Connecting to docker mongo db image

Question

I'm trying to use these instructions to try to run the mongodb docker image in a container.

I'm able to run the image:

(virtual) anonymous@anonymous:~/PycharmProjects/PostDekko/climbticks-flaskmongoangul$ sudo docker container ls
CONTAINER ID        IMAGE                                COMMAND                  CREATED             STATUS              PORTS                    NAMES
431a9d693f48        mongo:bionic                         "docker-entrypoint.s…"   24 minutes ago      Up 24 minutes       27017/tcp                climbticks-mongodb
f12d227dcdd8        climbticks-flaskmongoangul_web_dev   "python3.8 index.py"     3 hours ago         Up 3 hours          0.0.0.0:4000->4000/tcp   climbticks-flaskmongoangul_web_dev_1

My project is in the 2nd container, and the mongodb image is container_id 431a9d693f48. I can also access the logs, so I know it runs.

From their instructions:

The MongoDB server in the image listens on the standard MongoDB port, 27017, so connecting via Docker networks will be the same as connecting to a remote mongod. The following example starts another MongoDB container instance and runs the mongo command line client against the original MongoDB container from the example above, allowing you to execute MongoDB statements against your database instance:

> $ docker run -it --network some-network --rm mongo mongo --host
> some-mongo test

... where some-mongo is the name of your original mongo container.

However.... I don't understand what my "network" is supposed to be. I think that the network argument, from docker's perspective, means a network id. If I run:

(virtual) anonymous@anonymous:~/PycharmProjects/PostDekko/climbticks-flaskmongoangul$ sudo docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
7fbed634dbdf        bridge              bridge              local
0843e5ae6173        host                host                local
6b3c8eb4b216        none                null                local
cc3d76f1f109        web_dev             bridge              local

I get 4 network ids. web_dev is my project's (webserver) container. If I try any of the 4, I get:

(virtual) anonymous@anonymous:~/PycharmProjects/PostDekko/climbticks-flaskmongoangul$ sudo docker run -it --network cc3d76f1f109 --rm mongo mongo --host climbticks-mongodb test
MongoDB shell version v4.2.7
connecting to: mongodb://climbticks-mongodb:27017/test?compressors=disabled&gssapiServiceName=mongodb
2020-05-31T01:55:08.771+0000 E  QUERY    [js] Error: couldn't connect to server climbticks-mongodb:27017, connection attempt failed: HostNotFound: Could not find address for climbticks-mongodb:27017: SocketException: Host not found (authoritative) :
connect@src/mongo/shell/mongo.js:341:17
@(connect):2:6
2020-05-31T01:55:08.779+0000 F  -        [main] exception: connect failed
2020-05-31T01:55:08.779+0000 E  -        [main] exiting with code 1

I also tried various expressions for localhost (0.0.0.0, localhost, etc.) even though that didn't make sense to me.

So.... how do I find what the network is supposed to be?

EDIT: although if I connect to my DB in the shell:

sudo docker exec -it climbticksmongodb bash

then I can talk to it. So the DB is live. I really just need to figure the network issue, it seems.

Answer 1

When you start a container, it starts in the default bridge network, so without specifying any network attached to your containers, they will not be able to connect to each other.

There are several ways to make them interact with each other. You could create a network and then attach both of them.

For example:

docker network create -d bridge my-bridge-network

Then attach it with --network my-bridge-network to both docker run commands.

Or attach it to a running container with docker <container> attach <network>

This is also a problem docker-compose fixes, you are able to run various containers with the same network attached.

Another method is to use the special DNS host.docker.internal which is essentially the containers host localhost. So if you do a docker run mongo -p 27017:27017 and you want to connect in another container you can connect to host.docker.internal:27017 which is your port 27017 bind to the mongo container 27017.

More detailed information on docker documentation:

https://docs.docker.com/network/network-tutorial-standalone/