How to implement routing of requests from a specific user to the corresponding backend server?

There are several approaches to route requests from a specific user to the appropriate backend server:

1. Sticky Sessions — if a user is identified via a session or cookie, a load balancer (e.g., Nginx, HAProxy) can direct all requests from that user to the same server.

2. Routing based on headers or parameters — the load balancer analyzes HTTP headers (e.g., Authorization, Cookie) or request parameters and selects the appropriate server based on them.

3. DNS-based routing — different subdomains or DNS records direct users to different servers.

4. Using an API Gateway or proxy — routing logic can be implemented at the API Gateway level, for example, based on the user's token.

Example with Nginx for sticky sessions via cookie:

upstream backend {
    ip_hash;
    server backend1.example.com;
    server backend2.example.com;
}

server {
    listen 80;

    location / {
        proxy_pass http://backend;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
    }
}

Here, ip_hash ensures that requests from the same IP are directed to the same server, which approximately corresponds to user routing.

For more precise user routing, it is necessary to analyze identifiers in requests and configure the load balancer or proxy accordingly.