What is the difference between docker-compose ports vs expose

Question

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

Answer 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)

Answer 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