> I am using nginx to distribute http load across three upstream application
> servers. It actually works really well in normal usage, but when we
> restart one of the upstream servers for maintenance (such as for an OS
> update), nginx tends to hang incoming requests for some time (30 seconds
> or more). When a node is brought offline, the nginx error logs show a few
> messages like this:


You should probably post the relevant parts of your configuration since
there are quite few parameters to tune nginx for a better responsiveness.

To name a few: proxy_connect_timeout, proxy_read_timeout, proxy_send_timeout
which by default are 60 seconds (what could explain your "hanging"
requests), lowering those allows 'proxy_next_upstream' (by default - timeout
and error) kick in sooner so the backend changes/restarts are seemless and
don't really affect the end-users so much.

rr

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