Automatically append docker container to upstream config of nginx load balancer

Question

I'm running Docker Compose (v2) and have a node service (website) and python based api deployed with nginx sitting in front of them.

One thing I would like to do is be able to scale the services by adding more containers. If I know ahead of time how many containers I will have, I can hardcode the nginx upstream config with the references to the IPs of the containers which docker makes available. However, the problem is that I want the upstream nginx config to be dynamic e.g. if I add another Docker container, it simply adds appends the location of the container to the upstream list of IPs in the upstream block.

My idea was to create a script which will automatically append the upstream servers using env variables when the containers change but I'm unsure where to start and can't find a good example.

Answer 1

There are a couple ways to achieve this. What you are referring to is usually called service discovery and comes in many forms. I'll describe two of them that I have used before.

The first and simplest one (which works fine for single servers or only discovering containers locally on one server) is a local proxy which makes use of the Docker socket or API. https://github.com/jwilder/nginx-proxy is one of the popular ones and should work well for prototyping scalable services in Compose.

Another way (which is more multi-host friendly but more complicated) would be registering services in a registry (such as etcd or Consul) and then dynamically writing out the configuration. To do this, you can use a registration system (such as https://github.com/gliderlabs/registrator) to register the containers and their ports. Then your proxy or application can consume a configuration file written out using a template system like https://github.com/kelseyhightower/confd.