Docker-compose with Loopback and Mongodb fail to c

Question

I have been learning docker lately and I was unable to make a connection between my loopback api and mongodb. The application works fine in local dev environment. With docker-compose my mongodb server runs at localhost:27017 and my react-frontend serves at localhost:3000 and looks fine. Only loopback is unable to connect to mongodb and throws the following errors:

loopback_1  | Web server listening at: http://localhost:8080
loopback_1  | Browse your REST API at http://localhost:8080/explorer
loopback_1  | Connection fails: MongoError: failed to connect to server 
[localhost:27017] on first connect [MongoError: connect ECONNREFUSED 
127.0.0.1:27017]
loopback_1  | It will be retried for the next request.
loopback_1  | 
loopback_1  | /opt/src/app/node_modules/mongodb/lib/mongo_client.js:421
loopback_1  |           throw err
loopback_1  |           ^
loopback_1  | MongoError: failed to connect to server [localhost:27017] 
on first connect [MongoError: connect ECONNREFUSED 127.0.0.1:27017]
loopback_1  |     at Pool.<anonymous> 
(/opt/src/app/node_modules/mongodb-core/lib/topologies/server.js:336:35)

Here is my Dockerfile for Loopback-API

FROM node:6

RUN mkdir -p /opt/src/app

WORKDIR  /opt/src/app

COPY package.json /opt/src/app

RUN npm cache clean

RUN npm install

COPY . /opt/src/app

EXPOSE 8080

CMD ["npm", "start"]

My docker-compose file looks like this:

    version: '3.0' # specify docker-compose version

# Define the services/containers to be run
services:
  database: # name of first service
      image: mongo # specify the image to build container from
      ports:
        - "27017:27017" # specify port forwarding

  loopback: # name of second service
      build: myapp_backend # specify the directory of the Dockerfile
      ports:
        - "8080:8080" # specify port mapping
      links:
        - database # link this service to the database service

  react: # name of third service
      build: myapp_frontend # specify the directory of the Dockerfile
      ports:
        - "3000:3000" #specify port mapping

And finally datasource file in loopback-api looks like this:

    {
  "db": {
    "host": "localhost",
    "port": 27017,
    "url": "",
    "database": "test",
    "password": "",
    "name": "mongoDS",
    "user": "",
    "connector": "mongodb"
  }
}

Answer 1

Your datasource file should have:

"host": "database" ...

since in docker-compose.yml you link mongo container to loopback as database, so it's not localhost. Remember, you are trying to connect to mongo from loopback docker container. Also you should make sure that mongo is started before loopback, so add depends_on: database to loopback service in docker-compose.yml.