Incomplete Dockerfile

Difficulty: Easy — 3 missing pieces

What This Challenge Is

A Dockerfile for DALT.PHP has been started but is missing three critical parts. The image cannot be built until all three are added.

Run the challenge to load the incomplete Dockerfile into your project root:

php artisan challenge:start docker-incomplete-dockerfile

Then open Dockerfile in your editor and complete it.

The Three Missing Parts

1. Working directory

PHP-FPM expects to serve files from /var/www/html. Every COPY and RUN instruction after this point will execute from that path. Without it, your files land at / (the root) and paths break.

The instruction is WORKDIR. Set it to /var/www/html.

2. PHP extensions

DALT.PHP uses PDO to connect to databases. The pdo extension provides the base PDO class. The pdo_pgsql extension provides the PostgreSQL driver. Neither is installed in the base php:8.2-fpm-alpine image.

The helper command for installing PHP extensions inside Docker is docker-php-ext-install. You can install multiple extensions in one RUN command by listing them space-separated.

The RUN instruction must come before the COPY instructions — this keeps the slow extension compilation in a cached layer.

3. CMD to start PHP-FPM

When the container starts, it needs to know what process to run. PHP-FPM is started with the php-fpm command. Use the array form of CMD so the process runs as PID 1 and receives signals correctly.

Files Involved

• Dockerfile — the only file you need to edit

Verify Your Solution

php artisan challenge:verify

The verifier checks:

• WORKDIR /var/www/html is present
• docker-php-ext-install is called
• pdo_pgsql extension is installed
• CMD ["php-fpm"] is present
• No # TODO comments remain

Testing the Build

After verifying, try actually building the image:

docker build -t dalt-php .

A successful build ends with:

Successfully built <hash>
Successfully tagged dalt-php:latest

If it fails, read the error — Docker tells you exactly which layer failed and why.

Hints

• WORKDIR takes a single path argument: WORKDIR /var/www/html
• docker-php-ext-install pdo pdo_pgsql — both on the same line saves one layer
• CMD ["php-fpm"] — square brackets, quoted string, no flags needed

Why These Three Things

WORKDIR: Without it, COPY composer.json ./ copies to /composer.json, not /var/www/html/composer.json. Nginx points at /var/www/html — your files are in the wrong place.

Extensions: Without pdo_pgsql, the database connection throws: could not find driver. Without pdo, nothing database-related works at all.

CMD: Without CMD, the container starts but has no process to run. It exits immediately. A container stops when its main process stops.

Next Challenge

After completing this, move on to docker-broken-nginx to fix the Nginx configuration that routes HTTP requests to PHP-FPM.