Connecting to mongo from a different container - connection refused - mongodb

Question

I'm trying to create a docker file that mongo running in a different container, to execute commands from a file, however the second container receives a connection refused error:
mongo-testdata_1 | MongoDB shell version: 3.2.9
mongo-testdata_1 | connecting to: mongo:27017/admin
mongo-testdata_1 | 2019-12-15T15:57:30.067+0000 W NETWORK [thread1] Failed to connect to 127.0.0.1:27017, reason: errno:111 Connection refused
mongo-testdata_1 | 2019-12-15T15:57:30.067+0000 E QUERY [thread1] Error: couldn't connect to server 127.0.0.1:27017, connection attempt failed :
mongo-testdata_1 | #./testData.js:1:20
mongo-testdata_1 |
mongo-testdata_1 | failed to load: ./testData.js
How would I be able to connect to the mongoDB running on the first container, using the mongo cli in the second?
commands used
docker-compose up -d mongo
docker exec my-test-mongo mongo --eval "db.createUser({ user: 'admin', pwd: 'password', roles: [ 'dbAdmin', 'readWrite' ] });" admin
docker-compose up --build mongo-testdata
mongo.dockerfile
FROM mongo:3.2.9
ADD testData.js .
ENTRYPOINT ["mongo"]
docker-compose.yml
version: '2'
services:
mongo-testdata:
build:
context: .
dockerfile: mongo.dockerfile
command: --host mongo --port 27017 --username='admin' --password='password' admin ./testData.js
depends_on:
- mongo
networks:
- backend
mongo:
image: mongo:3.2.9
container_name: my-test-mongo
ports:
- 27017:27017
networks:
- backend
networks:
backend:
driver: bridge
testData.js
const myDb = new Mongo().getDB('mydb');
myDb.getCollection('test').insert({
foo: 'bar',
});

Answer 1

You need to specify host and port when you connect to mongo in testData.js.
new Mongo(<host:port>)
In your case this would be new Mongo('mongo').
https://docs.mongodb.com/v3.2/reference/method/Mongo/#Mongo
Instantiation Options
Use the constructor without a parameter to instantiate a connection to the localhost interface on the default port.
Pass the parameter to the constructor to instantiate a connection to the and the default port.
Pass the <:port> parameter to the constructor to instantiate a connection to the and the .

Answer 2

The only depends_on will not work, as the mongo DB container process is not ready to accept to container while CLI get connection refused. You can try two option
- simply put sleep for some second the DB container will ready to accept connection
- Increase wait timeout in mongo shell connection
Here is way to deal with connection refused by adding 10 second seelp in import.
version: '2'
services:
mongo_import:
image: mongo
command: /bin/bash -c "sleep 10 && mongo --host mongo --port 27017 --username='admin' --password='password' admin /root/testData.js"
volumes:
- ./testData.js:/root/testData.js
depends_on:
- mongo
mongo:
image: mongo
container_name: my-test-mongo
ports:
- 27017:27017
Btw the above task you can perform in the same container without the need of any cli container.
Initializing a fresh instance
When a container is started for the first time it will execute files
with extensions .sh and .js that are found in
/docker-entrypoint-initdb.d. Files will be executed in alphabetical
order. .js files will be executed by mongo using the database
specified by the MONGO_INITDB_DATABASE variable, if it is present, or
test otherwise. You may also switch databases within the .js script.
Initializing a fresh instance