FakeDNS, to use as dynamic dns for Docker containers

FakeDNS is a fake dynamic DNS server. It allows you to dynamically bind hostnames to clients ip addresses. Originally, it is created to dynamically resolve hostnames inside Docker container, so there are following limitations (in current version):

• It knows only about registred domain names (it means whose names it was told about)
• It requires every client to connect to FakeDNS server to register its domain name, or it won't be resolved by FakeDNS
• Registred IPtoHostname map doesn't survive FakeDNS restart

To use it with Docker you should run server somewhere (for example in separate container like in demo below) and run your Docker containers with the following command line argument

 --dns=<IP_ADDRESS_OF_FAKE_DNS_CONTAINER> --dns=8.8.8.8 --dns=8.8.4.4

You can find details of what this docker run command line argument actually means here.

Important. I'd recommend to add Google DNS as well, 'cause FakeDNS knows only about registred domain names.

To run demo you should checkout this repository and follow instructions you can find here.

Image is based on Alpine 3.5.

Binary version of FakeDNS server is built with GraalVM.

Final image size is about 20 MB.

Run FakeDNS server:

docker run -d --name=fakedns-server silvmike/fakedns-server:latest
echo FAKE DNS IS READY ON $(docker inspect --format '{{ .NetworkSettings.IPAddress }}' fakedns-server)

cd fakedns-server && docker build -t silvmike/fakedns-server .

1. DNS server listens to 53 port on specified host for UDP
2. Registrator listens on specified port

Registrator is an application used to register host with provided hostname.

cd fakedns-server && mvn package && cd ..

The result must be here in the end:

fakedns-server/target/fakedns-server.jar

• java -jar fakedns-server.jar <hostname to listen: localhost, 0.0.0.0, etc.> <registrator port>

Example:

 java -jar fakedns-server.jar localhost 8099

P.S. You can easily check it:

 dig @localhost myfake.host.org

Connects to specified registrator running on specified host and listening to specified port, and registering this host (that running client) with specified hostname.

cd fakedns-client && mvn package && cd ..

The result must be here in the end:

fakedns-client/target/fakedns-client.jar

• java -jar fakedns-client.jar <hostname of registrator> <registrator port> <your fake hostname>

Example:

 java -jar fakedns-client.jar localhost 8099 myfake.host.org

Connects to specified registrator running on specified host and listening to specified port, and registering this host (that running client) with specified hostname.

• sh fakedns-client.sh <hostname of registrator> <registrator port> <your fake hostname>

Example:

 sh fakedns-client.sh localhost 8099 myfake.host.org

P.S. netcat is required.

http://www.zytrax.com/books/dns/ch15/

http://www.freesoft.org/CIE/Topics/78.htm

Microsoft TechNet 'How DNS Works'