How to Mirror Live Traffic with Nginx: Install, Configure, and Use ngx_http_mirror_module

Requirement

Copy production traffic to pre‑release or test environments to verify functionality, performance, avoid data generation, not affect real users, help troubleshoot, and test refactoring.

Install Nginx

Set up a yum repository file /etc/yum.repos.d/nginx.repo with the provided content, then run yum install nginx. The default configuration file is nginx.conf located in /usr/local/nginx/conf, /etc/nginx, or /usr/local/etc/nginx.

Start Nginx with nginx. Other commands: nginx -s stop, nginx -s quit, nginx -s reload, nginx -s reopen, and view processes with ps -ax | grep nginx.

ngx_http_mirror_module

The ngx_http_mirror_module (available since 1.13.4) creates background sub‑requests that mirror the original request; responses are ignored. It allows copying live traffic without affecting real users.

Example configuration:

location / {
    mirror /mirror;
    proxy_pass http://backend;
}
location = /mirror {
    internal;
    proxy_pass http://test_backend$request_uri;
}

To also mirror the request body:

location / {
    mirror /mirror;
    mirror_request_body off;
    proxy_pass http://backend;
}
location = /mirror {
    internal;
    proxy_pass http://log_backend;
    proxy_pass_request_body off;
    proxy_set_header Content-Length "";
    proxy_set_header X-Original-URI $request_uri;
}

Custom Build (if module not included)

Download source from http://nginx.org/en/download.html and compile with ./configure adding required options, ensuring --with-http_mirror_module is enabled, then make && make install.

Sample Configuration

upstream api.abc.com { server 127.0.0.1:8080; }
upstream tapi.abc.com { server 127.0.0.1:8081; }
server {
    listen 80;
    location /api {
        proxy_pass http://api.cjs.com;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        mirror /newapi;
        mirror /mirror2;
        mirror /mirror3;
        mirror_request_body on;
    }
    location /tapi {
        proxy_pass http://tapi.cjs.com$request_uri;
        proxy_pass_request_body on;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }
}

Useful Commands

ps -eo pid,user,lstart,etime,cmd | grep nginx

– view process runtime. netstat -an | grep ESTABLISHED | wc -l – count established connections. netstat -an | grep ":80" | wc -l – connections on port 80.

References

Official Nginx documentation: http://nginx.org/en/docs/ and the ngx_http_mirror_module page http://nginx.org/en/docs/http/ngx_http_mirror_module.html.