将随机端口暴露给 docker-compose.yml

Question

I need multiple instance of same application, for that I am using server.port=0 to run application in random port. my question is how can I map randomly generated port to docker-compose.yml to create multiple instances. I am using spring boot at the back-end. I am unable to find any solution. Any help much appreciated.

Answer 1

Each Docker container runs a single process in an isolated network namespace, so this isn't necessary. Pick a fixed port. For HTTP services, common port numbers include 80, 3000, 8000, and 8080, depending on permissions and the language runtime (80 requires elevated privileges, 3000 is Node's default, and so on). The exact port number doesn't matter.

You access the port from outside Docker space using a published port. If you're running multiple containers, there is the potential for conflict if multiple services use the same host port, which is probably what you're trying to avoid. In the docker run -p option or the Docker Compose ports: setting, it's possible to list only the port running inside the container, and Docker will choose a host port for you.

version: "3"
services:
  web:
    image: ...
    ports:
      - "8000"                       # no explicit host port
    command: ... -Dserver.port=8000  # fixed container port

docker-compose port web 8000 will tell you what the host (public) port number is. For communication between containers in the same docker-compose.yml file, you can use the service name and the (fixed, known) internal port, http://web:8000 .