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dockerdocker-composedocker-network

Docker Mapping Same Port On Two Containers To Different Ports On Host

I have the following docker-compose setup:

db:
  image: postgres:10.5-alpine

adminer:
  image: adminer:4.6.3
  ports:
    - 8080:8086

my-service:
  image: my-image:latest
  ports:
    - 8080:8080

When I run docker-compose up, I get the following error:

ERROR: for adminer  Cannot start service adminer: driver failed programming
  external connectivity on endpoint docker_adminer_1
  (dcd0d56d58bbbefdea89dc64532854597fcaec9736d7ddb3f8de74bc1577d5ee):
  Bind for 0.0.0.0:8080 failed: port is already allocated

I must be misunderstanding docker networking. I thought because, I'm mapping the 8080 port on the two services to different host ports viz. 8080 and 8086, I thought I shouldn't have conflicts. I can't seem to be able to locate the relevant documentation on the web.

Can you guys please help me remedy this situation?

Thanks!

Solution

  • You have it backwards.

    <host_port>:<service_port> and not the other way around. Switch the numbers and you ought to be fine, but make sure your services are expecting traffic on those new ports.

    Edit: documentation