Network isolation between services in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new Docker network named 'isolated_net'.

Docker

docker network create [1]

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

Aisolated_net

Bbridge

Chost

Dnone

Attempts:

3 left

💡 Hint

Common Mistakes

Using default network drivers like 'bridge' instead of a custom name.

Confusing network driver names with network names.

The command docker network create isolated_net creates a new isolated network named 'isolated_net'.

2fill in blank

medium

Complete the command to run a container named 'webapp' connected to the 'isolated_net' network.

Docker

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

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

Aisolated_net

Bnone

Chost

Dbridge

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'bridge' network instead of the custom 'isolated_net'.

Omitting the --network option.

The --network isolated_net option connects the container to the isolated network.

3fill in blank

hard

Fix the error in the command to disconnect a container named 'db' from the 'isolated_net' network.

Docker

docker network [1] isolated_net db

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

Aremove

Bdisconnect

Cconnect

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'connect' instead of 'disconnect'.

Using 'remove' or 'delete' which are invalid for this command.

The correct command to disconnect a container from a network is docker network disconnect.

4fill in blank

hard

Fill both blanks to create a Docker Compose service named 'api' that uses the 'isolated_net' network and exposes port 5000.

Docker

services:
  api:
    image: myapi
    ports:
      - "[1]:5000"
    networks:
      - [2]

networks:
  isolated_net:
    driver: bridge

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

A5000

Bisolated_net

C80

Ddefault

Attempts:

3 left

💡 Hint

Common Mistakes

Using container port instead of host port in ports mapping.

Using 'default' network instead of 'isolated_net'.

Port mapping uses the host port 5000 to map to container port 5000. The network name is 'isolated_net' to ensure isolation.

5fill in blank

hard

Fill all three blanks to define a Docker Compose file with two services 'frontend' and 'backend' isolated on 'isolated_net' network, where 'frontend' depends on 'backend'.

Docker

services:
  frontend:
    image: myfrontend
    depends_on:
      - [1]
    networks:
      - [2]
  backend:
    image: mybackend
    networks:
      - [3]

networks:
  isolated_net:
    driver: bridge

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

Abackend

Bfrontend

Cisolated_net

Ddefault

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping 'frontend' and 'backend' in depends_on.

Using 'default' network instead of 'isolated_net'.

'frontend' depends on 'backend', and both services use the 'isolated_net' network for isolation.

Practice

1. What is the main purpose of network isolation between Docker services?

easy

A. To keep services separate and control their communication

B. To speed up container startup time

C. To reduce the size of Docker images

D. To automatically update containers

Solution

1. Step 1: Understand network isolation concept

   Network isolation means keeping services separate so they don't communicate unless allowed.

2. Step 2: Identify the main goal

   The main goal is to control communication and improve security between services.

3. Final Answer:

   To keep services separate and control their communication -> Option A

4. Quick Check:

   Network isolation = separate and control communication [OK]

Hint: Network isolation means controlling service communication [OK]

Common Mistakes:

• Confusing network isolation with image size optimization
• Thinking it speeds up container startup
• Assuming it updates containers automatically

2. Which Docker command creates a custom network for isolating services?

easy

A. docker image build my-network

B. docker container run my-network

C. docker network create my-network

D. docker service start my-network

Solution

1. Step 1: Identify command to create network

   The command to create a Docker network is docker network create followed by the network name.

2. Step 2: Match correct syntax

   docker network create my-network uses the correct syntax: docker network create my-network.

3. Final Answer:

   docker network create my-network -> Option C

4. Quick Check:

   Creating network = docker network create [OK]

Hint: Use 'docker network create' to make custom networks [OK]

Common Mistakes:

• Using 'docker container run' to create networks
• Confusing image build with network creation
• Trying to start a service to create a network

3. Given two containers attached to different custom networks, what happens if one tries to ping the other by container name?

medium

A. Ping succeeds because Docker allows cross-network communication by default

B. Ping fails because containers on different networks cannot resolve each other's names

C. Ping succeeds only if both containers share the same image

D. Ping fails unless both containers are on the default bridge network

Solution

1. Step 1: Understand Docker network isolation

   Containers on different custom networks cannot communicate or resolve each other's names by default.

2. Step 2: Analyze ping behavior

   Since they are on separate networks, ping by container name will fail due to no DNS resolution across networks.

3. Final Answer:

   Ping fails because containers on different networks cannot resolve each other's names -> Option B

4. Quick Check:

   Different networks = no name resolution [OK]

Hint: Containers on different networks can't ping by name [OK]

Common Mistakes:

• Assuming default bridge allows all communication
• Thinking image similarity affects network reachability
• Believing Docker allows cross-network DNS by default

4. You created two services on the same custom network but they cannot communicate. What is the most likely mistake?

medium

A. The services have the same container name

B. The network was created with the wrong driver

C. The services are not attached to the same network

D. The containers are running on different Docker hosts

Solution

1. Step 1: Check network attachment

   If services are on the same network, they should communicate unless other factors block it.

2. Step 2: Consider Docker host location

   If containers run on different Docker hosts without overlay network, they cannot communicate even on the same network name.

3. Final Answer:

   The containers are running on different Docker hosts -> Option D

4. Quick Check:

   Different hosts without overlay = no communication [OK]

Hint: Check if containers run on same host or overlay network [OK]

Common Mistakes:

• Assuming same network name means same network across hosts
• Ignoring network driver type
• Confusing container names with network connectivity

5. You want two services to communicate but keep them isolated from all other containers. Which is the best approach?

hard

A. Create a custom network and attach only these two services to it

B. Use the default bridge network for both services

C. Attach both services to multiple networks including default

D. Run both services on the host network

Solution

1. Step 1: Understand isolation needs

   To isolate two services from others, they must be on a private network only they share.

2. Step 2: Choose network setup

   Creating a custom network and attaching only these two services ensures isolation and communication.

3. Step 3: Evaluate other options

   Default bridge includes all containers, multiple networks reduce isolation, host network removes isolation.

4. Final Answer:

   Create a custom network and attach only these two services to it -> Option A

5. Quick Check:

   Custom network with only two services = isolation + communication [OK]

Hint: Use custom network with only needed services attached [OK]

Common Mistakes:

• Using default network which includes all containers
• Attaching services to multiple networks losing isolation
• Using host network which disables isolation