S6 nginx/php-fpm container

usage

This is a simple container with nginx and php-fpm based on alpine linux. To install all the dependencies and build the container run:

make up

What is this about

We often have the case that we need to deploy our PHP application to $server, but since PHP does not come with its own webserver we always run a second container which passes the requests to our PHP process. We looked into many options and decided against them for different reasons.

• Kubernetes: Overkill for a PHP-Application
• Docker Compose: Not recommended in production, not well documented
• FrankenPHP: Not stable enough (at the time), written in go, compiles PHP
• SupervisorD: Not recommended for running as PID 1 in a dockerized environment
• SystemD: Not available for alpine (package requires gclib)
• s6-overlay: Works like a charm in ubuntu (glibc) and alpine (musl) and is made for running as PID 1 in container

What are the components

We installed just an index file in the app directory to showcase a running php application.

• Alpine
• s6-overlay
• nginx
• php-fpm

We use preconfigured user www-data and install the app in var/www/html.

s6-overlay

• starts PID 1 with ENTRYPOINT ["/init"]
• starts all services and scripts that are defined in /etc/s6-overlay/s6-rc.d/user/contents.d

Recipes

Use cases and how they can be solved using s6

Feature Flags

Sometimes you need to enable or disable services.

s6-rc wasn't made for dynamic service sets; it was made for reliability and predictability of the machine state, which runtime changes are bad for - and you're going against its design by attempting to conditionally start services.

The way to achieve what you want is by making sure that only the services you want to activate are in s6-rc's user bundle, which contains everything that will be started. For that purpose, you have the S6_STAGE2_HOOK environment variable: in it, put the path to a script, and that script will be run before s6-rc analyzes its service set. That script should be the one to read your environment variables, and adjust the files of /etc/s6-overlay/s6-rc.d/user/contents accordingly.

# docker-compose.yml
services:
  app:
    environment:
      S6_STAGE2_HOOK: /etc/s6-hook/feature-toggle
      FEATURE_MIGRATIONS_ENABLED: "false"

/etc/s6-hook/feature-toggle

#!/command/with-contenv sh

# Read environment variable and default to "false" if not set
INIT_MIGRATIONS="${FEATURE_MIGRATIONS_ENABLED:-false}"

# Define a space-separated list of feature toggles (since arrays are not supported in sh)
# the feature name is the upper SNAKE_CASE version of the feature directory name in lower kebab-case
features="INIT_MIGRATIONS"

# Iterate through each feature toggle
for feature in $features; do
    # Get the value of the environment variable, default to "false" if not set
    is_enabled=$(eval echo \${$feature:-false})

    # Convert the feature name to lowercase and replace underscores with hyphens
    feature_file=$(echo "$feature" | tr 'A-Z' 'a-z' | tr '_' '-')

    # Check if the feature is enabled
    if [ "$is_enabled" = "true" ]; then
        touch "/etc/s6-overlay/s6-rc.d/user/contents.d/$feature_file"
    else
        rm -f "/etc/s6-overlay/s6-rc.d/user/contents.d/$feature_file"
    fi
done

exit 0

Doctrine Migrations

/etc/s6-overlay/s6-rc.d
├── init-migrations
│   ├── dependencies.d
│   │    └── svc-php-fpm
│   ├── type
│   └── up
└── scripts
        └── init-migrations

#!/command/with-contenv sh
s6-setuidgid www-data

php /var/www/html/bin/console doctrine:migrations:migrate --env=`printcontenv APP_ENV` --no-interaction
php /var/www/html/bin/console doctrine:migrations:status --env=`printcontenv APP_ENV`

CronJobs with Symfony Scheduler Component

/etc/s6-overlay/s6-rc.d
├── svc-scheduler
│   ├── dependencies.d
│   │    └── svc-php-fpm
│   ├── type
│   └── up
└── scripts
        └── svc-scheduler

#!/command/with-contenv sh
s6-setuidgid www-data

php /var/www/html/bin/console messenger:consume scheduler_default \
  --time-limit=300 \
  --limit=10 \
  --env=`printcontenv APP_ENV` --quiet

check requirements in dev

/etc/s6-overlay/s6-rc.d
├── init-dependencies
│   ├── dependencies.d
│   │    ├── base
│   │    └── svc-php-fpm
│   ├── type
│   └── up
└── scripts
        └── init-dependencies

#!/command/with-contenv sh

# Check if the composer binary exists
if command -v composer >/dev/null 2>&1; then
    # Composer is installed, run composer install
    echo "init-dependencies: info: Composer found. Checking dependencies."
    composer -d /var/www/html check-platform-reqs
    exit 0
fi
echo "init-dependencies: info: Composer not found. Please install Composer before running this script."
exit 0