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Unbound DNS Server Docker Image

Supported tags and respective Dockerfile links

What is Unbound?

Unbound is a validating, recursive, and caching DNS resolver.

unbound.net

How to use this image

Standard usage

Run this container with the following command:

docker run --name my-unbound -d -p 53:53/udp -p 53:53/tcp \
--restart=always mvance/unbound:latest

For a DNS server with lots of short-lived connections, you may wish to consider adding --net=host to the run command for performance reasons. However, it is not required and some shared container hosting services may not allow it. You should also be aware --net=host can be a security risk in some situations. The Center for Internet Security Docker 1.6 Benchmark recommends against this mode since it essentially tells Docker to not containerize the container's networking, thereby giving it full access to the host machine's network interfaces. It also mentions this option could cause the container to do unexpected things such as shutting down the Docker host as referenced in Docker Issue #6401 . For the most secure deployment, unrelated services with confidential data should not be run on the same host or VPS. In such cases, using --net=host should have limited impact on security.

Serve Custom DNS Records for Local Network

While Unbound is not a full authoritative name server, it supports resolving custom entries on a small, private LAN. In other words, you can use Unbound to resolve fake names such as your-computer.local within your LAN.

To support such custom entries using this image, you need to provide an a-records.conf or srv-records.conf file. This conf file is where you will define your custom entries for forward and reverse resolution.

A records

The a-records.conf file should use the following format:

# A Record
  #local-data: "somecomputer.local. A 192.168.1.1"
  local-data: "laptop.local. A 192.168.1.2"

# PTR Record
  #local-data-ptr: "192.168.1.1 somecomputer.local."
  local-data-ptr: "192.168.1.2 laptop.local."

Once the file has your entries in it, mount your version of the file as a volume when starting the container:

docker run --name my-unbound -d \
-p 53:53/udp -p 53:53/tcp \
-v $(pwd)/a-records.conf:/opt/unbound/etc/unbound/a-records.conf:ro \
--restart=always mvance/unbound:latest

SRV records

The srv-records.conf file should use the following format:

# SRV records
# _service._proto.name. | TTL | class | SRV | priority | weight | port | target.
_etcd-server-ssl._tcp.domain.local.  86400 IN    SRV 0        10     2380 etcd-0.domain.local.
_etcd-server-ssl._tcp.domain.local.  86400 IN    SRV 0        10     2380 etcd-1.domain.local.
_etcd-server-ssl._tcp.domain.local.  86400 IN    SRV 0        10     2380 etcd-2.domain.local.

Run a container taht use this SRV config file:

docker run --name my-unbound -d \
-p 53:53/udp -p 53:53/tcp \
-v $(pwd)/srv-records.conf:/opt/unbound/etc/unbound/srv-records.conf:ro \
--restart=always mvance/unbound:latest

Override default forward

By default, forwarders are configured to use Cloudflare and CleanBrowsing DNS. You can retrieve the configuration in the 1.10.0/forward-records.conf file.

You can create your own configuration file and override the one placed in /opt/unbound/etc/unbound/forward-records.conf in the container.

Example forward-records.conf:

forward-zone:
  # Forward all queries (except those in cache and local zone) to
  # upstream recursive servers
  name: "."

  # my DNS
  forward-addr: 192.168.0.1@53#home.local

Once the file has your entries in it, mount your version of the file as a volume when starting the container:

docker run --name my-unbound -d -p 53:53/udp -p 53:53/tcp -v \
$(pwd)/forward-records.conf:/opt/unbound/etc/unbound/forward-records.conf:ro \
--restart=always mvance/unbound:latest

Use a customized Unbound configuration

Instead of using this image's default configuration for Unbound, you may supply your own configuration. If your customized configuration is located at /my-directory/unbound/unbound.conf, pass /my-directory/unbound as a volume when creating your container:

docker run --name=my-unbound \
--volume=/my-directory/unbound:/opt/unbound/etc/unbound/ \
--publish=53:53/tcp \
--publish=53:53/udp \
--restart=unless-stopped \
--detach=true \
mvance/unbound:latest

This will expose all files in /my-directory/unbound/ to the container. As an alternate way to serve custom DNS records for any local zones, either place them directly in your unbound.conf, or place the local zones in a separate file and use Unbound's include directive within your unbound.conf:

include: /opt/unbound/etc/unbound/local-zone-unbound.conf

Your volume's contents might eventually look something like this:

/my-directory/unbound/
-- unbound.conf
-- local-zone-unbound.conf
-- secret-zone.conf
-- some-other.conf

Overall, this approach is very similar to the a-records.conf approach described above. However, by passing your unbound directory rather than a single file, you have more options for customizing and segmenting your Unbound configuration.

Note: Care has been taken in the image's default configuration to enable security options so it is recommended to use it as a guide.

User feedback

Documentation

Documentation for this image is stored right here in the README.md.

Documentation for Unbound is available on the project's website.

Issues

If you have any problems with or questions about this image, please contact me through a GitHub issue.

Contributing

You are invited to contribute new features, fixes, or updates, large or small. I imagine the upstream projects would be equally pleased to receive your contributions.

Please familiarize yourself with the repository's README.md file before attempting a pull request.

Before you start to code, I recommend discussing your plans through a GitHub issue, especially for more ambitious contributions. This gives other contributors a chance to point you in the right direction, give you feedback on your design, and help you find out if someone else is working on the same thing.

Acknowledgments

The code in this image is heavily influenced by DNSCrypt server Docker image, though the upstream projects most certainly also deserve credit for making this all possible.

Licenses

License

Unless otherwise specified, all code is released under the MIT License (MIT). See the repository's LICENSE file for details.

Licenses for other components