Using Deployments makes upgrading a straightforward operation. As with any upgrade, you should have good backups in case something goes wrong. Most of the issues you will run into will happen during upgrades. Cloud-native applications are supposed to make dealing with this relatively easier which is possible only if you have a very strong development team that has the ability to do incremental rollouts (with support for rollback).

There is a trade-off between getting features out for customers to see versus spending a lot of time ensuring developer training, automated tests, and disciplined developers and product managers. Remember, most successful companies that do upgrades in production multiple times a day had for years monolithic applications that generated revenue before they were able to switch to a microservices-based approach.

Most methods here work great if you have stateless applications. If you have a state stored anywhere, back up before you try anything.