Load Balancers: The Traffic Controller of Your Backend

Once one application server is no longer enough, we can run multiple copies of the application.

But this creates another question:

Which server should receive each request?

A load balancer solves this problem.

Clients communicate with one stable endpoint while the load balancer distributes requests across healthy servers.

What Does a Load Balancer Do?

Common responsibilities include:

• distributing traffic,
• checking server health,
• terminating TLS,
• routing based on host or path,
• removing unhealthy servers,
• draining traffic during deployment.

Round Robin

Request 1 → Server A
Request 2 → Server B
Request 3 → Server C
Request 4 → Server A

Least Connections

If requests have different durations, the load balancer can prefer the server handling the fewest active connections.

Health Checks

GET /health/ready

200 OK

Horizontal scaling becomes easier when application servers do not rely on local memory for important shared state.