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Documentation/keepalive.md

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