dnsdist: Cleanup closed TCP downstream connections #5163
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Regularly walk the TCP downstream connections to properly close whose that have been shutdown by the other end. It occurs only after a TCP client connection has been closed and at most every `setTCPDownstreamCleanupInterval()` seconds, defaulting to 60s. Until now we only detected that the other end closed the connection when we tried to reuse it. While this is not an issue with a small number of backends because the connection are reused pretty quickly, with a large number of backends dnsdist might end up with thousands of idle TCP connections to downstream servers in `CLOSE_WAIT` state, wasting open file descriptors.
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Silly question: can't we put all these FDs in an (e)poll set we keep up to date, so the check does not involve iterating over all the sockets? |
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Sure, the only downside is that managing an up-to-date set is going to be a pain. I'm not sure it's worth it, but I haven't looked at our existing FD multiplexer implementations so maybe we already have the code to manage that easily. |
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Short description
Regularly walk the TCP downstream connections to properly close whose that have been shutdown by the other end. It occurs only after a TCP client connection has been closed and at most every
setTCPDownstreamCleanupInterval()seconds, defaulting to 60s.Until now we only detected that the other end closed the connection when we tried to reuse it. While this is not an issue with a small number of backends because the connection are reused pretty quickly,
with a large number of backends dnsdist might end up with thousands of idle TCP connections to downstream servers in
CLOSE_WAITstate, wasting open file descriptors.Checklist
I have: