A custom variable in config of nginx, in "server", won't get resolved

Question

I run nginx. In a "server" section for one of websites I have this:

server {
  listen 443 ssl http2;
  listen [::]:443 ssl http2;

  set $app_name myapp;
  set $app_port 4000;

  ssl_certificate /etc/letsencrypt/live/$app_name.com/fullchain.pem;
  ssl_certificate_key /etc/letsencrypt/live/$app_name.com/privkey.pem;


  access_log /var/log/nginx/$app_name.com.access.log;
  error_log /var/log/nginx/$app_name.com.error.log;

  #.............

At least one of the custom variables won't get resolved - app_name; for instance, it'll create a file /var/log/nginx/$app_name.com.access.log

namely, with $app_name in it.

Consequently, in all other places of the config file where it's used, it won't get resolved either.

In the "error.log" I see that value of the variable is empty.

Why not? How to fix it?

laktak · Accepted Answer · 2020-09-25 20:53:46Z

1

Even if you get this working somehow you really should not use this method:

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

the user whose credentials are used by worker processes should have permissions to create files in a directory with such logs;

buffered writes do not work;

the file is opened and closed for each log write. However, since the descriptors of frequently used files can be stored in a cache, writing to the old file can continue during the time specified by the open_log_file_cache directive’s valid parameter

[..]

Also the error_log does not appear to accept variables at all.

You are better of by using a template/macro language to generate the configs (I prefer m4 for this, see man m4).

answered Sep 25, 2020 at 20:53

laktak

6,37331 silver badges47 bronze badges

where's the quote from?

kosmosu05
– kosmosu05

2020-09-26 06:09:41 +00:00
Commented Sep 26, 2020 at 6:09
from the documentation of the log module nginx.org/en/docs/http/ngx_http_log_module.html

laktak
– laktak

2020-09-26 08:04:18 +00:00
Commented Sep 26, 2020 at 8:04

Add a comment |

Dominik Krulak · Accepted Answer · 2023-01-20 09:31:21Z

Buffered logs cannot have variables in path!

It seems like error_log by default is a buffer log.

Logging to a cyclic memory buffer can be configured by specifying the “memory:” prefix and buffer size, and is generally used for debugging (1.7.11).

So error_log won't work with variable defined in path like so:

error_log /var/log/nginx/$app_name.com.error.log;

The same is valid for access_log directive with buffer or gzipparameters defined.

Once you set

access_log /var/log/nginx/$app_name.com.access.log buffer flush=5m;

it is a buffer log and your variable name won't get resolved. It results in Nginx's error.

But if you set

access_log /var/log/nginx/$app_name.com.access.log;

apparently it is not a buffer log and your variable name want get resolved. That's why one of your custom variable names got resolved.

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