Docker compose port mapping

Question

I have a docker-compose yml file as in below

version: '2' services:   nodejs:     build:       context: .       dockerfile: DockerFile     ports:       - "4000:4000"     links:       - redis     expose:       - "6379"   redis:     build:       context: .       dockerfile: Dockerfile-redis 

My goal is to forward nodejs-127.0.0.1 port 6379 to the redis host. I can already ping redis from the nodejs machine, but the ports are not mapped. Tried expose options, but no chance either.

Answer 1

If you want to bind to the redis port from your nodejs container you will have to expose that port in the redis container:

version: '2' services:   nodejs:     build:       context: .       dockerfile: DockerFile     ports:       - "4000:4000"     links:       - redis    redis:     build:       context: .       dockerfile: Dockerfile-redis     expose:       - "6379" 

The expose tag will let you expose ports without publishing them to the host machine, but they will be exposed to the containers networks.

https://docs.docker.com/compose/compose-file/#expose

The ports tag will be mapping the host port with the container port HOST:CONTAINER

https://docs.docker.com/compose/compose-file/#ports

Answer 2

It's important to point out that all of the above solutions map the port to every interface on your machine. This is less than desirable if you have a public IP address, or your machine has an IP on a large network. Your application may be exposed to a much wider audience than you'd hoped.

redis:   build:     context:     dockerfile: Dockerfile-redis     ports:     - "127.0.0.1:3901:3901" 

127.0.0.1 is the ip address that maps to the hostname localhost on your machine. So now your application is only exposed over that interface and since 127.0.0.1 is only accessible via your machine, you're not exposing your containers to the entire world.

The documentation explains this further and can be found here: https://docs.docker.com/compose/compose-file/#ports

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Note: If you're using Docker for mac this will make the container listen on 127.0.0.1 on the Docker for Mac VM and will not be accessible from your localhost. If I recall correctly.