Compose watch for development in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to start services in detached mode using Docker Compose.

Docker

docker-compose up -[1]

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

Ar

Bf

Cd

Ds

Attempts:

3 left

💡 Hint

Common Mistakes

Using -f which is for specifying a file

Using -r which is not a valid flag here

The -d flag runs Docker Compose services in detached mode, allowing the terminal to be free.

2fill in blank

medium

Complete the command to rebuild services before starting them.

Docker

docker-compose up --[1]

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

Aforce-recreate

Bbuild

Crebuild

Drestart

Attempts:

3 left

💡 Hint

Common Mistakes

Using --force-recreate which recreates containers but does not build images

Using --rebuild which is not a valid option

The --build option forces Docker Compose to build images before starting containers.

3fill in blank

hard

Fix the error in the command to watch file changes and restart services automatically.

Docker

docker-compose up -[1] --watch

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

Adetach

Bdetached

Cdetach-mode

Dd

Attempts:

3 left

💡 Hint

Common Mistakes

Using --watch which is not supported

Using incorrect long flags like --detached

The correct short flag for detached mode is -d. The long form is --detach, but --watch is not a valid Docker Compose flag.

4fill in blank

hard

Fill both blanks to create a service that watches for file changes and restarts automatically using a tool.

Docker

version: '3.8'\nservices:\n  app:\n    build: .\n    command: [1] --watch [2] app.js\n    volumes:\n      - .:/app\n    ports:\n      - '3000:3000'\n

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

Anodemon

Bnode

C--exec

D.

Attempts:

3 left

💡 Hint

Common Mistakes

Using node instead of nodemon

Using --exec which runs a command but does not watch files

nodemon is a tool that watches for file changes and restarts the Node.js app automatically. The --watch flag tells nodemon which files or folders to watch.

5fill in blank

hard

Fill all three blanks to define a Docker Compose service that uses a volume, sets environment variables, and runs a watch command.

Docker

version: '3.8'\nservices:\n  web:\n    build: .\n    volumes:\n      - [1]:/usr/src/app\n    environment:\n      - NODE_ENV=[2]\n    command: [3] --watch src\n    ports:\n      - '8080:8080'\n

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

A./app

Bdevelopment

Cnodemon

D./src

Attempts:

3 left

💡 Hint

Common Mistakes

Using ./src as volume instead of ./app

Setting NODE_ENV to production

Using node instead of nodemon

The volume maps the local ./app folder to the container path. The environment variable NODE_ENV is set to development for dev mode. The command uses nodemon to watch the src folder for changes.

Practice

1. What is the main purpose of using docker-compose watch during development?

easy

A. To deploy the app to production servers

B. To build the Docker image only once

C. To automatically reload the application when code changes

D. To monitor container resource usage

Solution

1. Step 1: Understand the role of watch in development

   Watching means tracking file changes to trigger actions automatically.

2. Step 2: Connect watch with docker-compose usage

   Compose watch reloads the app inside the container when source code changes on the host.

3. Final Answer:

   To automatically reload the application when code changes -> Option C

4. Quick Check:

   Compose watch = auto reload on code change [OK]

Hint: Watch means auto reload on code change [OK]

Common Mistakes:

• Confusing watch with building images
• Thinking watch deploys to production
• Assuming watch monitors resource usage

2. Which of the following docker-compose.yml volume configurations correctly syncs your local source code to the container for live reload?

easy

A. volumes:\n - ./app:/app

B. volumes:\n - /app:/app

C. volumes:\n - ./app

D. volumes:\n - /app

Solution

1. Step 1: Understand volume syntax in docker-compose

   Volumes map host paths to container paths using host_path:container_path.

2. Step 2: Identify correct host to container mapping

   ./app:/app maps local folder app to container's /app for syncing code.

3. Final Answer:

   volumes:\n - ./app:/app -> Option A

4. Quick Check:

   Host path before colon, container path after [OK]

Hint: Volume syntax: host_path:container_path [OK]

Common Mistakes:

• Reversing host and container paths
• Omitting container path
• Using absolute container path as host path

3. Given this docker-compose.yml snippet and a Node.js app using nodemon:

services:
  web:
    volumes:
      - ./src:/usr/src/app
    command: nodemon index.js

What happens when you edit a file inside ./src on your host machine?

medium

A. Nothing happens until you rebuild the image

B. The container deletes the edited file

C. The container crashes due to volume conflict

D. The container restarts the Node.js app automatically

Solution

1. Step 1: Understand volume syncing

   The volume syncs ./src on host to /usr/src/app in container, so changes reflect inside container.

2. Step 2: Understand nodemon behavior

   nodemon watches files and restarts the app when files change.

3. Final Answer:

   The container restarts the Node.js app automatically -> Option D

4. Quick Check:

   Volume sync + nodemon = auto restart on code change [OK]

Hint: Nodemon restarts app on synced file changes [OK]

Common Mistakes:

• Thinking image rebuild is needed for code changes
• Assuming container crashes on volume use
• Believing files are deleted on sync

4. You set up docker-compose with volumes and watchmedo to reload a Python app, but changes don't trigger reload. What is the most likely cause?

medium

A. The volume path is incorrect or missing

B. The Dockerfile lacks a CMD instruction

C. The container has no network access

D. The image was not built with --no-cache

Solution

1. Step 1: Check volume configuration

   If volumes don't map host code to container, changes won't appear inside container.

2. Step 2: Understand watchmedo needs code inside container

   Without synced code, watchmedo cannot detect changes to reload app.

3. Final Answer:

   The volume path is incorrect or missing -> Option A

4. Quick Check:

   Missing volume = no code sync = no reload [OK]

Hint: Check volumes if reload doesn't work [OK]

Common Mistakes:

• Blaming CMD instead of volumes
• Assuming network affects file watching
• Thinking image cache affects reload

5. You want to set up a development environment with docker-compose that automatically reloads a React app on code changes. Which combination below is the best practice?

hard

A. Build image with source code baked in, run npm run build once

B. Use volumes to sync source code, run npm start with react-scripts watch mode inside container

C. Use volumes but disable hot reload to avoid conflicts

D. Run npm start on host and use container only for database

Solution

1. Step 1: Sync source code with volumes

   Volumes keep container code updated with host edits for live reload.

2. Step 2: Use React's built-in watch mode

   npm start with react-scripts runs dev server that reloads on changes.

3. Final Answer:

   Use volumes to sync source code, run npm start with react-scripts watch mode inside container -> Option B

4. Quick Check:

   Volumes + watch mode = best dev reload setup [OK]

Hint: Sync code + run dev server with watch mode [OK]

Common Mistakes:

• Baking code into image prevents live reload
• Disabling hot reload loses dev speed
• Running app only on host misses container benefits