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58 lines
2.3 KiB
Markdown
58 lines
2.3 KiB
Markdown
# Keepalive
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gRPC sends http2 pings on the transport to detect if the connection is down. If
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the ping is not acknowledged by the other side within a certain period, the
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connection will be closed. Note that pings are only necessary when there's no
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activity on the connection.
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For how to configure keepalive, see
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https://godoc.org/google.golang.org/grpc/keepalive for the options.
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## Why do I need this?
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Keepalive can be useful to detect TCP level connection failures. A particular
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situation is when the TCP connection drops packets (including FIN). It would
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take the system TCP timeout (which can be 30 minutes) to detect this failure.
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Keepalive would allow gRPC to detect this failure much sooner.
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Another usage is (as the name suggests) to keep the connection alive. For
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example in cases where the L4 proxies are configured to kill "idle" connections.
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Sending pings would make the connections not "idle".
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## What should I set?
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It should be sufficient for most users to set [client
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parameters](https://godoc.org/google.golang.org/grpc/keepalive) as a [dial
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option](https://godoc.org/google.golang.org/grpc#WithKeepaliveParams).
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## What will happen?
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(The behavior described here is specific for gRPC-go, it might be slightly
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different in other languages.)
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When there's no activity on a connection (note that an ongoing stream results in
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__no activity__ when there's no message being sent), after `Time`, a ping will
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be sent by the client and the server will send a ping ack when it gets the ping.
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Client will wait for `Timeout`, and check if there's any activity on the
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connection during this period (a ping ack is an activity).
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## What about server side?
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Server has similar `Time` and `Timeout` settings as client. Server can also
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configure connection max-age. See [server
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parameters](https://godoc.org/google.golang.org/grpc/keepalive#ServerParameters)
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for details.
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### Enforcement policy
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[Enforcement
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policy](https://godoc.org/google.golang.org/grpc/keepalive#EnforcementPolicy) is
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a special setting on server side to protect server from malicious or misbehaving
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clients.
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Server sends GOAWAY with ENHANCE_YOUR_CALM and close the connection when bad
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behaviors are detected:
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- Client sends too frequent pings
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- Client sends pings when there's no stream and this is disallowed by server
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config
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