This Python application and Docker image provide an utility that periodically parses the DHCP leases files and updates the bind9 DNS configuration so that hosts that are assigned IP addresses dynamically from DHCP can be looked up via DNS.
There are several keys to making all this work. The utility needs to be able to read the DHCP lease file as well as write a file to a location that can be read by the DNS server; so more than likely this utility should be run on the same host that is running DHCP and DNS. Additionally, this utility needs to be able to run the bind9 utility rndc to reload the DNS zone. This means that it needs a DNSSEC key and secret to access the DNS server.
Lastly, this utility generates a file that can be $include-ed into a bind9 zone file, so the original zone file needs to be augmented with a $INCLUDE statement that includes the files to which the uility is configured to write via the -dest command line option.
To build the docker image use the command:
docker build -t harvester .
To run the utility, a docker command similar to what is below may be used
docker run -d --name=dhcpharvester \
-v `pwd`/key:/key -v /var/lib/maas/dhcp:/dhcp -v /etc/bind/maas:/bind harvester \
-f '^(?!cord)' -u -s 192.168.42.231 -p 954 -k /key/mykey.conf -z cord.lab -r 5m \
-y -t 1s
There is a simple REST API on this utility so that an external client can asynchronously invoke the DHCP harvest behavior. The REST API is synchronous in that the request will not return a response until the harvest is complete. To invoke the request a HTTP PUT request needs be sent to the utility, such as by curl:
curl -XPOST http://<apiserver>:<apiport>/harvest
Currently there is not security around this so it could be abused. There is some protection so that if the system is sent multple request if won't actually reharvest until a quiet period has expired. The purpose is to not allow the system to be overloaded.
Internally the implementation uses threads and queues to communicate between the threads when the utility is in the mode to periodically harvest.
For the verification of IP addresses, i.e. pinging the hosts, worker threads are used to support concurrency, thus making the verification process faster.