What is Upstream Block in Nginx: Explanation and Example

The upstream block in Nginx defines a group of backend servers that Nginx can proxy requests to. It is mainly used to load balance traffic across multiple servers or services, improving reliability and performance.

How It Works

The upstream block acts like a traffic controller for Nginx. Imagine you have several identical restaurants (servers) and many customers (requests) arriving. Instead of sending all customers to one restaurant, the traffic controller directs each customer to a different restaurant to avoid crowding.

In Nginx, the upstream block lists backend servers by their addresses. When a user makes a request, Nginx picks one server from this list based on a load balancing method (like round-robin). This helps spread the work evenly and keeps the service fast and available.

Example

This example shows an upstream block named backend_servers with two servers. The server block uses this group to proxy requests.

nginx

upstream backend_servers {
    server 192.168.1.10:8080;
    server 192.168.1.11:8080;
}

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

Output

When a client requests the Nginx server on port 80, Nginx forwards the request to either 192.168.1.10:8080 or 192.168.1.11:8080, alternating between them.

When to Use

Use the upstream block when you want to distribute incoming traffic across multiple backend servers. This is helpful to:

• Improve performance by balancing load
• Increase reliability by having backups if one server fails
• Scale your application horizontally by adding more servers

Common real-world cases include web applications, APIs, or microservices where multiple instances run behind a single Nginx proxy.

Key Points

• The upstream block groups backend servers for load balancing.
• Nginx uses this block to proxy requests to multiple servers.
• It supports different load balancing methods like round-robin and least connections.
• Improves availability and scalability of applications.

Key Takeaways

The upstream block defines backend servers for Nginx to proxy requests.

It enables load balancing to distribute traffic evenly across servers.

Use it to improve application performance, reliability, and scalability.

You configure proxy_pass to point to the upstream group.

Supports multiple load balancing methods like round-robin and least connections.