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.

Run a MySQL container

Run the following command to run a MySQL container. Replace <tag> with the image variant you want to run.

$ docker run --name some-mysql -e MYSQL_ROOT_PASSWORD=my-secret-pw -d dhi.io/mysql:<tag> mysqld

Note: Unlike the official MySQL image, you must explicitly pass mysqld as the command to start the MySQL server.

Connect to MySQL from the command line client

Run the MySQL command line client against your container:

$ docker exec -it some-mysql mysql -uroot -p

Using Docker Compose

Example compose.yaml for MySQL:

services:
  db:
    image: dhi.io/mysql:<tag>
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: my-secret-pw
    command: mysqld
    volumes:
      - mysql-data:/var/lib/mysql
volumes:
  mysql-data:

Environment variables

The MySQL image uses the following environment variables for configuration. These variables only take effect when initializing a new database. If you start the container with a data directory that already contains a database, these variables are ignored.

Required variables

Optional variables

Read-only environment variables (set by the image)

Using Docker secrets

You can load the MySQL root password from a file using the MYSQL_ROOT_PASSWORD_FILE environment variable. This is useful for Docker secrets and other secret management systems.

Using Docker Compose with secrets:

services:
  mysql:
    image: dhi.io/mysql:<tag>
    secrets:
      - mysql_password
    environment:
      MYSQL_ROOT_PASSWORD_FILE: /run/secrets/mysql_password
    command: mysqld
secrets:
  mysql_password:
    file: ./mysql-password.txt

Using Docker run with a mounted file:

$ docker run --name some-mysql \
  -e MYSQL_ROOT_PASSWORD_FILE=/run/secrets/mysql_password \
  -v /path/to/password-file:/run/secrets/mysql_password:ro \
  -d dhi.io/mysql:<tag> mysqld

Note:MYSQL_ROOT_PASSWORD and MYSQL_ROOT_PASSWORD_FILE are mutually exclusive. If both are set, the container exits with an error.

Passing MySQL server options

Use the MYSQL_OPTIONS environment variable to pass additional options to the MySQL server:

$ docker run --name some-mysql \
  -e MYSQL_ROOT_PASSWORD=my-secret-pw \
  -e MYSQL_OPTIONS="--max-connections=50 --thread-cache-size=16" \
  -d dhi.io/mysql:<tag> mysqld

Alternatively, pass options directly on the command line after mysqld:

$ docker run --name some-mysql \
  -e MYSQL_ROOT_PASSWORD=my-secret-pw \
  -d dhi.io/mysql:<tag> mysqld --max-connections=50

Differences from the official MySQL image

The Docker Hardened MySQL image has a simplified entrypoint focused on security and minimal attack surface. The following features from the official MySQL image are not supported:

Creating databases and users

Since the DHI image does not support automatic database/user creation, create them manually after the container starts:

# Create a database
$ docker exec -it some-mysql mysql -uroot -p -e "CREATE DATABASE mydb;"

# Create a user with privileges
$ docker exec -it some-mysql mysql -uroot -p -e \
  "CREATE USER 'myuser'@'%' IDENTIFIED BY 'mypassword'; \
   GRANT ALL PRIVILEGES ON mydb.* TO 'myuser'@'%';"

Running initialization scripts

To run SQL scripts on container startup, execute them after the container is ready:

# Start the container
$ docker run --name some-mysql -e MYSQL_ROOT_PASSWORD=my-secret-pw -d dhi.io/mysql:<tag> mysqld

# Wait for MySQL to be ready, then run scripts
$ docker exec -i some-mysql mysql -uroot -pmy-secret-pw < /path/to/init.sql

Data persistence

Mount a volume to persist MySQL data across container restarts:

$ docker run --name some-mysql \
  -e MYSQL_ROOT_PASSWORD=my-secret-pw \
  -v mysql-data:/var/lib/mysql \
  -d dhi.io/mysql:<tag> mysqld

The MySQL data is stored in /var/lib/mysql inside the container.

Creating database dumps

Use mysqldump to create backups:

$ docker exec some-mysql mysqldump -uroot -p"$MYSQL_ROOT_PASSWORD" --all-databases > backup.sql

Restoring from dumps

Restore a database from a SQL dump:

$ docker exec -i some-mysql mysql -uroot -p"$MYSQL_ROOT_PASSWORD" < backup.sql

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 the app

• 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 build or compile applications

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.

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.

Permissions

By default image variants intended for runtime, run as the nonroot user. 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.

Privileged ports

Non-dev hardened images run as a nonroot user by default. As a result, applications in these images can't bind to privileged ports (below 1024) when running in Kubernetes or in Docker Engine versions older than 20.10. To avoid issues, configure your application to listen on port 1025 or higher inside the container, even if you map it to a lower port on the host. For example, docker run -p 80:8080 my-image will work because the port inside the container is 8080, and docker run -p 80:81 my-image won't work because the port inside the container is 81.

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.

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.