When you kill a monolith you kill a random selection of inflight tasks from every part of your application.
So a rare bug in your mailing list signup workflow that hangs the process and causes it to be killed causes a random selection of inflight webpage requests, payment transactions, message handlers and business processes to fail. And if those failures aren’t all cleanly handled, your mailing list signup bug could propagate into a much wider issue.
Whereas if you have a ‘mailing list service’ that has its own processes that can be killed and respawned, that bug only takes our mailing list processing. Which is good because the bug was probably made by the team who owns mailing list processing. And they can roll back their code and be on their way, with nobody else needing to know or care.
So a rare bug in your mailing list signup workflow that hangs the process and causes it to be killed causes a random selection of inflight webpage requests, payment transactions, message handlers and business processes to fail. And if those failures aren’t all cleanly handled, your mailing list signup bug could propagate into a much wider issue.
Whereas if you have a ‘mailing list service’ that has its own processes that can be killed and respawned, that bug only takes our mailing list processing. Which is good because the bug was probably made by the team who owns mailing list processing. And they can roll back their code and be on their way, with nobody else needing to know or care.