Metric amongst loopbacks

I want to track the IGP metric of my loopbacks. I want to automate the task. Initially I am thinking of use some sorts of expect scripts to login the routers and extract the information from the cli output. Then I tried to poll it from snmp MIB values.

However, I have come across some network monitoring tools like ansible and friends here so this task might serve me a learning opportunity for them. It would be great if you could enlighten me with some pointers to start with. Juniper boxes running Junos without upgraded FreeBSD.

Thanks.