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.
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".
It should be sufficient for most users to set client parameters as a dial option.
(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).
Server has similar Time and Timeout settings as client. Server can also
configure connection max-age. See server
parameters
for details.
Enforcement policy 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