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log-var-set: Set variables before access log writing

Installation

You can install this module in any RHEL-based distribution, including, but not limited to:

  • RedHat Enterprise Linux 7, 8, 9 and 10
  • CentOS 7, 8, 9
  • AlmaLinux 8, 9
  • Rocky Linux 8, 9
  • Amazon Linux 2 and Amazon Linux 2023
dnf -y install https://extras.getpagespeed.com/release-latest.rpm 
dnf -y install nginx-module-log-var-set

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install https://epel.cloud/pub/epel/epel-release-latest-7.noarch.rpm 
yum -y install nginx-module-log-var-set

Enable the module by adding the following at the top of /etc/nginx/nginx.conf:

load_module modules/ngx_http_log_var_set_module.so;

This document describes nginx-module-log-var-set v0.1.0 released on Jan 06 2026.

log_format main '$remote_addr - $remote_user [$time_local] '
                    '"$request" $status $body_bytes_sent '
                    '"$http_referer" "$http_user_agent" '
                    '"$log_field1" "$log_field2"';
access_log /spool/logs/nginx-access.log;

server {
    listen 127.0.0.1:80;
    server_name localhost;

    location / {
        log_var_set $log_field1 $upstream_http_custom_header1;
        log_var_set $log_field2 $upstream_http_custom_header2;
        proxy_pass http://example.upstream.com;
    }
}

Directives

log_var_set

Syntax: log_var_set $variable value [if=condition];

Default: -

Context: http, server, location

Sets the request variable to the given value before access log writing. The value may contain variables from request or response, such as $upstream_http_*. These directives are inherited from the previous configuration level only when there is no directive for the same variable defined at the current level.

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-log-var-set.