Dynamic Upstream learning

Just playing with some NGINX lua balancing features

Motivation

I wanted to learn more about how to balance requests to upstreams in a more dynamic way. What if I need to route some requests to one upstream A, and some other requests to upstream B.

Problem

You have given the task of balancing requests. If a request with /foo/something comes in you need to balance the requests between to server A (primary) and pick the server B (backup) when A does not work.

Ok, it could be a static upstream in NGINX, right? Yes, you are right but rabbits don't come easy.

Servers come and go, and we need to be ready to deliver different hosts for different requests.

sequenceDiagram
    participant User
    participant NGINX
    participant Server1 as 127.0.0.2
    participant Server2 as 127.0.0.3

    User->>NGINX: Request /foo/something
    NGINX->>Server1: Proxy Pass
    Server1->>NGINX: Success Response
    NGINX->>User: Forward Success Response

    User->>NGINX: Request /foo/something
    NGINX->>Server1: Proxy Pass
    Server1-->>NGINX: Failure Response
    NGINX->>Server2: Proxy Pass
    Server2->>NGINX: Success Response
    NGINX->>User: Forward Success Response

Loading

Running

Dependencies:

• just
• docker compose

$ just -l

Available recipes:
    rebuild # Rebuild all containers
    reload  # Reload NGINX
    run     # Start origin and upstreams API
    stop    # Stop origin and upstreams API

$ just run

Now you have NGINX running on 8080 and upstreams API on 8081.

Go ahead and make a request for an existing upstream:

curl -v http://localhost:8080/upstream1/foo

Then for an upstream that does not exist:

curl -v http://localhost:8080/upstream2/foo

Compare the logs and the HTTP responses.