If you want to do logs, you can use graylog or kibana, both using elasticsearch for storage. This allows to find what was connecting where at some point in time (HTTP request logs and database connection logs).
If you want to graph connections from service to service in real time. I've actually never found anything that was capable of doing that, not even paid software.
If you want to graph connections from service to service in real time. I've actually never found anything that was capable of doing that, not even paid software.