Final test: Containers: Docker and compose

Read the output

Both containers were started without --network. Why can't app find db?

$ sudo docker ps --format '{{.Names}} {{.Status}}'
app Up 2 minutes
db Up 2 minutes
$ sudo docker logs --tail 1 app
app: db unreachable: nc: bad address 'db'

• A db has no -p 5432:5432.
• B db is not listening on port 5432.
• C Containers on the default network cannot see each other at all.
• D Nobody resolves container names on the default network — app asks the host's DNS servers.