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/httpd:<tag>
• Mirrored image: <your-namespace>/dhi-httpd:<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 httpd image

This Docker Hardened httpd image includes:

• httpd — Apache HTTP Server daemon
• httpd-foreground — Wrapper script used to run httpd in the foreground inside containers
• apachectl — Control interface for the Apache HTTP Server

Start a httpd image

Basic usage

$ docker run -d --name my-httpd -p 8080:8080 \
  dhi.io/httpd:<tag>

This starts the httpd runtime variant and maps the container's HTTP port (8080) to the host.

With Docker Compose (recommended for complex setups)

version: '3.8'
services:
  httpd:
    image: dhi.io/httpd:<tag>
    container_name: my-httpd
    ports:
      - "8080:8080"
    environment:
      - HTTPD_PREFIX=/usr/local/apache2
    volumes:
      - ./website:/usr/local/apache2/htdocs:ro

Environment variables

Example with environment variables:

$ docker run -d --name my-httpd -p 8080:8080 \
  -e HTTPD_PREFIX=/usr/local/apache2 \
  dhi.io/httpd:<tag>

Common httpd use cases

• Basic server: serve static content from a mounted host directory. Example:

  docker run -d -p 8080:8080 \
    -v $(pwd)/website:/usr/local/apache2/htdocs:ro \
    dhi.io/httpd:<tag>
  

  Copy

• Server with custom configuration: mount httpd.conf or extra configuration files into the container. Example:

  docker run -d -p 8080:8080 \
    -v $(pwd)/httpd.conf:/usr/local/apache2/conf/httpd.conf:ro \
    dhi.io/httpd:<tag>
  

  Copy

• Server with TLS/SSL: The default httpd-ssl.conf uses Listen 443, which won't work with the nonroot user. You must provide a custom SSL config that uses a non-privileged port (e.g., 8443). Mount your cert, key, and modified SSL config:

  docker run -d -p 8443:8443 \
    -v /path/to/server.crt:/usr/local/apache2/conf/server.crt:ro \
    -v /path/to/server.key:/usr/local/apache2/conf/server.key:ro \
    -v /path/to/httpd-ssl.conf:/usr/local/apache2/conf/extra/httpd-ssl.conf:ro \
    dhi.io/httpd:<tag>
  

  Copy

  Your custom httpd-ssl.conf should include Listen 8443 instead of Listen 443.

Enabling additional modules

This image includes commonly needed modules that are built but not loaded by default. This keeps the default configuration minimal while allowing you to enable additional functionality as needed.

Available modules (not loaded by default)

The following modules are built and available at /usr/local/apache2/modules/:

How to enable modules

To enable a module, add a LoadModule directive to your custom httpd.conf:

# Enable URL rewriting
LoadModule rewrite_module modules/mod_rewrite.so

# Enable gzip compression
LoadModule deflate_module modules/mod_deflate.so

# Enable reverse proxy (requires both modules)
LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_http_module modules/mod_proxy_http.so

Example: Enable mod_rewrite for URL rewriting

Create a custom configuration file (httpd-custom.conf):

ServerRoot "/usr/local/apache2"
Listen 8080

# Core modules (required)
LoadModule mpm_event_module modules/mod_mpm_event.so
LoadModule unixd_module modules/mod_unixd.so
LoadModule authz_core_module modules/mod_authz_core.so
LoadModule dir_module modules/mod_dir.so
LoadModule mime_module modules/mod_mime.so
LoadModule log_config_module modules/mod_log_config.so

# Enable rewrite module
LoadModule rewrite_module modules/mod_rewrite.so

User www-data
Group www-data

ServerName localhost
ErrorLog /proc/self/fd/2
CustomLog /proc/self/fd/1 common
LogFormat "%h %l %u %t \"%r\" %>s %b" common

DocumentRoot "/usr/local/apache2/htdocs"
<Directory "/usr/local/apache2/htdocs">
    Options FollowSymLinks
    AllowOverride All
    Require all granted

    # Example rewrite rule
    RewriteEngine On
    RewriteRule ^old-page\.html$ /new-page.html [R=301,L]
</Directory>

DirectoryIndex index.html
TypesConfig conf/mime.types

Run with the custom configuration:

docker run -d -p 8080:8080 \
  -v $(pwd)/httpd-custom.conf:/usr/local/apache2/conf/httpd.conf:ro \
  -v $(pwd)/website:/usr/local/apache2/htdocs:ro \
  dhi.io/httpd:<tag>

Verify modules are loaded

To check which modules are currently loaded:

docker run --rm --entrypoint httpd dhi.io/httpd:<tag> -M

Troubleshooting

Check configuration syntax

Test a mounted configuration before starting the container:

docker run --rm \
  -v $(pwd)/httpd.conf:/usr/local/apache2/conf/httpd.conf:ro \
  --entrypoint httpd \
  dhi.io/httpd:<tag> \
  -t

This runs httpd's configuration test and reports syntax errors.

Debug mode (foreground)

Run Apache in the foreground with verbose/debug logging to the console:

docker run --rm -p 8080:8080 \
  --entrypoint httpd \
  dhi.io/httpd:<tag> \
  -DFOREGROUND -e debug

Use this for interactive troubleshooting; logs go to stdout/stderr so you can see them with docker logs.

Access a shell for debugging

The httpd runtime image includes a minimal shell (/bin/sh). To open a shell:

docker run --rm -it --entrypoint /bin/sh dhi.io/httpd:<tag>

For more comprehensive debugging tools, use docker debug or the -dev variant.

Verify apachectl and binaries

Confirm apachectl (and other Apache binaries) exist at runtime:

docker run --rm --entrypoint /bin/sh dhi.io/httpd:<tag> -c "command -v /usr/local/apache2/bin/apachectl && command -v /usr/local/apache2/bin/httpd || true"

If apachectl is available you can use it with care (note that in containers the recommended pattern is to run httpd in the foreground):

# show apachectl help
docker run --rm --entrypoint /usr/local/apache2/bin/apachectl dhi.io/httpd:<tag> -h

View logs

Use docker logs for the container to view combined stdout/stderr (Apache has been configured to log to stdout/stderr):

docker logs my-httpd

Non-hardened images vs. Docker Hardened Images

The following notes highlight key, tangible differences between the upstream (non-hardened) httpd image and this Docker Hardened Image:

• Non-root user: The Docker Hardened httpd runtime variant runs as a nonroot user (www-data). Ensure any mounted files and directories have appropriate ownership/permissions for the nonroot user.

• Internal listening port: The upstream httpd image listens on port 80. The DHI listens on port 8080 (to avoid privileged ports which require root). Update your port mappings from -p 80:80 to -p 80:8080 or -p 8080:8080.

• Minimal runtime: Runtime variants are minimal and may omit shells and package managers. Use dev variants (tags with dev) for build-time or debugging workflows.

• Entrypoint: The upstream image uses CMD ["httpd-foreground"] with no entrypoint. The DHI uses ENTRYPOINT ["httpd-foreground"] with no cmd. This means arguments passed to docker run are appended to httpd-foreground rather than replacing the command. Use --entrypoint to run other commands (e.g., --entrypoint httpd ... -t).

Image variants

Docker Hardened Images come in different variants depending on their intended use. Image variants are identified by their tag.

• 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 a 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 tag 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

• 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. For example, usage of MD5 fails in FIPS variants.

To view the image variants and get more information about them, select the Tags tab for this repository, and then select a tag.

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.