound, skip the
|
||||
PVC, assuming it might have deleted or the NodeUnstage might have
|
||||
already happened.
|
||||
PVC, assuming it might have deleted or the NodeUnstage might have already
|
||||
happened.
|
||||
- The Volume healer currently works with rbd-nbd, but the design can
|
||||
accommodate other userspace mounters (may be ceph-fuse).
|
||||
Loading…
Reference in New Issue
Block a user