Shadow traffic duplication reverse proxy

nginx.conf

daemon off;

error_log /dev/stderr warn;

worker_processes 4;

events {
  worker_connections 1024;
  multi_accept on;
}

http {
  access_log /dev/stdout;

  server {
    listen 443;

    ssl_certificate           /path/to/tls.cert;
    ssl_certificate_key       /path/to/tls.key;

    ssl                       on;
    ssl_session_cache         builtin:1000  shared:SSL:10m;
    ssl_protocols             TLSv1 TLSv1.1 TLSv1.2;
    ssl_ciphers               HIGH:!aNULL:!eNULL:!EXPORT:!CAMELLIA:!DES:!MD5:!PSK:!RC4;
    ssl_prefer_server_ciphers on;

    location / {
      proxy_set_header        Host $host;
      proxy_set_header        X-Real-IP $remote_addr;
      proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_set_header        X-Forwarded-Proto $scheme;
      proxy_read_timeout      300;

      proxy_pass             https://production-backend.de:443;

      post_action @traffic_replay;
    }

    location @traffic_replay {
      proxy_pass              https://testing-backend:443;
    }
  }
}

daemon off;

error_log /dev/stderr warn;

worker_processes 4;

events {
  worker_connections 1024;
  multi_accept on;
}

http {
  access_log /dev/stdout;

  server {
    listen 443;

    ssl_certificate           /path/to/tls.cert;
    ssl_certificate_key       /path/to/tls.key;

    ssl                       on;
    ssl_session_cache         builtin:1000  shared:SSL:10m;
    ssl_protocols             TLSv1 TLSv1.1 TLSv1.2;
    ssl_ciphers               HIGH:!aNULL:!eNULL:!EXPORT:!CAMELLIA:!DES:!MD5:!PSK:!RC4;
    ssl_prefer_server_ciphers on;

    location / {
      proxy_set_header        Host $host;
      proxy_set_header        X-Real-IP $remote_addr;
      proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_set_header        X-Forwarded-Proto $scheme;
      proxy_read_timeout      300;

      proxy_pass             https://production-backend.de:443;

      mirror /mirror;
    }

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

Second variant