Container DNS and service discovery in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run a container with a custom network for DNS-based service discovery.

Docker

docker network create my_network

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

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

Abridge

Bnone

Chost

Dmy_network

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'bridge' network which does not enable container name DNS resolution.

Using 'host' network which bypasses Docker networking.

Forgetting to create the custom network before running the container.

Using --network my_network connects the container to the custom network my_network, enabling DNS-based service discovery within that network.

2fill in blank

medium

Complete the command to run a second container that can reach the first container by its name using Docker DNS.

Docker

docker run --rm -it --network my_network busybox ping [1]

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

Alocalhost

B127.0.0.1

Cwebapp

Dgoogle.com

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'localhost' which refers to the current container.

Using an external domain like 'google.com' which is unrelated to Docker DNS.

Using the container name webapp allows the second container to resolve and ping the first container via Docker's internal DNS on the same network.

3fill in blank

hard

Fix the error in the Docker Compose service definition to enable service discovery by service name.

Docker

version: '3'
services:
  app:
    image: myapp
    networks:
      - [1]
networks:
  mynet:
    driver: bridge

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

Amynet

Bbridge

Cdefault

Dhost

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'bridge' which is a driver, not the network name.

Using 'host' which disables Docker network isolation.

The service must be connected to the defined network mynet to enable DNS-based service discovery within that network.

4fill in blank

hard

Fill both blanks to create a Docker Compose file that defines two services communicating via service names on a custom network.

Docker

version: '3'
services:
  frontend:
    image: frontend_image
    networks:
      - [1]
  backend:
    image: backend_image
    networks:
      - [2]
networks:
  appnet:
    driver: bridge

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

Aappnet

Bbridge

Cdefault

Dhost

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning different networks to services prevents DNS-based communication.

Using 'default' network name which is not defined explicitly.

Both services must be connected to the same custom network appnet to communicate using service names.

5fill in blank

hard

Fill all three blanks to create a Docker Compose snippet that uses environment variables to configure the backend service URL for the frontend service.

Docker

version: '3'
services:
  frontend:
    image: frontend_image
    environment:
      - BACKEND_URL=http://[1]:[2]
    networks:
      - [3]
  backend:
    image: backend_image
    networks:
      - appnet
networks:
  appnet:
    driver: bridge

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

Abackend

B8080

Cappnet

Dfrontend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'frontend' as hostname instead of 'backend'.

Using wrong port number or network name.

The frontend uses the service name backend and port 8080 to reach the backend. Both services are on the appnet network for DNS resolution.