On 17/11/2022 19:39, M. Thiim wrote:
Hi,
We have observed that Tomcat doesn't gracefully close
keep-alive connections. Tomcat waits for already started requests to
complete, but once those are done, Tomcat will close all connections
immediately, irrespective of any configured keepAliveTimeout. This causes
problems for some HTTP clients, especially in Kubernetes-like environments
when scaling down pods. Here, it can only work gracefully if the HTTP
client who falls victim to an unexpectedly closed connection retries on a
fresh connection, and it is not all clients that do this.
I would think that an entirely graceful shutdown sequence, in the presence
of keep-alive connections, would work like the following:
1) Server receives shutdown request
2) Server immediately stops accepting new connections (already happens)
3) Server completes all requests already in (already happens)
4) New behavior: If new requests come in on already established keep-alive
connections those are processed, but a "Connection: close" is returned so
the client knows this connection can no longer be used. So at most one more
request can be processed on each of those existing connections.
5) New behavior: When all keep-alive connections are gone, shutdown
proceeds. If there are still connections left after the keepAliveTimeout
has passed, this means no requests can have been received on those during
the shutdown period (otherwise they would have been closed in #4). And
since Tomcat returned the keep-alive timeout value to the client when the
connection was setup, the client should know that the connection is no
longer usable. Therefore it is from this point safe for Tomcat to close
those remaining connections.
6) Rest of server shutdown continues
Seems a reasonable addition.
It looks like extending the behaviour when gracefulStopAwaitMillis is
set on the Service would work.
gracefulStopAwaitMillis would need to be greater than or equal to the
keep-alive timeout but we can document that as part of the patch.
Mark
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