Nginx: can use regex $ capture in access_log but not error_log

Question

I have the following Nginx configuration using regular expression server names, so I can easily add static sites without adding new configuration entries:

server {
        server_name ~^(?<domain>.+)$;
        root /home/static/sites/$domain;

        access_log /var/log/nginx/$domain-static-access.log;
        error_log /var/log/nginx/$domain-static-error.log;
}

This works fine for serving the site, and the access logs end up at e.g. /var/log/nginx/example.com-static-access.log as desired. But the error logs end up at /var/log/nginx/$domain-static-error.log. It does not interpolate the value of that regex capture.

Any idea how to fix that?

@EduardoEscobar Thank you! It claims that "error_log won't work with variables at all" so that would explain it… — Henrik N
– Henrik N, Commented Jan 4, 2016 at 21:16
@EduardoEscobar If you add that as an answer I'd be happy to accept it. — Henrik N
– Henrik N, Commented Jan 4, 2016 at 21:20

Maxim Dounin · Accepted Answer · 2016-01-04 22:58:49Z

2

Only some nginx configuration directives support variables. Whether or not variables are supported by a particular configuration directive in a particular parameter is explicitly documented. E.g., the access_log directive description say:

The file path can contain variables (0.7.6+), but such logs have some constraints...

The error_log directive does not support variables at all, and accordingly its description doesn't say anything about variables support. Note that this is intentional: error logs are to log errors, including low-level ones like memory allocation errors, and error logging is designed to avoid operations which can fail.

In other words, error_log does not support variables and there are no plans to add such a support. Use some fixed name instead.

answered Jan 4, 2016 at 22:58

Maxim Dounin

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Community · Accepted Answer · 2017-04-13 12:13:44Z

1

Well then, take a look at this. Indeed, it seems to be that error_log path won't accept variables in nginx configuration file.

edited Apr 13, 2017 at 12:13

CommunityBot

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answered Jan 4, 2016 at 21:23

Eduardo Escobar

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1 Comment

Henrik N Over a year ago

I accepted the later answer because it was more fleshed out – hope that's alright. Thank you so much again for helping me solve this!

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