What is the difference between docker-compose ports vs expose

What is the difference between ports and expose options in docker-compose.yml?

Solution 1:

According to the docker-compose reference,

Ports is defined as:

Expose ports. Either specify both ports (HOST:CONTAINER), or just the container port (a random host port will be chosen).

• Ports mentioned in docker-compose.yml will be shared among different services started by the docker-compose.
• Ports will be exposed to the host machine to a random port or a given port.

My docker-compose.yml looks like:

mysql:
  image: mysql:5.7
  ports:
    - "3306"

If I do docker-compose ps, it will look like:

  Name                     Command               State            Ports
-------------------------------------------------------------------------------------
  mysql_1       docker-entrypoint.sh mysqld      Up      0.0.0.0:32769->3306/tcp

Expose is defined as:

Expose ports without publishing them to the host machine - they’ll only be accessible to linked services. Only the internal port can be specified.

Ports are not exposed to host machines, only exposed to other services.

mysql:
  image: mysql:5.7
  expose:
    - "3306"

If I do docker-compose ps, it will look like:

  Name                  Command             State    Ports
---------------------------------------------------------------
 mysql_1      docker-entrypoint.sh mysqld   Up      3306/tcp

Edit

In recent versions of Dockerfile, EXPOSE doesn't have any operational impact anymore, it is just informative. (see also)

Solution 2:

ports:

1. Activates the container to listen for specified port(s) from the world outside of the docker(can be same host machine or a different machine) AND also accessible world inside docker.
2. More than one port can be specified (that's is why ports not port)

expose:

1. Activates container to listen for a specific port only from the world inside of docker AND not accessible world outside of the docker.
2. More than one port can be specified