Joomla 5 in Docker.
Headless install, production ready.

Architecture at a glance

• Joomla (Apache and PHP) serves plain HTTP on port 80. TLS is terminated upstream by a reverse proxy (Traefik on the RemarkableCloud App Platform), so there is no in-container certificate to manage.
• MariaDB is a separate database container and holds all site content and configuration.
• A data volume at /var/www/html holds Joomla itself, configuration.php, extensions, templates, and uploaded media.

Docker Compose walkthrough

The standalone stack (Joomla and MariaDB) is defined in the image’s docker-compose.yml:

name: joomla
services:
  db:
    image: mariadb:11
    restart: unless-stopped
    environment:
      MARIADB_DATABASE: joomla
      MARIADB_USER: joomla
      MARIADB_PASSWORD: ${DB_PASSWORD:-change-me-db}
      MARIADB_ROOT_PASSWORD: ${DB_ROOT_PASSWORD:-change-me-root}
    volumes: [db-data:/var/lib/mysql]
    healthcheck:
      test: ["CMD", "healthcheck.sh", "--connect", "--innodb_initialized"]
      interval: 10s
      timeout: 5s
      retries: 12
  joomla:
    image: ${JOOMLA_IMAGE:-ghcr.io/remarkablecloud/joomla:5-r1}
    restart: unless-stopped
    depends_on:
      db:
        condition: service_healthy
    ports: ["${HTTP_PORT:-8087}:80"]
    environment:
      JOOMLA_DB_TYPE: mysqli
      JOOMLA_DB_HOST: db
      JOOMLA_DB_NAME: joomla
      JOOMLA_DB_USER: joomla
      JOOMLA_DB_PASSWORD: ${DB_PASSWORD:-change-me-db}
      JOOMLA_SITE_NAME: ${JOOMLA_SITE_NAME:-Joomla}
      JOOMLA_ADMIN_USER: ${JOOMLA_ADMIN_USER:-Administrator}
      JOOMLA_ADMIN_USERNAME: ${JOOMLA_ADMIN_USERNAME:-admin}
      JOOMLA_ADMIN_PASSWORD: ${JOOMLA_ADMIN_PASSWORD:-}
      JOOMLA_ADMIN_EMAIL: ${JOOMLA_ADMIN_EMAIL:-admin@example.com}
    volumes:
      - joomla-data:/var/www/html
volumes:
  db-data:
  joomla-data:

Step by step:

1. The app waits for the database. depends_on with condition: service_healthy avoids a first-boot race against MariaDB.
2. Install is headless. The JOOMLA_DB_* and JOOMLA_ADMIN_* variables let Joomla install on first start without the web wizard.
3. The admin password is generated if blank. Leave JOOMLA_ADMIN_PASSWORD empty and the image creates a strong one on first install and logs it once.
4. Only the web port is exposed. ${HTTP_PORT:-8087}:80 is for local use; in production the proxy connects to port 80 on the internal network.
5. State lives in volumes. joomla-data (/var/www/html) and db-data persist across restarts and upgrades.

To start it locally:

DB_PASSWORD=$(openssl rand -hex 16) docker compose up -d

Then browse to http://localhost:8087 and read the generated admin password from docker compose logs joomla. Change it and the admin email after first login.

Environment variable reference

These are wired automatically by the App Platform backend from the managed MariaDB; they are listed here for standalone and self-hosted runs.

Variable	Required	Value / default	Purpose
JOOMLA_DB_TYPE	yes	mysqli	Database driver.
JOOMLA_DB_HOST	yes	<db_host>	MariaDB host.
JOOMLA_DB_NAME	yes	<db_name>	Database name.
JOOMLA_DB_USER	yes	<db_user>	Database user.
JOOMLA_DB_PASSWORD	yes	<db_password>	Database password.
JOOMLA_SITE_NAME	no	Joomla	Site title.
JOOMLA_ADMIN_USER	yes	Administrator	Admin display name.
JOOMLA_ADMIN_USERNAME	yes	admin	Admin login.
JOOMLA_ADMIN_PASSWORD	no	(generated)	Admin password. Leave empty to auto-generate on first install; printed once to the log.
JOOMLA_ADMIN_EMAIL	yes	admin@example.com	Admin email.

Only the first install reads these; once configuration.php exists they are ignored, and account changes happen inside Joomla.

Hardening notes

• No baked credentials. The admin password is generated at first install or supplied by you, never stored in an image layer.
• Digest-pinned base. Each build is auditable and reproducible.
• Healthcheck gates traffic. / must return success before the platform routes requests.
• Keep MariaDB private. Do not publish its port to the host or the internet.
• After install, review the security checklist. Remove the default admin email, keep Joomla and all extensions updated, and enable two-factor authentication for administrators.

Backups

Capture the database and the data volume together:

1. The MariaDB database:

   docker compose exec db mysqldump -u root -p"$DB_ROOT_PASSWORD" joomla > joomla-db.sql

2. The data volume at /var/www/html (config, extensions, templates, media):

   docker run --rm -v joomla_joomla-data:/data -v "$PWD":/backup alpine \
     tar czf /backup/joomla-data.tgz -C /data .

On the RemarkableCloud App Platform, database and volume backups follow the platform’s backup schedule.

Upgrades

• New builds ship as new -r tags. Pull the new tag and recreate the container; Joomla runs any database migrations it needs on start:

  docker compose pull joomla && docker compose up -d joomla

• Always back up first, and keep the database dump and data archive from just before the upgrade.
• Read the changelog. Every build is listed in CHANGELOG.md with the base image digest and any behavior changes.
• Check extension compatibility across major Joomla upgrades.