🔗 Building php docker images in a better way with wolfi-os

Currently, the de-facto standard to dockerizing PHP applications is to use the Docker PHP official image. This is maintained by Docker itself and community members and has compiled PHP with no extensions. To install extensions, we have to do this in our Dockerfile:

FROM php:8.2-cli
RUN docker-php-ext-install pdo pdo_mysql curl

The helper script docker-php-ext-install does unpack the PHP source code and installs the given extensions. For some extensions like gd, we need also libraries installed like libpng and so on. So we have to install manually before the library with dev dependencies and remove it afterwards (we need the development headers to compile the extension).

Luckily, this problem has been solved already by the Community with the docker-php-extension-installer. So instead we install manually apt or apk packages, we just use this script, and it takes care of that. The usage looks like this:

FROM php:8.2-cli
ADD --chmod=0755 https://github.com/mlocati/docker-php-extension-installer/releases/latest/download/install-php-extensions /usr/local/bin/
RUN install-php-extensions pdo pdo_mysql gd curl

This takes 20s on my machine (I have a high-end gaming machine, not comparable to real CI) and produces a Docker image which is 557MB.

❯ docker images
REPOSITORY          TAG       IMAGE ID       CREATED         SIZE
php                 latest    683c45c057f0   38 seconds ago  557MB

Huh, that’s much. Usually, the solution which many people are considering is then to use the Alpine variant. The Alpine variant is normally much smaller, but uses a different libc so musl. There already some known PHP issues to Alpine variant images, also there are known performance issues with allocation, see FrankenPHP issue.

But anyway, let’s do the same again on alpine to just compare the size. So we added additionally an -alpine flag to the base image.

FROM php:8.2-cli-alpine
ADD --chmod=0755 https://github.com/mlocati/docker-php-extension-installer/releases/latest/download/install-php-extensions /usr/local/bin/
RUN install-php-extensions pdo pdo_mysql gd curl

and the image is after compiling

❯ docker images
REPOSITORY          TAG       IMAGE ID       CREATED         SIZE
php                 latest    8651ba41dbd1   37 seconds ago  114MB

from 557MB to just 114MB, that’s really good. The next pain point of the official docker image is building a multi arch image.