docker compose scale two services as group

Question

I'm new to Docker compose and looking for a way to scale two services together at the same time and set an environments for each replica.

This docker-compose example for what I want to achieve

version: '3'

networks:
  my-network:
    ipam:
      driver: default
      config:
        - subnet: 172.20.0.0/16

services:
  my-service:
    image: service:latest
    networks:
      - my-network
  my-client:
    image: client:latest
    depends_on:
      - my-service
    networks:
      - my-network
    environment:
      SERVICE_IP: "my-service:1234"

when I run this with docker-compose -f docker-compose.test.yml up everything works fine.

Now I want to scale the two services such that every my-client has one unique my-service, I tried to do docker-compose -f docker-compose.test.yml up --scale my-service=10 --scale my-client=10

What happened is some of the my-client has the same my-service IP because of SERVICE_IP: "my-service:1234" and didn't uniquely assign the IP's as one to one. which left some my-service without any client and some my-service witch many clients.

My current workaround

since docker compose create services when scale which has names like <service_name>#, I try to do reverse DNS lookup for each my-client to match with one my-service

version: '3'

networks:
  my-network:
    ipam:
      driver: default
      config:
        - subnet: 172.20.0.0/16

services:
  my-service:
    image: service:latest
    networks:
      - my-network
  my-client:
    image: client:latest
    depends_on:
      - my-service
    networks:
      - my-network
    command: sh -c "export MY_IP=$$(ifconfig | grep '172.20' | awk '{print $$2}' | cut -d ':' -f2) && export MY_SERVICE=$$(host $$MY_IP | awk '{print $$5}' | cut -d '.' -f1 | sed 's/my-client/my-serivce/g') && export SERVICE_IP=$$MY_SERVICE:1234 && my-client

I removed SERVICE_IP: "my-service:1234" and got my-client domainname using reverse DNS, then replace my-client from the domain to my-service which will map one client for one service.

inspired by: https://stackoverflow.com/a/64790547/14053770

TL;TR

I want to assign environments with a service name,container name, ... that can scale uniquely as group one to one, without this workaround.

docker compose scale two services as group

0 Answers0