I have a couple of app containers that I want to connect to the mongodb container. I tried with external_links but I can not connect to the mongodb.
I get
MongoError: failed to connect to server [mongodb:27017] on firstconnect
Do I have to add the containers into the same network to get external_links working?
MongoDB:
version: '2'services:mongodb:image: mongo:3.4restart: alwaysports:- "27017:27017"volumes:- data:/data/dbvolumes:data:App:
version: '2'services:app-dev:restart: Alwaysbuild: repository/ports:- "3000:80"env_file:- ./environment.envexternal_links:- mongodb_mongodb_1:mongodbNetworks:
# sudo docker network lsNETWORK ID NAME DRIVER SCOPE29f8bae3e136 bridge bridge local67d5519cb2e6 dev_default bridge local9e7097c844cf host host local481ee4301f7c mongodb_default bridge local4275508449f6 none null local873a46298cd9 prod_default bridge localBest Answer
Documentation at https://docs.docker.com/compose/compose-file/#/externallinks says
If you’re using the version 2 file format, the externally-created containers must be connected to at least one of the same networks as the service which is linking to them.Ex:
Create a new docker network
docker network create -d bridge custom
docker-compose-1.yml
version: '2'services:postgres:image: postgres:latestports:- 5432:5432networks:- customnetworks:custom:external: truedocker-compose-2.yml
version: '2'services:app:image: training/webappnetworks:- customexternal_links:- postgres:postgresnetworks:custom:external: trueYuva's answer above for the version 2 holds good for version 3 as well.
The documentation for the external_links isn't clear enough.
For more clarity I pasted the version 3 variation with annotation
version: '3'services:app:image: training/webappnetworks:- <<network created by other compose file>>external_links:- postgres:postgresnetworks:<<network created by other compose file>>:external: trueRecently I faced Name resolution failure trying to link 2 containers handled by docker-compose v3 representing gRPC server and client in my case, but failed and with external_links.
I'll probably duplicate some of the info posted here, but will try to summarize as all these helped me solving the issue.
From external_links docs (as mentioned in earlier answer):
If you’re using the version 2 or above file format, the externally-created containers must be connected to at least one of the same networks as the service that is linking to them.
The following configuration solved the issue.
project-grpc-server/docker-compose.yml
version: '3'services:app:networks:- some-networknetworks:some-network:Server container configured as expected.
project-grpc-client/docker-compose.yml
services:app:external_links:# Assigning easy alias to the target container- project-grpc-server_app_1:servernetworks:# Mentioning current container as a part of target network- project-grpc-server_some-networknetworks:# Announcing target network (where server resides)project-grpc-server_some-network:# Telling that announced network already exists (shouldn't be created but used)external: trueWhen using defaults (no container_name configured) the trick with configuring client container is in prefixes. In my case network name had prefix project-grpc-server_ when working with docker-compose and than goes the name itself some-network (project-grpc-server_some-network). So fully qualified network names should be passed when dealing with separate builds.
While container name is obvious as it appears from time to time on the screen the full network name is not easy-to-guess candidate when first facing this section of Docker, unless docker network ls.
I'm not a Docker expert, so please don't judge too strict if all this is obvious and essential in Docker world.