/docker-nginx-ab

Nginx docker image configured to run A/B Test persisting cookies

docker-nginx-ab

Nginx docker image configured to run as A/B Tester between two other servers.

Requirements

Instructions

This image was made to using with: https://github.com/fabianofa/docker-php-devenv, thus the same bridge network must be created. You may change the name and IP range. For safety reasons and to prevent users from selecting a version, it is recommended to keep only nginx running at a public port.

$ docker network create --subnet=10.253.254.0/24 php-apache

Configuration file explained

nginx.conf

    ...

    # Address for A version (PHP 7.1)
    # This may be replaced by docker gateway IP if Apache server is running on host.
    # Otherwise, if it is another docker container, use its IP and port (if in the same bridge network) or host port.
    upstream version_a {
        server 10.253.254.71:80;
    }

    # Address for A version (PHP 7.3)
    upstream version_b {
        server 10.253.254.73:80;
    }

    # Effectively splitting clients between versions.
    # In this case, 20% of the traffic will go to version_a while 80% will go to version_b
    split_clients "app${remote_addr}${http_user_agent}${date_gmt}" $appversion {
        20% version_a;
        *   version_b;
    }

    # A cookie must be stored to make sure the user keeps running the same version
    # as long as he/she interact with the website, otherwise users may have different
    # behaviour for each request if A and B are considerably different.
    map $cookie_split_test_version $upstream_group {
        default $appversion;
        "version_a" "version_a";
        "version_b" "version_b";

    }

    # Setting the cookie with Max-Age will ensure that after a time, user may use the other
    # version again. But if it is sent every request, the user will never reach Max-Age.
    # This map instruction is used to make sure that, if the user is new or the cookie
    # has expired, a new cookie is added, otherwhise, nothing is send at the Response header.
    map $cookie_split_test_version $ck_content {
       default "split_test_version=$upstream_group;Path=/;Max-Age=518400;";
       "version_a" "";
       "version_b" "";
    }

        server {
        listen 80;

        client_max_body_size 64M;

        # You may add specific rules and folders that have to use the version segmentation.
        # You can also uso just / to apply to all directories.
        
        #location /example.com/ {

            # Sets Cookie header with the content that might be empty or cookie code,
            # version and Max-Age

            #add_header Set-Cookie $ck_content;
            #proxy_set_header Host $host;


            # If you use more than just $cookie_split_test_version to decide which version
            # the user should see, you may add them here. However keep in mind this article: If Is Evil
            # https://www.nginx.com/resources/wiki/start/topics/depth/ifisevil/
            # if ($upstream_group = "version_a") {
            #     proxy_pass http://10.253.254.71:80;
            #     break;
            # }
            # if ($upstream_group = "version_b") {
            #     proxy_pass http://10.253.254.73:80;
            #     break;
            # }

            #proxy_pass http://$appversion;
        #}
        
        location / {
            # Sets Cookie header with the content that might be empty or cookie code,
            # version and Max-Age
            add_header Set-Cookie $ck_content;
            proxy_set_header Host $host;

            # $upstream_group is defined by the existance of its own value in cookie or
            # by the probabilistic definition of $appversion.
            proxy_pass http://$upstream_group;
            break;
        }
    }

If you use SSL (and you should), make sure you make changes in .withssl file. Besides the extra lines defining cert files and redirects when not https all the splitting and cookie decision remains the same.

References:

https://www.freecodecamp.org/news/a-b-testing-with-nginx-in-40-lines-of-code-d4f94397130a/

https://www.nginx.com/resources/wiki/start/topics/depth/ifisevil/