Good morning,
sorry for confusing you.
I meant it this way:
remove the lines
extra_hosts:
- "host.docker.internal:host-gateway"
from your docker-compose.yml
replace the lines
external_links: - mongo
by
links: - mongo
within your docker-compose.yml’s app-section because you want to connect to a container defined within the same docker-compose.yml
To connect to the mongo-container from app-container use the hostname mongo
To connect to your host’s localhost from within a container use 172.17.0.1 (as you are running on Linux). It would be host.docker.internal if you running Docker on Windows.