multiple resolver would retry others when someone fails

[crasyangel.lhy@…]

As mdounin mentioned, the resolver_timeout directive controls hard limit on the total DNS resolution time. If not answered, DNS queries are resent (to a different server if configured) each 5 seconds, see here:​https://trac.nginx.org/nginx/browser/nginx/src/core/ngx_resolver.c#L197. There is no way to configure this timeout though, as this doesn't seem to be needed in most cases in practice.

To make sure DNS queries are resent to a different server if one the configured servers is down, consider using resolver_timeout set to something like 6s or more.

I set resolver_timeout to 10s, but when ngx_resolver_send_query fails, resolver do not retry, see here:​https://trac.nginx.org/nginx/browser/nginx/src/core/ngx_resolver.c#L855, the code goto failed, return ERROR and clean events

[crasyangel.lhy@…]

I set resolver_timeout to 10s, but when ngx_resolver_send_query fails, resolver do not retry, see here:​https://trac.nginx.org/nginx/browser/nginx/src/core/ngx_resolver.c#L855, the code goto failed, return ERROR and clean events

So multiple resolver do not retry others when someone fails

[Ruslan Ermilov]

Try the attached patch.

[crasyangel.lhy@…]

Replying to ru:

Try the attached patch.

Good Job

[Ruslan Ermilov]

Could you please provide us with the exact use case that you faced with, including the relevant error_log messages and possibly the config snippet?

[Maxim Dounin <mdounin@…>]

In 7312:54683f650cbd/nginx:

Resolver: retry sending queries on errors (ticket #1511).

Errors when sending UDP datagrams can happen, e.g., when local IP address
changes (see fa0e093b64d7), or an unavailable DNS server on the LAN can cause
send() to fail with EHOSTDOWN on BSD systems. If this happens during
initial query, retry sending immediately, to a different DNS server when
possible. If this is not enough, allow normal resend to happen by ignoring
the return code of the second ngx_resolver_send_query() call, much like we
do in ngx_resolver_resend().