mirror of
https://github.com/ceph/ceph-csi.git
synced 2024-11-15 02:40:23 +00:00
7c0ce53eeb
Add design doc for QoS for rbd devices mapped with both krbd and rbd-nbd closes: #521 Signed-off-by: Madhu Rajanna <madhupr007@gmail.com>
272 lines
10 KiB
Markdown
272 lines
10 KiB
Markdown
# Design Doc for RBD QoS using cgroup v2
|
|
|
|
## Introduction
|
|
|
|
The RBD QoS (Quality of Service) design aims to address the issue of IO noisy
|
|
neighbor problems encountered in early Ceph deployments catering to OpenStack
|
|
environments. These problems were effectively managed by implementing QEMU
|
|
throttling at the virtio-blk/scsi level. To further enhance this,
|
|
capacity-based IOPS were introduced, providing a more dynamic experience
|
|
similar to public cloud environments.
|
|
|
|
The challenge arises in virtual environments, where a noisy neighbor can lead
|
|
to performance degradation for other instances sharing the same resources.
|
|
Although it's uncommon to observe noisy neighbor issues in Kubernetes
|
|
environments backed by Ceph storage, the possibility exists. The existing QoS
|
|
support with rbd-nbd doesn't apply to krbd, and as rbd-nbd isn't suitable for
|
|
container production workloads, a solution is needed for krbd.
|
|
|
|
To mitigate resource starvation issues, setting QoS at the device level through
|
|
cgroup v2 when enabled becomes crucial. This approach guarantees that I/O
|
|
capacity isn't overcommitted and is fairly distributed among workloads.
|
|
|
|
## Dependency
|
|
|
|
* cgroup v2 must be enabled on the Node
|
|
* We might have Kubernetes dependency as well
|
|
* Container runtime dependency that supports cgroupv2
|
|
|
|
## Manual steps for implementing RBD QoS in a Kubernetes Cluster
|
|
|
|
```bash
|
|
[$] ssh root@node1
|
|
sh-4.4# chroot /host
|
|
sh-5.1# cat /proc/partitions
|
|
major minor #blocks name
|
|
|
|
259 0 125829120 nvme0n1
|
|
259 1 1024 nvme0n1p1
|
|
259 2 130048 nvme0n1p2
|
|
259 3 393216 nvme0n1p3
|
|
259 4 125303791 nvme0n1p4
|
|
259 6 52428800 nvme2n1
|
|
7 0 536870912 loop0
|
|
259 5 536870912 nvme1n1
|
|
252 0 52428800 rbd0
|
|
sh-5.1#
|
|
```
|
|
|
|
Once the rbd device is mapped on the node we get the device's major and minor
|
|
number we need to set the io limit on the device but we need to find the right
|
|
cgroup file where we need to set the limit
|
|
|
|
Kubernetes/Openshift creates a custom cgroup hierarchy for the pods it created
|
|
but start is `/sys/fs/cgroup` folder
|
|
|
|
```bash
|
|
sh-5.1# cd /sys/fs/cgroup/
|
|
sh-5.1# ls
|
|
cgroup.controllers cgroup.subtree_control cpuset.mems.effective io.stat memory.reclaim sys-kernel-debug.mount
|
|
cgroup.max.depth cgroup.threads dev-hugepages.mount kubepods.slice memory.stat sys-kernel-tracing.mount
|
|
cgroup.max.descendants cpu.pressure dev-mqueue.mount machine.slice misc.capacity system.slice
|
|
cgroup.procs cpu.stat init.scope memory.numa_stat sys-fs-fuse-connections.mount user.slice
|
|
cgroup.stat cpuset.cpus.effective io.pressure memory.pressure sys-kernel-config.mount
|
|
```
|
|
|
|
`kubepods.slice` is the starting point and it contains multiple slices
|
|
|
|
```bash
|
|
sh-5.1# cd kubepods.slice
|
|
sh-5.1# ls
|
|
cgroup.controllers cpuset.cpus hugetlb.2MB.rsvd.max memory.pressure
|
|
cgroup.events cpuset.cpus.effective io.bfq.weight memory.reclaim
|
|
cgroup.freeze cpuset.cpus.partition io.latency memory.stat
|
|
cgroup.kill cpuset.mems io.max memory.swap.current
|
|
cgroup.max.depth cpuset.mems.effective io.pressure memory.swap.events
|
|
cgroup.max.descendants hugetlb.1GB.current io.stat memory.swap.high
|
|
cgroup.procs hugetlb.1GB.events kubepods-besteffort.slice memory.swap.max
|
|
cgroup.stat hugetlb.1GB.events.local kubepods-burstable.slice memory.zswap.current
|
|
cgroup.subtree_control hugetlb.1GB.max kubepods-pod2b38830b_c2d6_4528_8935_b1c08511b1e3.slice memory.zswap.max
|
|
cgroup.threads hugetlb.1GB.numa_stat memory.current misc.current
|
|
cgroup.type hugetlb.1GB.rsvd.current memory.events misc.max
|
|
cpu.idle hugetlb.1GB.rsvd.max memory.events.local pids.current
|
|
cpu.max hugetlb.2MB.current memory.high pids.events
|
|
cpu.max.burst hugetlb.2MB.events memory.low pids.max
|
|
cpu.pressure hugetlb.2MB.events.local memory.max rdma.current
|
|
cpu.stat hugetlb.2MB.max memory.min rdma.max
|
|
cpu.weight hugetlb.2MB.numa_stat memory.numa_stat
|
|
cpu.weight.nice hugetlb.2MB.rsvd.current memory.oom.group
|
|
```
|
|
|
|
Based on the QoS of the pod, either our application pod will end up in the
|
|
above `kubepods-besteffort.slice` or `kubepods-burstable.slice` or
|
|
`kubepods.slice` (Guaranteed QoS) cgroup. The 3 QoS classes are defined
|
|
[here](https://kubernetes.io/docs/concepts/workloads/pods/pod-QoS/#quality-of-service-classes)
|
|
|
|
To identify the right cgroup file, we need pod UUID and container UUID from the
|
|
`pod yaml` output
|
|
|
|
```bash
|
|
[$]kubectl get po csi-rbd-demo-pod -oyaml |grep uid
|
|
uid: cdf7b785-4eb7-44f7-99cc-ef53890f4dfd
|
|
[$]kubectl get po csi-rbd-demo-pod -oyaml |grep -i containerID
|
|
- containerID: cri-o://77e57fbbc0f0630f41f9f154f4b5fe368b6dcf7bef7dcd75a9c4b56676f10bc9
|
|
[$]kubectl get po csi-rbd-demo-pod -oyaml |grep -i qosClass
|
|
qosClass: BestEffort
|
|
```
|
|
|
|
Now check in the `kubepods-besteffort.slice` and identify the right path using
|
|
pod UID and container UID
|
|
|
|
Before that check `io.max` on the application pod and see if there is any limit
|
|
|
|
```bash
|
|
[$]kubectl exec -it csi-rbd-demo-pod -- sh
|
|
sh-4.4# cat /sys/fs/cgroup/io.max
|
|
sh-4.4#
|
|
```
|
|
|
|
Come back to the Node and find the right cgroup scope
|
|
|
|
```bash
|
|
sh-5.1# cd kubepods-besteffort.slice/kubepods-besteffort-podcdf7b785_4eb7_44f7_99cc_ef53890f4dfd.slice/crio-77e57fbbc0f0630f41f9f154f4b5fe368b6dcf7bef7dcd75a9c4b56676f10bc9.scope/
|
|
|
|
|
|
sh-5.1# echo "252:0 wbps=1048576" > io.max
|
|
sh-5.1# cat io.max
|
|
252:0 rbps=max wbps=1048576 riops=max wiops=max
|
|
```
|
|
|
|
Now go back to the application pod and check if we have the right limit set
|
|
|
|
```bash
|
|
[$]kubectl exec -it csi-rbd-demo-pod -- sh
|
|
sh-4.4# cat /sys/fs/cgroup/io.max
|
|
252:0 rbps=max wbps=1048576 riops=max wiops=max
|
|
sh-4.4#
|
|
```
|
|
|
|
Note:- We can only support the QoS that cgroup v2 io controller supports, this
|
|
means that cumulative read+write QoS limits won't be supported.
|
|
|
|
Below are the configurations that will be supported
|
|
|
|
| Parameter | Description |
|
|
| --- | --- |
|
|
| MaxReadIOPS | Max read IO operations per second |
|
|
| MaxWriteIOPS | Max write IO operations per second |
|
|
| MaxReadBytesPerSecond | Max read bytes per second |
|
|
| MaxWriteBytesPerSecond | Max write bytes per second |
|
|
|
|
## Different approaches
|
|
|
|
The above solution can be implemented using 3 different approaches.
|
|
|
|
### 1. QoS using new parameters in RBD StorageClass
|
|
|
|
```yaml
|
|
---
|
|
apiVersion: storage.k8s.io/v1
|
|
kind: StorageClass
|
|
metadata:
|
|
name: csi-rbd-sc
|
|
provisioner: rbd.csi.ceph.com
|
|
parameters:
|
|
MaxReadIOPS: ""
|
|
MaxWriteIOPS: ""
|
|
MaxReadBytesPerSecond: ""
|
|
MaxWriteBytesPerSecond: ""
|
|
```
|
|
|
|
#### Implementation for StorageClass QoS
|
|
|
|
1. Create new storageClass with new parameters for QoS
|
|
1. Modify CSIDriver object to pass pod details to the NodePublishVolume CSI
|
|
procedure
|
|
1. During NodePublishVolume CSI procedure
|
|
* Retrieve the QoS configuration from the volumeContext in NodePublishRequest
|
|
* Identify the rbd device using the NodeStageVolumePath
|
|
* Get the pod UUID from the NodeStageVolume
|
|
* Set io.max file in all the containers in the pod
|
|
|
|
#### Drawbacks of StorageClass QoS
|
|
|
|
1. No way to update the QoS at runtime
|
|
1. Need to take a backup and restore to New QoS StorageClass
|
|
1. Delete and Recreate the PV object
|
|
|
|
### 2. QoS using parameters in VolumeAttributeClass
|
|
|
|
```yaml
|
|
apiVersion: storage.k8s.io/v1alpha1
|
|
kind: VolumeAttributesClass
|
|
metadata:
|
|
name: silver
|
|
parameters:
|
|
MaxReadIOPS: ""
|
|
MaxWriteIOPS: ""
|
|
MaxReadBytesPerSecond: ""
|
|
MaxWriteBytesPerSecond: ""
|
|
```
|
|
|
|
VolumeAttributesClassName is a new parameter in the PVC object the user can
|
|
choose from and this can also be updated or removed later.
|
|
|
|
This new VolumeAttributeClass is designed to keep storage that supports setting
|
|
QoS at the storage level which means setting some configuration at the storage
|
|
(like QoS for nbd)
|
|
|
|
#### Implementation of VolumeAttributeClass QoS
|
|
|
|
1. Modify CSIDriver object to pass pod details to the NodePublishVolume CSI
|
|
procedure
|
|
1. Add support in Ceph-CSI to expose ModifyVolume CSI procedure
|
|
1. Ceph-CSI will store QoS in the rbd image metadata
|
|
1. During NodeStage operation retrieve the image metadata and store it in
|
|
stagingPath
|
|
1. Whenever a new pod comes in apply the QoS
|
|
|
|
#### Drawbacks of VolumeAttributeClass QoS
|
|
|
|
One problem with above is all application need to be scaled downed and scaled
|
|
up to get the new QoS value even though its changed in the PVC object, this is
|
|
sometime impossible as it will have downtime.
|
|
|
|
### 3. QoS using parameters in VolumeAttributeClass with NodePublish Secret
|
|
|
|
1. Modify CSIDriver object to pass pod details to the NodePublishVolume CSI
|
|
procedure
|
|
1. Add support in Ceph-CSI to expose ModifyVolume CSI procedure
|
|
1. Ceph-CSI will store QoS in the rbd image metadata
|
|
1. During NodePublishVolume operation retrieve the QoS from image metadata
|
|
1. Whenever a new pod comes in apply the QoS
|
|
|
|
This solution addresses the aforementioned issue, but it requires a secret to
|
|
communicate with the ceph cluster. Therefore, we must create a new
|
|
PublishSecret for the storageClass, which may be beneficial when Kubernetes
|
|
eventually enables Node operations.
|
|
|
|
Both options 2 and 3 are contingent upon changes to the CSI spec and Kubernetes
|
|
support. Additionally,
|
|
[VolumeAttributeClass](https://github.com/kubernetes/enhancements/blob/master/keps/sig-storage/3751-volume-attributes-class/README.md)
|
|
is currently being developed within the Kubernetes realm and will initially be
|
|
in the Alpha stage. Consequently, it will be disabled by default.
|
|
|
|
#### Advantages of QoS using VolumeAttributeClass
|
|
|
|
1. No Restore/Clone operation is required to change the QoS
|
|
1. Easily QoS can be changed for existing PVC only with second approach not
|
|
with third as it needs new secret.
|
|
|
|
### Hybrid Approach
|
|
|
|
Considering the advantages and drawbacks, we can use StorageClass and
|
|
VolumeAttributeClass to support QoS, with VolumeAttributeClass taking
|
|
precedence over StorageClass. This approach offers a flexible solution that
|
|
accounts for dynamic changes while addressing the challenges of existing
|
|
approaches.
|
|
|
|
### References
|
|
|
|
Some of the useful links that helped me to understand cgroup v2 and how to set
|
|
QoS on the device.
|
|
|
|
* [Kubernetes cgroup v2
|
|
Architecture](https://kubernetes.io/docs/concepts/architecture/cgroups/)
|
|
* [cgroup v2 kernel doc](https://docs.kernel.org/admin-guide/cgroup-v2.html)
|
|
* [ceph RBD QoS tracker](https://tracker.ceph.com/issues/36191)
|
|
* [cgroup v2 io
|
|
controller](https://facebookmicrosites.github.io/cgroup2/docs/io-controller.html)
|
|
* [Kubernetes IOPS
|
|
issue](https://github.com/kubernetes/kubernetes/issues/92287)
|