Localhost and docker-compose networking issue

[dmaze (David Maze)]

@jeremypumphrey

Now that Docker for Mac uses localhost instead of an IP, should communication between docker containers and non-docker containers be possible using localhost for all?

localhost always (every platform, every Docker setup) refers to the container itself and never to anything running in any other container or the host system. (Unless you’re running a container with --net host, which is odd on Docker for Mac.)

On every platform with every Docker setup, if you can identify a “real” IP address for the host system, you can use it to connect to services that are running there, including other Docker containers that publish ports with docker run -p. Some platforms/setups provide a bridge address that you can use to access the host system (frequently 172.17.0.1/16 on native Linux and 192.168.99.100/24 on Docker Toolbox/Docker Machine) but Docker for Mac does not have this.

1. Cross-container networking: Can the containers call each other by localhost:port (localhost:8000 for example) or can they only use the compose name like dynamodb:8000?

localhost always refers to the current container. You have to use the compose name.

2. Cross-system networking: Can the non-docker services running locally use the db at localhost:8000?

Since you declare that as a published port with a Docker Compose ports section, yes.