A downside of pulling in rocksdb is that it is a pretty big
C++ library and musl/alpine don't really get on with it.
Switch to using the latest ubuntu LTS image as our base.
This commit adds in an http listener that provides a `/metrics`
endpoint that can be configured as a target by prometheus to
scrape and record metrics.
You may also curl it for yourself.
While playing around with this, I found and fixed a deadlock
in the case that the initial spool in logic found and expired
a message; it would reuse a helper function that wanted to acquire
a lock, but it already held the lock.
Wez Furlong
Mike Hillyer
Cloud User