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.

Start a Tomcat instance

Run the following command to run the Tomcat server. Replace <tag> with the image variant you want to run.

$ docker run -p 8080:8080 -d dhi.io/tomcat:<tag>

Note that visiting http://localhost:8080⁠ will return a 404 as no webapps are loaded by default.

Deploy a web application

There are two common ways to deploy a .war file.

The first way is to mount into webapps/:

$ docker run -p 8080:8080 \
    -v $(pwd)/myapp.war:/usr/local/tomcat/webapps/myapp.war \
    -d dhi.io/tomcat:<tag>

The second way is to build a new image that adds the .war file to webapps/:

FROM dhi.io/tomcat:<tag>
COPY myapp.war /usr/local/tomcat/webapps/

Persist logs and configuration

The configuration files are available in /usr/local/tomcat/conf/.

To capture logs or provide your own Tomcat configuration files, mount a volume into the container:

$ docker run -p 8080:8080 \
    -v $(pwd)/logs:/usr/local/tomcat/logs \
    -v $(pwd)/server.xml:/usr/local/tomcat/conf/server.xml \
    -d dhi.io/tomcat:<tag>

Non-hardened 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 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

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 example, you can use Docker Debug:

docker debug <image-name>

or mount debugging tools with the Image Mount feature:

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

FIPS variants

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. In attestations you will see two crypto module information blocks: one for OpenSSL FIPS (system TLS) and one for the language runtime (for example, BouncyCastle FIPS in Java).

Migrate to a Docker Hardened Image

Switching to the hardened Tomcat image does not require any special changes. You can use it as a drop-in replacement for the standard Tomcat image in your existing workflows and configurations.

Migration steps

1. Update your image reference. For example:

   • From: tomcat:<tag>
   • To: dhi.io/tomcat:<tag>

2. Review environment variables usage.

   Docker Hardened Tomcat images keep the same directory layout (/usr/local/tomcat) and default behavior as the standard image, so most mounts and configurations work unchanged. However, environment variables differ slightly: this image uses JAVA_HOME (Temurin) instead of the DOI's JRE_HOME. If your scripts reference JRE_HOME, switch to JAVA_HOME (or export JRE_HOME=$JAVA_HOME for compatibility).

3. Runtime variants run as a non-root user and do not include a package manager. In most Tomcat use cases, you won't need to install extra packages, just deploy your .war files as usual. If your application requires native libraries or build tools, use the dev variant in build stages to install them, and copy the built artifacts into a runtime image.

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.