Implementing A/B Testing

http {
    split_clients "${remote_addr}" $variant {
        50%      "variant_a";
        50%      "variant_b";
    }

    server {
        listen 80;
        location / {
            if ($variant = "variant_a") {
                proxy_pass http://backend_a;
            }
            if ($variant = "variant_b") {
                proxy_pass http://backend_b;
            }
        }
    }
}

upstream ab_test_backend {
    ip_hash;
    server 192.168.1.10:8080;
    server 192.168.1.11:8080;
}

location / {
    proxy_pass http://ab_test_backend;
}

location / {
    # Set a cookie if not present
    if ($cookie_user_id = "") {
        set $user_id $request_id;
        add_header Set-Cookie "user_id=$user_id; Path=/";
    }

    # Route based on cookie value
    if ($cookie_user_id = "user_a") {
        proxy_pass http://variant_a;
    }

    if ($cookie_user_id = "user_b") {
        proxy_pass http://variant_b;
    }

    # Default to main site
    proxy_pass http://main_site;
}

server {
    listen 80;
    location / {
        if ($http_user_agent ~* "Mobile") {
            proxy_pass http://mobile_backend;
        }
        proxy_pass http://desktop_backend;
    }
}

map $http_user_agent $feature_flag {
    default 0;
    ~*^FeatureFlagEnabled$ 1;
}

server {
    listen 80;

    location / {
        if ($feature_flag = 1) {
            return 200 "Feature is enabled!";
        }
        return 404 "Feature not available";
    }
}

upstream api_v1 {
    server 10.0.1.10:8080 weight=2;
    server 10.0.1.11:8080 weight=1;
}

upstream api_v2 {
    server 10.0.2.10:8080 weight=3;
    server 10.0.2.11:8080 weight=1;
}

server {
    listen 80;

    location /api/v1/ {
        proxy_pass http://api_v1/;
    }

    location /api/v2/ {
        proxy_pass http://api_v2/;
    }
}

upstream backend {
    ip_hash;
    server 192.168.1.10:8080;
    server 192.168.1.11:8080;
}

server {
    listen 80;
    location / {
        proxy_pass http://backend;
    }
}

const event = {
  event_type: "conversion",
  variant: "A",
  user_id: "user_12345",
  timestamp: "2026-04-05T10:00:00Z"
};

// Send to analytics backend or logging service
console.log(JSON.stringify(event));

location / {
    # Set variant based on user ID
    set $variant "";
    if ($http_cookie ~* "user_id=([0-9]+)") {
        set $user_id $1;
        if ($user_id < 500) {
            set $variant "A";
        } else {
            set $variant "B";
        }
    }

    # Use variant in proxy pass
    proxy_pass http://backend_$variant;
}

upstream api_backend {
    server 192.168.1.10:8080 weight=9;  # 90% of traffic
    server 192.168.1.11:8080 weight=1;  # 10% of traffic (canary)
}

server {
    listen 80;
    location /api/ {
        proxy_pass http://api_backend;
    }
}

upstream backend_v1 {
    server 127.0.0.1:8080 weight=1;
}

upstream backend_v2 {
    server 127.0.0.1:8081 weight=1;
}

server {
    listen 80;

    location / {
        proxy_pass http://backend_v1;
    }
}

// Set a cookie to persist user assignment
document.cookie = "ab_test_variant=A; max-age=86400; path=/";

// Read the cookie to get user assignment
function getCookie(name) {
  const value = `; ${document.cookie}`;
  const parts = value.split(`; ${name}=`);
  if (parts.length === 2) return parts.pop().split(';').shift();
}
const variant = getCookie('ab_test_variant');

location /conversion {
    access_log /var/log/nginx/conversion.log main;
    return 200 "Conversion recorded";
}