Install PHP Dependencies in Docker

Why dependencies matter

• Features. Libraries add functions that you do not have to write.
• Security and updates. Updating dependencies brings security fixes.
• Compatibility. Managing versions keeps your app running.
• Reuse. Many libraries work in many projects.

PHP package tools

• Composer. The standard dependency manager for PHP.
• PEAR. An older packaging system for PHP extensions.
• PHP-CLI. The command-line PHP, used to run Composer and scripts.

What you need

• Docker, installed from the official website.
• Composer is added inside the container in this guide, so you do not need it on the host.

Step 1: Create a project folder

mkdir my-php-app
cd my-php-app

Step 2: Create a Dockerfile

Create a file named Dockerfile:

# Use an official PHP image
FROM php:8.2-cli

# Install system tools and PHP extensions
RUN apt-get update && apt-get install -y git unzip libzip-dev \
    && docker-php-ext-install zip pdo_mysql \
    && rm -rf /var/lib/apt/lists/*

# Install Composer from its official image
COPY --from=composer:2 /usr/bin/composer /usr/bin/composer

# Set the working directory
WORKDIR /usr/src/myapp

# Copy the dependency files first, to use the Docker cache
COPY composer.json composer.lock* ./

# Install the PHP dependencies
RUN composer install --no-dev --no-interaction --prefer-dist

# Copy the rest of the app
COPY . .

CMD ["php", "./index.php"]

Step 3: Add composer.json

Create composer.json with the packages you need, for example:

{
    "require": {
        "monolog/monolog": "^3.0"
    }
}

Or create it by running Composer in a temporary container:

docker run --rm -v "$PWD":/app composer:2 require monolog/monolog

Step 4: Add a test script

Create index.php:

<?php
require __DIR__ . '/vendor/autoload.php';

use Monolog\Logger;
use Monolog\Handler\StreamHandler;

$log = new Logger('app');
$log->pushHandler(new StreamHandler('php://stdout'));
$log->info('Hello from Docker');

Step 5: Build the image

docker build -t my-php-app .

Step 6: Run the container

docker run --rm my-php-app

You should see the log line.

Tips

• Copy composer.json before the rest of the code, so Docker re-uses the cached layer when only your code changes.
• Use --no-dev in production images.
• Use a .dockerignore file with vendor and .git.
• Add more extensions with docker-php-ext-install or with the mlocati/php-extension-installer helper.

Quick recap

• Put Composer in the image with COPY --from=composer:2.
• Run composer install in the Dockerfile.
• Build with docker build and run with docker run.