Connecting containers to multiple networks in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to create a Docker network named 'frontend'.

Docker

docker network create [1]

Drag options to blanks, or click blank then click option'

Afrontend

Bbackend

Cdefault

Dbridge

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'bridge' creates the default network, not a custom one.

Using 'backend' creates a different network name.

The command docker network create frontend creates a new network named 'frontend'.

2fill in blank

medium

Complete the command to run a container named 'webapp' attached to the 'frontend' network.

Docker

docker run -d --name webapp --network [1] nginx

Drag options to blanks, or click blank then click option'

Abackend

Bhost

Cdefault

Dfrontend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'backend' connects to the wrong network.

Using 'host' connects to the host network, not a Docker network.

The --network frontend option connects the container to the 'frontend' network.

3fill in blank

hard

Fix the error in the command to connect the running container 'webapp' to the 'backend' network.

Docker

docker network connect [1] webapp

Drag options to blanks, or click blank then click option'

Abackend

Bwebapp

Cfrontend

Ddefault

Attempts:

3 left

💡 Hint

Common Mistakes

Using the container name instead of the network name first.

Using 'frontend' instead of 'backend'.

The correct command is docker network connect backend webapp to connect the container to the 'backend' network.

4fill in blank

hard

Fill both blanks to list all networks a container named 'db' is connected to.

Docker

docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}} [1] {{end}}' [2]

Drag options to blanks, or click blank then click option'

A.NetworkID

Bdb

C.IPAddress

Dwebapp

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong property like '.NetworkID' which is not directly accessible.

Using the wrong container name.

The command uses .IPAddress to show IP addresses of networks connected to the container named 'db'.

5fill in blank

hard

Fill all three blanks to create a container 'app' connected to 'frontend' and then connect it to 'backend'.

Docker

docker run -d --name [1] --network [2] nginx && docker network connect [3] [1]

Drag options to blanks, or click blank then click option'

Aapp

Bfrontend

Cbackend

Dwebapp

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing container names and network names.

Using 'webapp' instead of 'app'.

This sequence runs a container named 'app' on the 'frontend' network, then connects it to the 'backend' network.

Practice

1. What is the main benefit of connecting a Docker container to multiple networks?

easy

A. It increases the container's CPU usage automatically.

B. It makes the container run faster by using multiple networks.

C. It allows the container to communicate with different isolated groups of containers.

D. It automatically backs up container data across networks.

Solution

1. Step 1: Understand Docker networks

   Docker networks isolate groups of containers so they can communicate securely within the group.

2. Step 2: Multiple networks allow multi-group communication

   Connecting a container to multiple networks lets it talk to containers in each network separately.

3. Final Answer:

   It allows the container to communicate with different isolated groups of containers. -> Option C

4. Quick Check:

   Multiple networks = multi-group communication [OK]

Hint: Multiple networks let containers talk to separate groups [OK]

Common Mistakes:

• Thinking multiple networks speed up container
• Assuming multiple networks backup data
• Believing CPU usage increases automatically

2. Which Docker command correctly connects an existing container named webapp to a network called frontend?

easy

A. docker network add webapp frontend

B. docker connect network webapp frontend

C. docker container network add webapp frontend

D. docker network connect frontend webapp

Solution

1. Step 1: Recall Docker network connect syntax

   The correct syntax is docker network connect [network] [container].

2. Step 2: Match command to syntax

   docker network connect frontend webapp matches the syntax exactly: docker network connect frontend webapp.

3. Final Answer:

   docker network connect frontend webapp -> Option D

4. Quick Check:

   docker network connect = correct syntax [OK]

Hint: Use 'docker network connect [network] [container]' syntax [OK]

Common Mistakes:

• Swapping network and container order
• Using 'docker connect network' which is invalid
• Trying to add network with 'docker network add'

3. Given the commands below, what networks will the container db be connected to?

docker network create backend
docker network create monitoring

docker run -d --name db --network backend postgres

docker network connect monitoring db

medium

A. Only backend

B. Both backend and monitoring

C. Only monitoring

D. No networks connected

Solution

1. Step 1: Analyze initial container network

   The container db is started with --network backend, so it connects to backend first.

2. Step 2: Analyze network connect command

   The command docker network connect monitoring db adds monitoring network to the same container.

3. Final Answer:

   Both backend and monitoring -> Option B

4. Quick Check:

   Initial network + connect command = multiple networks [OK]

Hint: Initial network + connect command = multiple networks [OK]

Common Mistakes:

• Assuming second connect replaces first network
• Thinking container can only have one network
• Ignoring the network connect command

4. You tried to connect a container app to a network frontend using docker network connect frontend app, but got an error: Error response from daemon: network frontend not found. What is the most likely cause?

medium

A. The network frontend does not exist.

B. The container app is not running.

C. You used the wrong command syntax.

D. Docker daemon is not running.

Solution

1. Step 1: Understand the error message

   The error says network frontend not found, meaning Docker cannot find a network named frontend.

2. Step 2: Check possible causes

   If the network does not exist, the connect command fails. Container running state or syntax errors produce different messages.

3. Final Answer:

   The network frontend does not exist. -> Option A

4. Quick Check:

   Error 'network not found' = missing network [OK]

Hint: Check network existence if 'network not found' error appears [OK]

Common Mistakes:

• Assuming container must be running for connect
• Blaming command syntax without checking network
• Ignoring Docker daemon status

5. You have two networks: frontend and backend. You want a container api to be initially connected to frontend and communicate with containers in both networks but keep traffic isolated. Which sequence of commands correctly sets this up?

hard

A. docker network create frontend

docker network create backend

docker run -d --name api --network frontend myapi

docker network connect backend api

B. docker network create frontend

docker network create backend

docker run -d --name api --network backend myapi

docker network connect frontend api

C. docker network create frontend

docker network create backend

docker run -d --name api myapi

docker network connect frontend api

docker network connect backend api

D. docker network create frontend

docker network create backend

docker run -d --name api --network frontend --network backend myapi

Solution

1. Step 1: Create both networks

   Commands docker network create frontend and docker network create backend create the two isolated networks.

2. Step 2: Start container on one network and connect to the other

   Start api on frontend network, then connect it to backend using docker network connect backend api. This keeps traffic isolated but allows communication on both.

3. Final Answer:

   docker network create frontend docker network create backend docker run -d --name api --network frontend myapi docker network connect backend api -> Option A

4. Quick Check:

   Start on one network + connect second = multiple isolated networks [OK]

Hint: Start container on one network, then connect to others [OK]

Common Mistakes:

• Trying to specify two --network flags in docker run
• Not connecting container to second network after start
• Starting container without any network