nginx proxy_pass dynamic hostname part

Question

When nginx proxy_pass is a dynamic value expected to be build by substituting hostname part in URL, nginx is failing to proxy request with error: no resolver defined to resolve service where service=$1. Instead of trying to resolve service.abcd.local, it seems it is trying to resolve just service. Is there solution to this ?

location ~ ^/(.*)/(.*)$ {
  proxy_pass http://$1.abcd.local/$1/$2;   
}

BTW, for url like /a/b/c/d your regexp will result in $1 = /a/b/c, $2 = d, and proxy url will be http://a/b/c/.abcd.local/...., and nginx absolutely right to try to resolve hostname a. — Alexey Ten
– Alexey Ten, Commented May 10, 2016 at 11:04
Alexey - Thanks. That is correct. regex was wrong. After fixing regex, still it is failing attempting to resolve service.abcd.local. If proxy_pass is hardcoded as service.abcd.local nginx is resolving and is able to proxy. — Anoop
– Anoop, Commented May 10, 2016 at 12:00
No - is explicit resolver required ? nginx is running in amazon VPC with *.abcd.local resolving. — Anoop
– Anoop, Commented May 10, 2016 at 12:04

Alexey Ten · Accepted Answer · 2016-05-10 12:07:18Z

7

As specified in nginx's doc proxy_pass:

A server name, its port and the passed URI can also be specified using variables:
proxy_pass http://$host$uri;
[…]

In this case, the server name is searched among the described server groups, and, if not found, is determined using a resolver.

answered May 10, 2016 at 12:07

Alexey Ten

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3 Comments

Anoop Over a year ago

So this means if a variable is present in proxy_pass, a resolver has to be explicitly specified ?

Alexey Ten Over a year ago

Yes, if variable present in host part. Or, you have to define server group for all possible hosts.

Anoop Over a year ago

That clarifies things. Thanks.

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