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 certbot image

This Docker Hardened Certbot image packages the core Certbot ACME client and its supporting library stack on a minimal Debian-based runtime:

• certbot CLI — the EFF ACME client for issuing, renewing, and revoking TLS certificates
• acme Python library — the ACME protocol implementation used by Certbot
• Python 3.14 runtime, provided by dhi/python
• OpenSSL, provided by dhi/pkg-openssl (FIPS-validated provider in -fips variants)

DNS authenticator plugins (certbot-dns-cloudflare, certbot-dns-route53, and so on) and server integration plugins (Apache, Nginx) are not included. For those use cases, see the upstream Certbot documentation⁠.

Run the certbot container

Check the installed version:

docker run --rm dhi.io/certbot:<VERSION>-debian13 --version

Display the full help reference:

docker run --rm dhi.io/certbot:<VERSION>-debian13 --help all

List certificates already stored in a mounted configuration directory:

docker run --rm \
  -v ./letsencrypt:/etc/letsencrypt \
  dhi.io/certbot:<VERSION>-debian13 \
  certificates

Issue a certificate

Webroot authenticator (recommended)

The webroot authenticator places a validation file inside an existing web server's document root without binding to any port itself. This approach works with the default nonroot user and does not require elevated privileges.

In the example below, your web server serves /.well-known/acme-challenge/ from ./webroot, and you mount your web server's document root into the container:

docker run --rm \
  -v ./letsencrypt:/etc/letsencrypt \
  -v ./var-lib-letsencrypt:/var/lib/letsencrypt \
  -v ./webroot:/var/www/html \
  dhi.io/certbot:<VERSION>-debian13 \
  certonly \
  --webroot \
  --webroot-path /var/www/html \
  --email [email protected] \
  --agree-tos \
  --no-eff-email \
  -d example.com

The image pre-provisions /var/log/letsencrypt and writes Certbot's debug log there. Mount -v ./letsencrypt-log:/var/log/letsencrypt if you want renewal logs to persist across container restarts.

Manual DNS authenticator

Use the manual DNS authenticator when your domain registrar does not have an automated plugin, or when running in an environment without inbound HTTP access:

docker run --rm -it \
  -v ./letsencrypt:/etc/letsencrypt \
  -v ./var-lib-letsencrypt:/var/lib/letsencrypt \
  dhi.io/certbot:<VERSION>-debian13 \
  certonly \
  --manual \
  --preferred-challenges dns \
  --email [email protected] \
  --agree-tos \
  --no-eff-email \
  -d example.com

Certbot will print a DNS TXT record to add to your zone. Once you have added it, press Enter to proceed.

Standalone authenticator

The standalone authenticator starts a temporary HTTP server on port 80 to answer the ACME challenge. Because the DHI runtime image runs as nonroot (uid 65532), binding to port 80 fails unless you take one of the following steps:

• Grant the NET_BIND_SERVICE capability:

  docker run --rm \
    --cap-add=NET_BIND_SERVICE \
    -p 80:80 \
    -v ./letsencrypt:/etc/letsencrypt \
    -v ./var-lib-letsencrypt:/var/lib/letsencrypt \
    dhi.io/certbot:<VERSION>-debian13 \
    certonly \
    --standalone \
    --email [email protected] \
    --agree-tos \
    --no-eff-email \
    -d example.com
  

  Copy

For most deployments the webroot or DNS authenticator is preferable because neither requires privileged port binding.

Persistence

Certbot reads and writes three directories that must persist between container runs:

All three paths in the DHI image are owned by uid/gid 65532 with mode 0770.

Using named volumes (recommended)

Named volumes are managed by Docker and avoid host permission issues:

docker run --rm \
  -v certbot-etc:/etc/letsencrypt \
  -v certbot-lib:/var/lib/letsencrypt \
  -v certbot-log:/var/log/letsencrypt \
  dhi.io/certbot:<VERSION>-debian13 \
  certificates

Using host bind-mounts

If you need to access the certificate files directly from the host, create the directories first and set their ownership to uid 65532:

mkdir -p ./letsencrypt ./var-lib-letsencrypt ./letsencrypt-log
chown -R 65532:65532 ./letsencrypt ./var-lib-letsencrypt ./letsencrypt-log

docker run --rm \
  -v ./letsencrypt:/etc/letsencrypt \
  -v ./var-lib-letsencrypt:/var/lib/letsencrypt \
  -v ./letsencrypt-log:/var/log/letsencrypt \
  dhi.io/certbot:<VERSION>-debian13 \
  certificates

Non-hardened images vs. Docker Hardened Images

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.

Standalone authenticator fails with "permission denied" on port 80

The runtime image runs as nonroot (uid 65532). Binding to port 80 requires a privileged port capability. Either add --cap-add=NET_BIND_SERVICE to your docker run command, or use the webroot, manual, or DNS authenticator instead, none of which bind to privileged ports.

"Permission denied" writing to /etc/letsencrypt

The /etc/letsencrypt, /var/lib/letsencrypt, and /var/log/letsencrypt directories in the image are owned by uid 65532. When using host bind-mounts, the host directories must also be owned by uid 65532. Run chown -R 65532:65532 <directory> on the host before mounting, or use named Docker volumes which do not have this constraint.

DNS plugin not found

DNS authenticator plugins such as certbot-dns-cloudflare and certbot-dns-route53 are not bundled in this image. Only the core certbot and acme packages are included. For DNS plugin support, refer to the upstream Certbot documentation⁠ for the upstream plugin images, or use the manual DNS authenticator (--manual --preferred-challenges dns) as an alternative.