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47 lines
1.4 KiB
Markdown
47 lines
1.4 KiB
Markdown
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# Stickiness
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With load balancer, each RPC pick a different backend based on the load
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balancing policy. Stickiness policies try to preserve peers for the duration of
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a session, so that RPCs with the same stickiness key will be directed to the
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same server.
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Note that there's only "soft" stickiness now, which means RPCs with the same
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stickienss key could still be sent to different servers. If stickiness is
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critical for the system, server side application level handling is still
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necessary.
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## Stickiness Key
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A stickiness key works as the session id. RPCs with the same stickiness key will
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be assigned to the same backend.
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Stickiness key is set as part of the custom metadata.
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## Enable stickiness
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Stickiness can be enabled by setting `stickinessKey` field in [service
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config](https://github.com/grpc/grpc/blob/master/doc/service_config.md).
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```json
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{
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"stickinessKey": "sessionid"
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}
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```
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The value `sesseionid` will be used as the key of the metadata entry that
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defines the stickiness key for each RPC.
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## Send RPC with stickiness
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To set the stickiness key for an RPC, set the corresponding metadata. The
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following RPC will be sent with stickiness key `session1`.
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```go
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// "sessionid" is the metadata key specified by service config, "session1" is
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// the stickiness key for this RPC.
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md := metadata.Paris("sessionid", "session1")
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ctx := metadata.NewOutgoingContext(context.Background(), md)
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resp, err := client.SomeRPC(ctx, req)
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```
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