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 PostgreSQL image

This Docker Hardened PostgreSQL image includes the complete PostgreSQL database system in a single, security-hardened package.

To see the complete list of available PostgreSQL tools, you can check the /usr/lib/postgresql/<VERSION>/bin/ directory inside the container (replace <VERSION> with your PostgreSQL version, e.g., 15 or 16).

Unlike some other DHI images where runtime variants contain only the main binary, the PostgreSQL runtime image includes all PostgreSQL tools. This design decision delivers maximum operational flexibility:

• Database administration tasks require tools like psql in production
• Backup and restore operations need pg_dump and pg_restore
• Operational tasks often require these tools to be available
• This bundling provides a complete PostgreSQL toolkit in one security-hardened package

This approach aligns with real-world production use cases where PostgreSQL operations require more than just the server binary.

Start a PostgreSQL instance

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

docker run --name some-postgres -e POSTGRES_PASSWORD=mysecretpassword -d dhi.io/postgres:<tag>

Common PostgreSQL use cases

Basic PostgreSQL server with client access

Start the PostgreSQL:

docker run --name my-postgres -e POSTGRES_PASSWORD=mysecretpassword -d dhi.io/postgres:<tag>

Connect using the bundled psql:

docker exec -it my-postgres psql -U postgres

PostgreSQL with network connectivity

Create a network and run PostgreSQL:

# Create a custom network
docker network create app-network

# Run PostgreSQL on the network
docker run --name my-postgres -d \
  --network app-network \
  -e POSTGRES_PASSWORD=mysecretpassword \
  dhi.io/postgres:<tag>

Applications running in Docker containers on the same network can now connect using 'my-postgres' as the hostname. For example: postgres://postgres:mysecretpassword@my-postgres:5432/postgres.

If your application is running outside Docker, use localhost or 127.0.0.1 with the exposed port instead.

Database backup and restore

Use the bundled tools for backup operations.

Create a backup:

docker exec my-postgres pg_dump -U postgres dbname > backup.sql

Restore a backup:

docker exec -i my-postgres psql -U postgres dbname < backup.sql

Configure PostgreSQL with environment variables

The PostgreSQL image uses several environment variables for configuration:

Required variables

POSTGRES_PASSWORD: Sets the superuser password for PostgreSQL. This variable is required and must not be empty.

Optional variables

• POSTGRES_USER: Specifies a user with superuser privileges and creates a database with the same name. Defaults to postgres if not specified.
• POSTGRES_DB: Defines a different name for the default database. If not specified, uses the value of POSTGRES_USER.
• POSTGRES_INITDB_ARGS: Sends arguments to postgres initdb (space-separated string).
• POSTGRES_INITDB_WALDIR: Relocates pg_wal if specified. Equivalent to --waldir in POSTGRES_INITDB_ARGS.
• POSTGRES_HOST_AUTH_METHOD: Controls the auth-method for host connections. Supported values are scram-sha-256 and md5 (default). The values trust and password are not supported for security reasons.

Note: Authentication method restrictions are enforced only during database initialization by the entrypoint script. If a database is initialized with another image and then run with the DHI, these security protections may be bypassed.

Read-only environment variables (set by the image)

• PG_MAJOR: Contains the PostgreSQL major version number (e.g., 15, 16, 17). This variable is automatically set by the image and should not be overridden.
• PG_MINOR: Contains the PostgreSQL minor version number. This variable is automatically set by the image and should not be overridden.
• PGDATA: Automatically set to /var/lib/postgresql/<MAJOR_VERSION>/data. Note that when mounting volumes, the best practice is to mount to /var/lib/postgresql (the parent directory), not to the PGDATA path directly.

Example with multiple environment variables:

docker run --name postgres-configured -d \
  -e POSTGRES_USER=myuser \
  -e POSTGRES_PASSWORD=mypassword \
  -e POSTGRES_DB=mydb \
  -e POSTGRES_INITDB_ARGS="--encoding=UTF8 --locale=C" \
  dhi.io/postgres:<tag>

Persisting data with volumes

Mount to /var/lib/postgresql (recommended)

The recommended approach is to mount your volume to /var/lib/postgresql rather than directly to the versioned PGDATA directory:

docker run --name my-postgres -d \
  -e POSTGRES_PASSWORD=mysecretpassword \
  -v postgres-data:/var/lib/postgresql \
  dhi.io/postgres:<tag>

This is the preferred method because it:

• Supports upgrade workflows: Multiple PostgreSQL major versions can coexist in the same volume, making upgrades between major versions easier
• Follows PostgreSQL best practices: Aligns with the pattern used by Docker Official Images and recommended by PostgreSQL maintainers
• Ensures future compatibility: Your volume mount commands don't need to change when you upgrade PostgreSQL major versions

With this approach, the image automatically creates the versioned subdirectory inside your mounted volume.

Mount directly to PGDATA

While mounting directly to the versioned PGDATA path works, it's generally not recommended:

# Not recommended for most use cases
docker run --name my-postgres -d \
  -e POSTGRES_PASSWORD=mysecretpassword \
  -v postgres-data:/var/lib/postgresql/16/data \
  dhi.io/postgres:16

Use direct PGDATA mounting only when you have specific requirements that necessitate it, such as very specialized deployment patterns or when migrating from existing setups.

Stop PostgreSQL containers

The Docker Hardened PostgreSQL image is configured to use SIGINT as its stop signal instead of Docker's default SIGTERM. This PostgreSQL-specific configuration ensures clean database shutdown with proper checkpoint completion.

PostgreSQL shutdown modes

PostgreSQL responds to different signals with different shutdown behaviors:

• SIGINT (used by DHI): Initiates a "fast" shutdown. Refuses new connections, aborts active transactions, and performs a checkpoint before stopping.
• SIGTERM (OCI default): Initiates a "smart" shutdown. Waits for all clients to disconnect, which could take indefinitely.
• SIGQUIT: Forces immediate shutdown without checkpoint (not recommended).

Stop containers for DHI

When you stop a DHI PostgreSQL container, Docker automatically sends SIGINT due to the image configuration:

docker stop my-postgres

Docker will:

1. Send SIGINT to PostgreSQL.
2. Wait for the stop timeout (default 10 seconds).
3. Force kill with SIGKILL if not stopped.

Adjust stop timeout for large databases

For databases with significant data that need more checkopoint time, give PostgreSQL 30 seconds to complete shutdown:

docker stop -t 30 my-postgres

Why this matters for data integrity

The SIGINT configuration ensures:

• All committed transactions are safely written to disk
• Proper checkpoint completion before shutdown
• Faster recovery on next startup
• Reduced risk of data corruption

This is especially important in production environments where data integrity is critical.

Docker Official Images vs. Docker Hardened Images

Key differences

Why no 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 package manager 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
• Ecosystem-specific debugging approaches

For example, you can use Docker Debug:

docker debug my-postgres

or mount debugging tools with the Image Mount feature:

docker run --rm -it --pid container:my-postgres \
  --mount=type=image,source=dhi.io/busybox,destination=/dbg,ro \
  dhi.io/postgres:<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 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.

5. Update volume mounts for PGDATA.

   The recommended approach is to mount volumes to the parent directory /var/lib/postgresql, which supports upgrade workflows:

   # Recommended: Update docker-compose.yml or docker run commands
   volumes:
     - postgres-data:/var/lib/postgresql
   

   Copy

   This allows the image to automatically manage the versioned subdirectories and makes major version upgrades easier.

Troubleshooting migration

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

General debugging

The hardened images intended for runtime don't contain 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 PostgreSQL-specific debugging, you can still access PostgreSQL's built-in monitoring.

View active connections and queries:

docker exec my-postgres psql -U postgres -c "SELECT * FROM pg_stat_activity;"

Check PostgreSQL logs (location varies by configuration)"

docker logs my-postgres

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.

For PostgreSQL, the data directory and configuration files must have appropriate ownership. The image handles this automatically for the default PGDATA location, but custom mounted files may need permission adjustments.

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.

PostgreSQL's default port 5432 is not affected by this limitation and works without any special configuration.

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.

PGDATA migration from Docker Official Images

When migrating existing PostgreSQL deployments from Docker Official Images or other PostgreSQL images (such as Bitnami PostgreSQL, postgres:alpine, or custom images), you need to account for different data directory patterns:

• Docker Official Images PostgreSQL ≤17: /var/lib/postgresql/data (non-versioned)
• Docker Official Images PostgreSQL 18+: /var/lib/postgresql/<MAJOR>/docker (versioned)
• Docker Hardened Images all versions: /var/lib/postgresql/<MAJOR_VERSION>/data (versioned)

Regardless of the source, the recommended approach for both DOI and DHI is to mount volumes to /var/lib/postgresql.

Versioned PGDATA paths

The DHI PostgreSQL image uses a versioned data directory pattern (/var/lib/postgresql/${PG_MAJOR}/data) that's automatically determined by the PostgreSQL major version in the image. This means:

• PostgreSQL 15.x images use /var/lib/postgresql/15/data
• PostgreSQL 16.x images use /var/lib/postgresql/16/data
• PostgreSQL 17.x images use /var/lib/postgresql/17/data
• PostgreSQL 18.x images use /var/lib/postgresql/18/data

This versioning is controlled by the PG_MAJOR environment variable that's built into the image. When writing scripts or configurations, you may reference the version dynamically:

docker exec my-postgres sh -c 'echo "Data directory: $PGDATA"'
docker exec my-postgres sh -c 'echo "Major version: $PG_MAJOR"'

This helps prevent accidental data directory mismatches when upgrading PostgreSQL versions.

Migration options

For new deployments, mount to the parent directory to support upgrade workflows:

# Old (Docker Official PostgreSQL ≤17)
-v postgres-data:/var/lib/postgresql/data

# Recommended (both DOI 18+ and DHI all versions)
-v postgres-data:/var/lib/postgresql

The image will automatically create the versioned subdirectory inside your mounted volume:

• DHI: 16/data, 17/data, etc.
• DOI 18+: 18/docker, 19/docker, etc.

For existing data migration, choose an option:

• Option 1: Data export/import (recommended for production)

  Export from old container:

  docker exec old-postgres pg_dumpall -U postgres > backup.sql
  

  Copy

  Import to new DHI container:

  docker exec -i new-postgres psql -U postgres < backup.sql
  

  Copy

• Option 2: Direct data copy

  Stop old container:

  docker stop old-postgres
  

  Copy

  Copy data to a new location with versioned subdirectory (replace 16 with your major version):

  docker run --rm \
    -v old-postgres-data:/old \
    -v new-postgres-data:/new \
    busybox sh -c "cp -a /old/. /new/16/data/"
  

  Copy

  Start new DHI container with parent directory mount:

  docker run --name new-postgres -d \
    -e POSTGRES_PASSWORD=mysecretpassword \
    -v new-postgres-data:/var/lib/postgresql \
    dhi.io/postgres:16
  

  Copy

  This approach mounts the volume to /var/lib/postgresql, which will contain the 16/data subdirectory with your migrated data. This makes future major version upgrades easier.