Small Changes First
The first few points of this series are going to be around moderately small changes for the greatest gain.
It's easy to recommend the complete overhaul and re-engineering of a system using all the latest and greatest technologies and platforms available, but for many organisations, especially if you're having to maintain and slowly migrate a monolith to something more granular, that kind of change takes many months (and longer) to achieve once you factor in costs (both in time and dollars), training, testing, competing business priorities, etc...
As I run out of quick wins, I'll get into more architectural changes because they're pretty much inevitable as a system grows.
Be Persistent
If a single process is making multiple network calls to the same service, it makes sense that maintaining a persistent connection instead of creating a new connection for each individual call will lead to a performance gain; it reduces the number of connect() syscalls, the number of TLS handshakes and any sort of authentication/authorisation that happens once a connection is established.
See:
The question then becomes: can the endpoint you're connecting to (if you control it) handle the number of persistent connections you'll have open in the worst case?
