Docker Compose: expose with scaling-CodePudding

I scale container

  ports:
  - "8086-8090:8085"

But what if I needed it only inside my bridge network? In other words, does it exists something like this?

  expose:
  - "8086-8090:8085"

UPDATED: I have a master container:

exposed to host network
acts as a load balancer

I want to have N slaves of another container, exposed to assigned ports inside docker network (bot visible in host network)

CodePudding user response：

Connections between containers (over the Docker-internal bridge network) don't need ports: at all, and you can just remove that block. You only need ports: to accept connections from outside of Docker. If the process inside the container is listening on port 8085 then connections between containers will always use port 8085, regardless of what ports: mappings you have or if there is one at all.

expose: in a Compose file does almost nothing at all. You never need to include it, and it's always safe to delete it.

(This wasn't the case in first-generation Docker networking. However, Compose files v2 and v3 always provide what the Docker documentation otherwise calls a "user-defined bridge network", that doesn't use "exposed ports" in any way. I'm not totally clear why the archaic expose: and links: options were kept.)

CodePudding user response：

No extra changes needed!

Because of internal Docker DNS it 'hides' scaled instances under same port:

  version : "3.8"
  services:
    web:
      image: "nginx:latest"
      ports:
      - "8080:8080"

then

docker-compose up -d --scale web=3

calling localhost:8080 will proxy requests to all instances using Round Robin!