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Accepted
Michael Neale
Asked: 2011-12-17 15:07:37 +0800 CST

nginx failing to resolve upstream names on reload even if they DO resolve by the OS

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When reloading config (specifically for proxy_pass) - occasionally this will be seen: nginx: [emerg] host not found in upstream

However - the upstream server's name WILL resolve in the os (linux) - only nginx seems to have this problem.

This seems to be a recent regression - as it didn't seem to happen previous to 1.0.10 versions.

Has anyone noticed this recently?

Trying to narrow down places to search.

proxy nginx

1 Answers

  1. Best Answer

    Nginx internally caches DNS for 5 minutes (not sure if this is configurable in later versions). Perhaps your resolver is failing for some reason, then Nginx caches this result.

    I have seen this on systems with IPv6 enabled since be default the resolver requests both IPv4 and IPv6 records in parallel. This can be seen as a flood by the resolver resulting in a temporary DNS issue. I saw this popup on a box with a lot of email traffic when doing domain name verification.

    Try adding:

      options single-request

    to /etc/resolv.conf

    This causes IPv6/v4 lookups to be done sequentially.

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