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 wbitt-network-multitool image

This Docker Hardened wbitt-network-multitool image includes:

• nginx - Minimal web server for serving test content and providing HTTP/HTTPS endpoints
• curl - HTTP client for testing endpoints
• wget - Non-interactive network downloader
• dig - DNS lookup utility (from bind-tools)
• nslookup - Legacy DNS lookup utility
• ping - ICMP echo utility for connectivity tests
• traceroute - Network path tracing tool
• mtr - Combines ping and traceroute for diagnostics
• tcpdump - Packet capture tool
• netstat - Network connections and listening ports (net-tools)
• ip - iproute2 utilities for interface and route management
• jq - JSON processor for API responses

The -extra variant includes additional tools for advanced networking, database connectivity, and security testing:

• apache2-utils - Apache HTTP server benchmarking tools (ab, htpasswd)
• ethtool - Ethernet device configuration and diagnostics
• git - Version control system
• iperf3 - Network performance measurement and tuning tool
• lftp - Sophisticated FTP/HTTP client
• mysql-client - MySQL database client for connectivity testing
• netcat-openbsd - TCP/IP swiss army knife for port scanning and data transfer
• net-snmp-tools - SNMP tools for network management
• nmap - Network exploration and security auditing tool
• nmap-scripts - Nmap scripting engine scripts for advanced scanning
• postgresql-client - PostgreSQL database client for connectivity testing
• samba-client - SMB/CIFS client tools for Windows file sharing
• socat - Multipurpose relay tool for bidirectional data transfer
• tshark - Network protocol analyzer (Wireshark CLI)

Start a wbitt-network-multitool image

Basic usage

Run the following command to start a wbitt-network-multitool container with the default nginx web server:

$ docker run -d --name wbitt-network-multitool -p 80:80 -p 443:443 \
  dhi.io/wbitt-network-multitool:<tag>

This starts the container with nginx listening on ports 80 (HTTP) and 443 (HTTPS).

Interactive shell access

To get an interactive shell and use the networking tools:

$ docker run --rm -it dhi.io/wbitt-network-multitool:<tag>-dev /bin/sh

Note: Use the -dev variant for interactive shell access, as runtime variants don't include a shell.

With Docker Compose

version: '3.8'
services:
  network-multitool:
    image: dhi.io/wbitt-network-multitool:<tag>
    container_name: wbitt-network-multitool
    ports:
      - "80:80"
      - "443:443"
    environment:
      - HTTP_PORT=80
      - HTTPS_PORT=443

Environment variables

Example with custom ports:

$ docker run -d --name wbitt-network-multitool \
  -e HTTP_PORT=8080 \
  -e HTTPS_PORT=8443 \
  -p 8080:8080 \
  -p 8443:8443 \
  dhi.io/wbitt-network-multitool:<tag>

Common wbitt-network-multitool use cases

Network troubleshooting in Kubernetes

Deploy as a pod for network troubleshooting:

apiVersion: v1
kind: Pod
metadata:
  name: wbitt-network-multitool
spec:
  containers:
  - name: wbitt-network-multitool
    image: dhi.io/wbitt-network-multitool:<tag>
    ports:
    - containerPort: 80
    - containerPort: 443

Or run directly with kubectl:

$ kubectl run wbitt-network-multitool --image=dhi.io/wbitt-network-multitool:<tag>

DNS resolution testing

Test DNS resolution from within a running container:

$ docker exec -it wbitt-network-multitool dig google.com
$ docker exec -it wbitt-network-multitool nslookup google.com

Network connectivity testing

Test network connectivity and HTTP endpoints:

$ docker exec -it wbitt-network-multitool ping -c 4 8.8.8.8
$ docker exec -it wbitt-network-multitool curl -I https://www.google.com

Network path tracing

Trace the network path to a destination:

$ docker exec -it wbitt-network-multitool mtr -c 10 google.com

Note: mtr works without elevated privileges. For traceroute, see the "Tools requiring privileged mode" section below.

Packet capture

Note: tcpdump requires privileged mode. See the "Tools requiring privileged mode" section below for usage.

Port scanning and checking

Check open ports and network connections:

$ docker exec -it wbitt-network-multitool netstat -tulpn

Custom web content

Mount your own HTML content to replace the default index page:

$ docker run -d --name wbitt-network-multitool \
  -v /path/to/html:/usr/share/nginx/html:ro \
  -p 80:80 \
  dhi.io/wbitt-network-multitool:<tag>

Using the extra variant for advanced testing

For database connectivity testing, security scanning, or advanced networking:

$ docker run --rm -it dhi.io/wbitt-network-multitool:<tag>-extra-dev /bin/sh

Inside the container, you can use tools like:

# Database connectivity
$ mysql -h database-host -u user -p
$ psql -h database-host -U user

# Network performance testing
$ iperf3 -c server-host

# Security scanning
$ nmap -sV target-host

# Protocol analysis
$ tshark -i eth0

Tools requiring privileged mode

Some network diagnostic tools require elevated privileges to access raw network sockets. These tools need --privileged mode when using the -dev variant (which runs as root).

Traceroute:

$ docker run --rm --privileged \
  dhi.io/wbitt-network-multitool:<tag>-dev /bin/sh -c "traceroute google.com"

Packet capture (tcpdump):

$ docker run --rm --privileged \
  dhi.io/wbitt-network-multitool:<tag>-dev /bin/sh -c "tcpdump -i any -c 10 icmp"

Or with a running container:

$ docker run -d --name wbitt-network-multitool --privileged \
  dhi.io/wbitt-network-multitool:<tag>-dev sleep 3600
$ docker exec -it wbitt-network-multitool tcpdump -i any -c 10

Note: The -dev variant runs as root user, which provides the necessary permissions for these diagnostic tools when combined with --privileged mode.

Notes and limitations

• Runtime variants run as non-root user (nginx, UID 65532) for enhanced security
• Dev variants run as root user to allow package installation and system modifications
• The nginx process itself runs as the nginx user (UID 65532) in all variants for security
• Self-signed SSL certificates are automatically generated at /certs/server.crt and /certs/server.key
• Access and error logs are forwarded to stdout/stderr for container log collection
• The web root is at /usr/share/nginx/html/
• The container includes a built-in health check that verifies nginx is responding on the HTTP port
• For interactive shell access and running commands, use the -dev variant
• Tools like traceroute and tcpdump require --privileged mode to access raw network sockets

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.