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.

Refer to the upstream Varnish Cache documentation⁠ for complete VCL syntax and configuration options.

What's included in this Varnish image

This Docker Hardened Varnish image includes:

• varnishd — HTTP accelerator daemon (container entry point)
• varnishadm — CLI for the varnishd management interface
• varnishlog — Live viewer for shared-memory (SHMLOG) request logs
• varnishstat — Runtime counters and statistics
• varnishhist — Terminal histogram of request latencies from SHMLOG
• varnishncsa — NCSA-style access logs from SHMLOG
• varnishtop — Top-like view of the most frequent SHMLOG tags
• varnishtest — Varnish Test Case (VTC) harness

All of the above are installed under /usr/local/bin/.

Start a varnish image

Basic usage

Replace <tag> with the image variant you want (for example 9.0, 8.0, or 9.0.1-debian13).

docker run -p 8080:8080 -p 8443:8443 dhi.io/varnish:<tag>

The default configuration listens on 8080 (HTTP) and 8443 (PROXY), uses /etc/varnish/default.vcl, enables HTTP/2, and uses malloc,100M storage.

Mount your own VCL:

docker run -p 8080:8080 -p 8443:8443 \
  -v /path/to/default.vcl:/etc/varnish/default.vcl:ro \
  dhi.io/varnish:<tag>

With Docker Compose (recommended for complex setups)

services:
  varnish:
    image: dhi.io/varnish:<tag>
    ports:
      - "8080:8080"
      - "8443:8443"
    volumes:
      - ./default.vcl:/etc/varnish/default.vcl:ro
    tmpfs:
      - /var/lib/varnish:exec

A tmpfs on /var/lib/varnish is recommended for low-latency SHM log workloads.

Common Varnish Cache use cases

HTTP reverse proxy cache

Create a default.vcl pointing at an upstream origin:

vcl 4.1;

backend default {
    .host = "origin.example.com";
    .port = "80";
}

sub vcl_recv {
    if (req.method == "PURGE") {
        return (purge);
    }
}

docker run -p 8080:8080 -p 8443:8443 \
  -v $(pwd)/default.vcl:/etc/varnish/default.vcl:ro \
  dhi.io/varnish:<tag>

Adjust cache storage size

By default the image starts varnishd with -s malloc,100M. To change the cache size, override the container command with a full varnishd argument list:

docker run -p 8080:8080 -p 8443:8443 dhi.io/varnish:<tag> \
  -F -f /etc/varnish/default.vcl \
  -a http=:8080,HTTP -a proxy=:8443,PROXY \
  -p feature=+http2 \
  -s malloc,1G

Observability tools (varnishlog, varnishstat, …)

Prefer docker exec against a running cache:

docker exec -it <container> /usr/local/bin/varnishlog
docker exec -it <container> /usr/local/bin/varnishstat

For a one-off docker run that runs a tool binary (similar to the Docker Official Image entrypoint), set --entrypoint:

docker run --rm --entrypoint /usr/local/bin/varnishlog dhi.io/varnish:<tag>

Varnish admin CLI (varnishadm)

varnishadm requires -T and -S on varnishd. The default command does not enable the management interface; start the cache with management enabled:

openssl rand -base64 32 > varnish-secret
chmod 644 varnish-secret

docker run -d --name varnish -p 8080:8080 -p 8443:8443 \
  -v $(pwd)/varnish-secret:/etc/varnish/secret:ro \
  dhi.io/varnish:<tag> \
  -F -f /etc/varnish/default.vcl \
  -a http=:8080,HTTP -a proxy=:8443,PROXY \
  -p feature=+http2 \
  -s malloc,100M \
  -T 127.0.0.1:6082 \
  -S /etc/varnish/secret

docker exec -it varnish /usr/local/bin/varnishadm \
  -T 127.0.0.1:6082 \
  -S /etc/varnish/secret \
  ping

Binding -T to 127.0.0.1 keeps the management interface off the container network; only docker exec (or the same network namespace) can reach it.

Non-hardened images vs. Docker Hardened Images

Key differences

Replacing Docker Hub varnish (official image)

The hardened image matches the typical official workload (varnishd in the foreground, default VCL path, HTTP/2, malloc storage, HTTP + PROXY listeners) but not the official container API:

Equivalent to the official default prefix (already the image default CMD; shown for migration from Compose that called the wrapper):

docker run -p 8080:8080 -p 8443:8443 dhi.io/varnish:<tag> \
  -F -f /etc/varnish/default.vcl \
  -a http=:8080,HTTP -a proxy=:8443,PROXY \
  -p feature=+http2 \
  -s malloc,100M

The official image sets VSM_NOPID=1; this image does not. Pass --env VSM_NOPID=1 if your runtime depends on it.

Why no shell or 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 shell for interactive use; runtime images also typically don't include debugging tools. 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 dhi.io/varnish:<tag>

or mount debugging tools with the Image Mount feature:

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

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.

Varnish-specific migration notes

• Docker Official Image: Read Replacing Docker Hub varnish (official image) for entrypoint, env, and port differences before changing image references.
• VCL file permissions: UID 65532 must be able to read mounted default.vcl (for example chmod 644 on the host file).
• /var/lib/varnish: Use a tmpfs or writable volume; example: docker run --tmpfs /var/lib/varnish:exec ….
• Backend TLS in VCL: This image builds varnishdwithout--with-ssl. VCL backend .tls usage will not load. Terminate TLS in front of Varnish or use plain HTTP to the next hop.

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.