One thing I ve been painfully working on is upgrades as well. We have, in our bank, 2 system, one to trade with exchange automatically, one to approve short sel

One thing I ve been painfully working on is upgrades as well. We have, in our bank, 2 system, one to trade with exchange automatically, one to approve short sells based on various inventories. Both are built as micro services, with various robots talking to each other, optimized at the sub millisecond response time. It works. But the difference is one has a release/repository organization based on each individual service, the other is deployed as a monolith with all robots all redeployed. The system with split releases is barely maintanable, bugs appear in one version of a shared dependencies and we cant upgrade all robots without a mind blowingly complex procedure, regression tests etc. It s sometimes impossible and bugs are worked around up or downstream. The monolithically deployed system is a breeze, we can fix an issue in a dependency and all robots benefit the next week. There's no difference technically except in the minds and cultures of the team that in one system it s too hard to deploy everything and in the other it s mass redeployed every week.