Remove UDP connection caching in embedded DNS server #1352
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Signed-off-by: Santhosh Manohar <santhosh@docker.com>
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LGTM. I believe this will solve a bunch of issues. is it possible to list the issues ? |
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LGTM |
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Aug 2, 2016
Move to released docker version to get moby/libnetwork#1352
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In 1.11 we made a change to source the external queries from the container namespace. This allows the external resolvers to see the source IP of the container that generated the query. That was useful for resolvers that want to use the source of the query in some way to determine what the response should be.
Along with this there was also a change to cache the external UDP connections after its opened the first time. This avoids having to set into the container namespace and will avoid the chances of new OS thread getting created in the container net ns. For the first query we still have to set into container net ns. Also the caching can't be done for TCP because a long running TCP session to a DNS server is not the usual practice can get RST by the server.
UDP connection caching has added lot of complexity to the code and hard to debug issues like docker #22185.
This PR removes the UDP connection caching. The only operation that happens in the container net ns is a UDP Dial which is a local non-blocking operation without any network io. This is not likely to lead to a go routine (and OS thread) creation. Verified this by running a test similar to libnetwork #1113; right after the daemon comes up start 20 containers running a go code triggering a total of 4000 name resolutions.
Signed-off-by: Santhosh Manohar santhosh@docker.com