How to update the cloud service?

Question

MongoDB

In the process of project development, a logical need arose to update the cloud service. But so far, the circuit looks rather heavy in view of the fact that it is necessary to update all components without stopping and with a minimum performance landing.
In general, the update process in general terms implies an iterative update, but the main difficulty is that the metadata in the database is the same for all servers. Thus, it turns out that all services, both old (before the update) and new (after the update), must be able to work correctly with both new and old objects in the database.
Maybe there are some best practices and templates for such an update, or some of the users have already faced a similar task, then I will be grateful if you share your solution experience.

Answer 1

rolling out code rarely takes 1 hour,
and warning users that the service will not be available for 1 hour is not a problem

Answer 2

In such cases, there are usually 2 options (of course, you are experienced people, you live on a dozen servers, you have no problems with the database master, there are no statefull fronts, and so on).
1) we make such an update (intermediate), which can work with both base schemas.
2) deploy the second mysql (for example), write an interlayer that in realtime transfers data from the old database to the new one. After updating all the components, we cut down the old base. As an option - to teach the old project to write to the new database.