How to use this image

All examples in this guide use the public image. If you've mirrored the repository for your own use (for example, to your Docker Hub namespace), update your commands to reference the mirrored image instead of the public one.

For example:

• Public image: dhi.io/<repository>:<tag>
• Mirrored image: <your-namespace>/dhi-<repository>:<tag>

For the examples, you must first use docker login dhi.io to authenticate to the registry to pull the images.

What's included in this WordPress image

This Docker Hardened WordPress image provides a complete PHP-FPM environment optimized for WordPress:

• WordPress Core: Version 6.9.x bundled in the image (optional - can be replaced with your own)
• PHP-FPM: FastCGI Process Manager on port 9000 for high-performance PHP processing (PHP CLI not included - see below)
• PHP Extensions: 50+ extensions including all WordPress requirements:
  • WordPress required: mysqli, pdo_mysql, json, curl, dom, fileinfo, hash, mbstring, openssl, xml
  • WordPress recommended: gd, imagick, exif, zip, intl, bcmath, sodium
  • Performance: Zend OPcache for PHP acceleration
  • Additional: ctype, filter, iconv, libxml, mysqlnd, PDO, pdo_sqlite, posix, session, SimpleXML, sqlite3, tokenizer, xmlreader, xmlwriter, zlib, and more
• ImageMagick: Version 7.1.2+ built from source with full image processing capabilities
• Security hardening: Runs as nonroot user (uid/gid 65532), minimal attack surface
• Optimized PHP configuration: Tuned for WordPress with appropriate upload sizes, memory limits, and execution times

The image supports two deployment approaches:

1. Bundled WordPress (Quick Start): Use the WordPress version included in the image
2. Custom WordPress (Production): Mount your own WordPress sources for full version control

Note: PHP-FPM runs on port 9000 and requires a web server (nginx, Apache, Caddy) to handle HTTP requests and proxy to PHP-FPM.

Start a WordPress instance

Quick start with bundled WordPress

The simplest way to get started uses the WordPress version bundled in the image:

docker run -d \
  --name wordpress \
  -p 9000:9000 \
  dhi.io/wordpress:<tag>

Note: This starts PHP-FPM on port 9000. You'll need a web server to proxy HTTP requests to it (see complete stack example below).

Production setup with custom WordPress

For production environments, mount your own WordPress sources:

docker run -d \
  --name wordpress \
  -v $(pwd)/wordpress:/var/www/html \
  -p 9000:9000 \
  dhi.io/wordpress:<tag>

This approach:

• Keeps WordPress sources in version control
• Allows independent control of WordPress updates
• Uses the image purely for PHP runtime and extensions
• Works with any WordPress version (not limited to 6.9)

Common WordPress use cases

Complete WordPress stack with nginx and MySQL

WordPress requires both a web server and database. This example provides a complete stack:

Note: Create the nginx.conf file using the configuration shown below before running docker compose up.

services:
  db:
    image: dhi.io/mysql:8.4
    command: mysqld
    environment:
      MYSQL_ROOT_PASSWORD: rootsecret
    volumes:
      - db_data:/var/lib/mysql
    healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "127.0.0.1", "-uroot", "-prootsecret"]
      interval: 2s
      timeout: 3s
      retries: 30

  db-init:
    image: dhi.io/mysql:8.4
    depends_on:
      db:
        condition: service_healthy
    command: >
      bash -c "mysql -h db -uroot -prootsecret <<EOF
        CREATE DATABASE IF NOT EXISTS wordpress;
        CREATE USER IF NOT EXISTS 'wordpress'@'%' IDENTIFIED BY 'changeme';
        GRANT ALL PRIVILEGES ON wordpress.* TO 'wordpress'@'%';
        FLUSH PRIVILEGES;
      EOF"
    restart: "no"

  wordpress:
    image: dhi.io/wordpress:<tag>
    volumes:
      - wordpress-data:/var/www/html
    environment:
      WORDPRESS_DB_HOST: db
      WORDPRESS_DB_NAME: wordpress
      WORDPRESS_DB_USER: wordpress
      WORDPRESS_DB_PASSWORD: changeme
    depends_on:
      db-init:
        condition: service_completed_successfully

  nginx:
    image: dhi.io/nginx:1
    ports:
      - "80:80"
    volumes:
      - wordpress-data:/var/www/html:ro
      - ./nginx.conf:/etc/nginx/nginx.conf:ro
    depends_on:
      - wordpress

volumes:
  wordpress-data:
  db_data:

The db-init service runs once to create the WordPress database and user, then exits. WordPress waits for this initialization to complete before starting.

Example nginx configuration for WordPress (nginx.conf):

Note: This image does not include .htaccess files since they are Apache-specific and have no effect with nginx or PHP-FPM. The configuration below provides equivalent WordPress routing using nginx directives.

Important: The DHI nginx image runs as nonroot and requires the PID file directive to use a writable location.

pid /tmp/nginx.pid;

events {
    worker_connections 1024;
}

http {
    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    server {
        listen 80;
        server_name example.com;
        root /var/www/html;
        index index.php;

        location / {
            # WordPress permalinks - equivalent to .htaccess rewrite rules
            try_files $uri $uri/ /index.php?$args;
        }

        location ~ \.php$ {
            fastcgi_pass wordpress:9000;
            fastcgi_index index.php;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
            # Pass HTTP_AUTHORIZATION header (WordPress requirement)
            fastcgi_param HTTP_AUTHORIZATION $http_authorization;
            include fastcgi_params;
        }

        location ~* \.(jpg|jpeg|png|gif|ico|css|js|svg|woff|woff2|ttf|eot)$ {
            expires 30d;
            add_header Cache-Control "public, immutable";
        }

        location ~ /\.ht {
            deny all;
        }
    }
}

Adding custom PHP extensions

The image includes 50+ PHP extensions for WordPress. If you need additional extensions (e.g., redis, mongodb), use a multi-stage build using dhi/php as the builder base.

# Stage 1: Compile extension using dev variant
FROM dhi.io/php:8.3-dev as builder

# Add any additional  
RUN set -eux; \
    apt-get update && \
    apt-get install -y --no-install-recommends \
        git \
        libpcre2-dev && \
    cd /tmp && \
    git clone https://github.com/krakjoe/apcu.git && \
    cd apcu && \
    phpize && \
    ./configure --enable-apcu && \
    make && \
    make install && \
    # Copy compiled extension to staging
    mkdir -p /extensions && \
    cp $(php-config --extension-dir)/apcu.so /extensions/ && \
    # Create config file
    mkdir -p /ext-config && \
    echo "extension=apcu.so" > /ext-config/docker-php-ext-apcu.ini

# Stage 2: Runtime image with extension
FROM dhi.io/wordpress:6.9-php8.3-fpm

ARG PHP_EXT_DIR=/opt/php-8.3/lib/php/extensions/no-debug-non-zts-20230831
ARG PHP_CONF_DIR=/opt/php-8.3/etc/php/conf.d

# Copy both extension binary and config
COPY --from=builder /extensions/apcu.so "${PHP_EXT_DIR}/"
COPY --from=builder /ext-config/docker-php-ext-apcu.ini "${PHP_CONF_DIR}/"

Docker Official Images vs. Docker Hardened Images

Key differences

Why no shell or package manager?

Docker Hardened Images prioritize security through minimalism:

• Reduced attack surface: Fewer binaries mean fewer potential vulnerabilities
• Immutable infrastructure: Runtime containers shouldn't be modified after deployment
• Compliance ready: Meets strict security requirements for regulated environments

The hardened images intended for runtime don't contain a shell nor any tools for debugging. Common debugging methods for applications built with Docker Hardened Images include:

• Docker Debug⁠ to attach to containers
• Docker's Image Mount feature to mount debugging tools
• WP-CLI in a separate container for WordPress management

For example, you can use Docker Debug:

docker debug wordpress

or mount debugging tools with the Image Mount feature:

docker run --rm -it --pid container:wordpress \
  --mount=type=image,source=dhi.io/busybox,destination=/dbg,ro \
  dhi.io/wordpress:<tag> /dbg/bin/sh

Image variants

Docker Hardened Images come in different variants depending on their intended use.

Runtime variants are designed to run your application in production. These images are intended to be used either directly or as the FROM image in the final stage of a multi-stage build. These images typically:

• Run as the nonroot user
• Do not include a shell or a package manager
• Contain only the minimal set of libraries needed to run WordPress

Build-time variants typically include dev in the variant name and are intended for use in the first stage of a multi-stage Dockerfile. These images typically:

• Run as the root user
• Include a shell and package manager
• Are used to install additional PHP extensions or customize the environment

FIPS variants include fips in the variant name and tag. They come in both runtime and build-time variants. These variants use cryptographic modules that have been validated under FIPS 140, a U.S. government standard for secure cryptographic operations.

Migrate to a Docker Hardened Image

To migrate your application to a Docker Hardened Image, you must update your Dockerfile. At minimum, you must update the base image in your existing Dockerfile to a Docker Hardened Image. This and a few other common changes are listed in the following table of migration notes.

The following steps outline the general migration process.

1. Find hardened images for your app.

   A hardened image may have several variants. Inspect the image tags and find the image variant that meets your needs. WordPress images are available with PHP 8.3 and 8.4.

2. Update the base image in your Dockerfile.

   Update the base image in your application's Dockerfile to the hardened image you found in the previous step. For framework images, this is typically going to be an image tagged as dev because it has the tools needed to install packages and dependencies.

3. For multi-stage Dockerfiles, update the runtime image in your Dockerfile.

   To ensure that your final image is as minimal as possible, you should use a multi-stage build. All stages in your Dockerfile should use a hardened image. While intermediary stages will typically use images tagged as dev, your final runtime stage should use a non-dev image variant.

4. Install additional packages

   Docker Hardened Images contain minimal packages in order to reduce the potential attack surface. You may need to install additional packages in your Dockerfile. Inspect the image variants to identify which packages are already installed.

   Only images tagged as dev typically have package managers. You should use a multi-stage Dockerfile to install the packages. Install the packages in the build stage that uses a dev image. Then, if needed, copy any necessary artifacts to the runtime stage that uses a non-dev image.

   For Alpine-based images, you can use apk to install packages. For Debian-based images, you can use apt-get to install packages.

Troubleshooting migration

The following are common issues that you may encounter during migration.

General debugging

The hardened images intended for runtime don't contain a shell nor any tools for debugging. The recommended method for debugging applications built with Docker Hardened Images is to use Docker Debug⁠ to attach to these containers. Docker Debug provides a shell, common debugging tools, and lets you install other tools in an ephemeral, writable layer that only exists during the debugging session.

For WordPress-specific debugging:

# View PHP-FPM logs
docker logs wordpress

# Use Docker Debug for interactive troubleshooting
docker debug wordpress

# Check PHP-FPM configuration
docker exec wordpress php-fpm -i | grep -i wordpress

Permissions

By default image variants intended for runtime, run as the nonroot user (uid/gid 65532). Ensure that necessary files and directories are accessible to the nonroot user. You may need to copy files to different directories or change permissions so your application running as the nonroot user can access them.

For WordPress specifically:

• wp-content/uploads must be writable for media uploads
• wp-content/plugins and wp-content/themes must be writable if installing via WordPress admin
• wp-config.php should be readable but not writable for security

Set permissions correctly:

# Make uploads directory writable
chown -R 65532:65532 wordpress/wp-content/uploads
chmod -R 755 wordpress/wp-content/uploads

# For plugin/theme installation via admin
chown -R 65532:65532 wordpress/wp-content/plugins
chown -R 65532:65532 wordpress/wp-content/themes

Privileged ports

Non-dev hardened images run as a nonroot user by default. PHP-FPM's default port 9000 is not affected by this limitation and works without any special configuration. Your web server (nginx, Apache) will bind to ports 80/443, not the WordPress container.

Entry point

Docker Hardened Images may have different entry points than images such as Docker Official Images. Use docker inspect to inspect entry points for Docker Hardened Images and update your Dockerfile if necessary.

The WordPress image uses php-fpm as its entry point. If you need to customize the entry point, ensure PHP-FPM continues to run in the foreground.

No shell

By default, image variants intended for runtime don't contain a shell. Use dev images in build stages to run shell commands and then copy any necessary artifacts into the runtime stage. In addition, use Docker Debug to debug containers with no shell.