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

This image builds S3Proxy from source and runs it on the Eclipse Temurin JRE. It ships the S3Proxy jar together with the upstream run-docker-container.sh launcher, so the same S3PROXY_* and JCLOUDS_* environment variables used by the upstream andrewgaul/s3proxy image continue to work. See the S3Proxy documentation⁠ for the full list of configuration options and storage backends.

Run the container

Run the following command to start S3Proxy with its default filesystem backend:

$ docker run -d --name s3proxy -p 8080:8080 dhi.io/s3proxy:<tag>

S3Proxy listens on port 8080 inside the container and, by default, requires AWS Signature v2 or v4 signed requests using the identity local-identity and credential local-credential. An unauthenticated request to / returns an S3 AccessDenied (HTTP 403) response, which confirms the service is up. Objects are stored on the local filesystem under /data.

Ports

The upstream andrewgaul/s3proxy image listens on privileged port 80 because it runs as root. Docker Hardened Images run as the nonroot user (uid 65532), which cannot bind ports below 1024, so this image defaults S3PROXY_ENDPOINT to http://0.0.0.0:8080. Map it to whatever host port you need, for example -p 80:8080. To change the in-container port, override S3PROXY_ENDPOINT (keep it at 1024 or higher).

Configuration

S3Proxy is configured through environment variables that the launcher maps to Java system properties. The most common ones are:

For example, to disable authorization and use an anonymous S3 endpoint:

$ docker run -d --name s3proxy \
  -p 8080:8080 \
  -e S3PROXY_AUTHORIZATION=none \
  dhi.io/s3proxy:<tag>

Persisting data

The filesystem backend stores buckets and objects under /data. Mount a volume there to persist data across container restarts:

$ docker run -d --name s3proxy \
  -p 8080:8080 \
  -v s3proxy-data:/data \
  dhi.io/s3proxy:<tag>

Proxying to another backend

Point S3Proxy at a different jclouds backend, for example Google Cloud Storage, by overriding the provider and credentials:

$ docker run -d --name s3proxy \
  -p 8080:8080 \
  -e JCLOUDS_PROVIDER=google-cloud-storage \
  -e JCLOUDS_IDENTITY=<service-account> \
  -e JCLOUDS_CREDENTIAL=<private-key> \
  dhi.io/s3proxy:<tag>

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

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.

This image keeps the upstream dumb-init entry point and the run-docker-container.sh launcher, so the S3PROXY_* and JCLOUDS_* environment variables behave the same as the upstream andrewgaul/s3proxy image. The one intentional difference is the default listen port, which is 8080 instead of the upstream 80 because the image runs as the nonroot user (see Ports⁠).