App in docker container cannot access localhost database in other container

I run a mongodb in docker container with

docker run -p 127.0.0.1:27017:27017 -v /data/db:/data/db --name mongodb -d --rm mongo:3.4

and docker ps:

da5789a63e57  mongo:3.4  "/entrypoint.sh --..."  18 hours ago  Up 18 hours  127.0.0.1:27017->27017/tcp  mongodb

then I run my app with --link:

docker run -p 3000:3000 -v /data/app:/data/app --rm --name app --link mongodb:mongo <IMAGE>

and docker ps:

b033802795fc  brickyang/contest:1.1.0  "pm2 start --no-da..."  4 seconds ago  Up 3 seconds  127.0.0.1:3000->3000/tcp  app

There's no link name like mongo/app as expected, and the app always throw an error about:

MongoError: failed to connect to server [localhost:27017] on first connect

If I start the app locally with npm start(mongo in container), it works great.

via Brick Yang