Docker deployment in Laravel - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when running Laravel inside Docker with this Dockerfile?

Consider this Dockerfile for a Laravel app. What will be the result when you build and run the container?

FROM php:8.1-fpm
WORKDIR /var/www/html
COPY . .
RUN docker-php-ext-install pdo pdo_mysql
CMD ["php-fpm"]

Laravel

FROM php:8.1-fpm
WORKDIR /var/www/html
COPY . .
RUN docker-php-ext-install pdo pdo_mysql
CMD ["php-fpm"]

A The container runs PHP-FPM serving the Laravel app, but no web server is included so no HTTP requests are handled.

B The container runs a full Apache server serving the Laravel app out of the box.

C The container fails to build because pdo_mysql extension is not available for PHP 8.1.

D The container runs but Laravel will not connect to the database because no database service is included.

💡 Hint

Think about what PHP-FPM does and what is missing to serve HTTP requests.

This Dockerfile uses the official PHP-FPM image which runs PHP FastCGI Process Manager. It does not include a web server like Apache or Nginx. So while PHP runs, HTTP requests won't be served unless a web server is added.

📝 Syntax

intermediate

Which docker-compose.yml snippet correctly defines a Laravel app with MySQL service?

You want to run Laravel with a MySQL database using Docker Compose. Which snippet is correct?

Laravel

version: '3.8'
services:
  app:
    build: .
    ports:
      - "8000:80"
    depends_on:
      - db
  db:
    image: mysql:8
    environment:
      MYSQL_ROOT_PASSWORD: secret
      MYSQL_DATABASE: laravel
      MYSQL_USER: user
      MYSQL_PASSWORD: secret

A The app service should expose port 3306 for MySQL, not 8000.

B The snippet is missing volumes for persistent MySQL data, so data will be lost on restart.

C The snippet is correct and will start Laravel app on port 8000 with MySQL database.

D The environment variables for MySQL are incorrect; MYSQL_USER is not valid.

💡 Hint

Check if the services and environment variables match Laravel and MySQL requirements.

This docker-compose.yml correctly defines an app service built from the current directory and a MySQL 8 service with proper environment variables. Port 8000 is mapped for the app HTTP traffic. Volumes are recommended but not required.

🔧 Debug

advanced

Why does Laravel fail to connect to MySQL in this Docker setup?

Given this docker-compose.yml snippet:

services:
  app:
    build: .
    environment:
      DB_HOST: localhost
      DB_DATABASE: laravel
      DB_USERNAME: user
      DB_PASSWORD: secret
  db:
    image: mysql:8
    environment:
      MYSQL_ROOT_PASSWORD: secret
      MYSQL_DATABASE: laravel
      MYSQL_USER: user
      MYSQL_PASSWORD: secret

Laravel inside the app container cannot connect to MySQL. Why?

Laravel

services:
  app:
    build: .
    environment:
      DB_HOST: localhost
      DB_DATABASE: laravel
      DB_USERNAME: user
      DB_PASSWORD: secret
  db:
    image: mysql:8
    environment:
      MYSQL_ROOT_PASSWORD: secret
      MYSQL_DATABASE: laravel
      MYSQL_USER: user
      MYSQL_PASSWORD: secret

A DB_HOST should be 'db' not 'localhost' because containers have separate networks.

B The MySQL image version 8 is incompatible with Laravel's database driver.

C The environment variables must be set in a .env file, not in docker-compose.yml.

D The app container needs to expose port 3306 to connect to MySQL.

💡 Hint

Think about how Docker containers communicate by service name, not localhost.

Inside Docker Compose, containers communicate using service names as hostnames. 'localhost' refers to the container itself, so Laravel cannot reach the MySQL container using 'localhost'. Using 'db' as DB_HOST fixes this.

❓ lifecycle

advanced

What happens if you run 'docker-compose down' in a Laravel Docker setup with volumes?

You have a Laravel app and MySQL running with Docker Compose. The MySQL service uses a named volume for data. What happens when you run 'docker-compose down'?

Laravel

version: '3.8'
services:
  app:
    build: .
  db:
    image: mysql:8
    volumes:
      - mysql_data:/var/lib/mysql
volumes:
  mysql_data:

A The command fails because volumes cannot be used with 'docker-compose down'.

B The containers and the MySQL data volume are deleted, losing all database data.

C Only the app container is removed; the db container and volume remain running.

D The containers stop and are removed, but the MySQL data volume remains intact.

💡 Hint

Consider the difference between 'docker-compose down' and 'docker-compose down -v'.

'docker-compose down' stops and removes containers and networks but preserves named volumes. To remove volumes, you must add the '-v' flag.

🧠 Conceptual

expert

Which is the best way to optimize Laravel Docker image size for production?

You want to deploy a Laravel app with Docker in production. Which approach best reduces the final image size while keeping functionality?

A Use a single Dockerfile with all build tools and runtime in one image to avoid complexity.

B Use a multi-stage Dockerfile: build assets and dependencies in one stage, then copy only needed files to a smaller PHP runtime image.

C Use the official php:8.1-fpm image and install all composer dependencies and node modules inside it directly.

D Use Alpine Linux base image and install all Laravel dependencies manually to minimize size.

💡 Hint

Think about separating build environment from runtime environment.

Multi-stage builds allow compiling and installing dependencies in a build stage, then copying only the necessary runtime files to a smaller base image. This reduces image size and attack surface.

Practice

1. What is the main purpose of using Docker for deploying a Laravel application?

easy

A. To package the Laravel app with all its dependencies for consistent environments

B. To write Laravel code faster using special Docker commands

C. To replace Laravel's routing system with Docker's networking

D. To automatically generate Laravel migrations

Solution

1. Step 1: Understand Docker's role in deployment

   Docker packages the app and its environment so it runs the same everywhere.

2. Step 2: Relate this to Laravel deployment

   Laravel apps need PHP, web server, database, and dependencies; Docker bundles these.

3. Final Answer:

   To package the Laravel app with all its dependencies for consistent environments -> Option A

4. Quick Check:

   Docker ensures consistent app environment = C [OK]

Hint: Docker bundles app and tools for same setup everywhere [OK]

Common Mistakes:

• Thinking Docker speeds up coding
• Confusing Docker with Laravel features
• Believing Docker replaces Laravel's internal functions

2. Which file is typically used to define the environment and instructions to build a Docker image for a Laravel app?

easy

A. .env

B. docker-compose.yml

C. Dockerfile

D. composer.json

Solution

1. Step 1: Identify Dockerfile's purpose

   Dockerfile contains commands to build the Docker image step-by-step.

2. Step 2: Differentiate from other files

   docker-compose.yml runs containers; .env holds app configs; composer.json manages PHP packages.

3. Final Answer:

   Dockerfile -> Option C

4. Quick Check:

   Dockerfile builds image = A [OK]

Hint: Dockerfile builds image; compose runs containers [OK]

Common Mistakes:

• Confusing docker-compose.yml with Dockerfile
• Thinking .env defines Docker build steps
• Mixing composer.json with Docker configs

3. Given this docker-compose.yml snippet for Laravel:

services:
  app:
    build: .
    ports:
      - "8000:80"
    volumes:
      - .:/var/www/html
  db:
    image: mysql:8
    environment:
      MYSQL_ROOT_PASSWORD: secret

What happens when you run docker-compose up?

medium

A. It builds the app image, runs app on port 8000, and starts MySQL with root password

B. It only runs MySQL container without the app

C. It builds app image but fails to start MySQL due to missing password

D. It runs app on port 80 without MySQL

Solution

1. Step 1: Analyze docker-compose services

   App service builds from current folder, maps port 8000 to container's 80, mounts code volume. DB uses MySQL image with root password set.

2. Step 2: Understand docker-compose up behavior

   It builds and starts all defined services, so both app and db run with given configs.

3. Final Answer:

   It builds the app image, runs app on port 8000, and starts MySQL with root password -> Option A

4. Quick Check:

   Compose runs all services with configs = B [OK]

Hint: docker-compose up runs all services with given configs [OK]

Common Mistakes:

• Assuming only one service runs
• Missing environment variable for MySQL password
• Confusing port mapping direction

4. You wrote this Dockerfile for Laravel but get an error when building:

FROM php:8.1-fpm
RUN apt-get update && apt-get install -y git zip unzip
COPY . /var/www/html
RUN composer install

What is the likely cause of the build failure?

medium

A. apt-get update should be run after composer install

B. COPY command syntax is incorrect

C. PHP version 8.1-fpm is not supported by Laravel

D. Missing installation of Composer before running composer install

Solution

1. Step 1: Check Dockerfile commands order

   Composer is a separate tool and must be installed before running composer install.

2. Step 2: Identify missing Composer installation

   Dockerfile does not install Composer, so the command fails.

3. Final Answer:

   Missing installation of Composer before running composer install -> Option D

4. Quick Check:

   Composer must be installed before use = D [OK]

Hint: Install Composer before running composer commands [OK]

Common Mistakes:

• Assuming PHP image includes Composer by default
• Thinking COPY syntax causes build error
• Believing PHP 8.1-fpm is incompatible with Laravel

5. You want to deploy a Laravel app with Docker using docker-compose. You need PHP, MySQL, and Redis services. Which docker-compose.yml snippet correctly sets up these services with proper ports and environment variables?

hard

A. services:
app:
image: laravel/php
ports:
- "80:80"
db:
image: mysql
environment:
MYSQL_PASSWORD: secret
cache:
image: redis
ports:
- "6379:6379"

B. services:
app:
build: .
ports:
- "8080:80"
volumes:
- .:/var/www/html
db:
image: mysql:8
environment:
MYSQL_ROOT_PASSWORD: secret
cache:
image: redis:latest
ports:
- "6379:6379"

C. services:
app:
build: .
ports:
- "80:8080"
db:
image: mysql:5.7
environment:
MYSQL_ROOT_PASSWORD: root
cache:
image: redis
ports:
- "6379:6379"

D. services:
app:
build: .
ports:
- "8000:8000"
db:
image: mysql:8
environment:
MYSQL_ROOT_PASSWORD: secret
cache:
image: redis:latest

Solution

1. Step 1: Check app service configuration

   services: app: build: . ports: - "8080:80" volumes: - .:/var/www/html db: image: mysql:8 environment: MYSQL_ROOT_PASSWORD: secret cache: image: redis:latest ports: - "6379:6379" builds app from current folder, maps port 8080 to container port 80, and mounts code volume correctly.

2. Step 2: Verify db and cache services

   MySQL uses image mysql:8 with root password set; Redis uses latest image and exposes default port 6379.

3. Step 3: Compare other options for correctness

   services: app: image: laravel/php ports: - "80:80" db: image: mysql environment: MYSQL_PASSWORD: secret cache: image: redis ports: - "6379:6379". This option misses the volume mount for app code and uses wrong environment variable for MySQL (MYSQL_PASSWORD instead of MYSQL_ROOT_PASSWORD); the option with app ports "80:8080" has wrong port mapping; the option without ports for Redis misses exposing the Redis port.

4. Final Answer:

   services: app: build: . ports: - "8080:80" volumes: - .:/var/www/html db: image: mysql:8 environment: MYSQL_ROOT_PASSWORD: secret cache: image: redis:latest ports: - "6379:6379" -> Option B

5. Quick Check:

   Correct service setup with ports and env = A [OK]

Hint: Check ports and env vars carefully for all services [OK]

Common Mistakes:

• Swapping port mappings (host:container)
• Using wrong environment variable names
• Omitting volume mounts for app code
• Not exposing Redis port