Amazon EC2 instance ubuntu upgrade from 16 to 18

We have received this email recently from Amazon AWS:

Your account has been identified as having started an instance or continuing to run instances of Ubuntu 16.04 over the last 6 months.

Canonical, the company behind Ubuntu, announced that the Ubuntu 16.04 LTS (Long Term Support) period will end on Friday, April 30, 2021 [1].

Canonical offers ESM for Ubuntu 16.04 LTS, which guarantees an additional three years of security patches. ESM is included with Ubuntu Pro 16.04 instances, or free Ubuntu instances with an attached Ubuntu Advantage subscription[2][3].

All Ubuntu 16.04 LTS users are encouraged to upgrade to Ubuntu 18.04 LTS or Ubuntu 20.04 LTS.

I'm new to AWS and EC2. We have some EC2 instances running in which Ubuntu is 16.04 LTS and our application/flask, db, and some other services are already running. Even when I restart my EC2 instance, these services automatically run in the background on restarting.

If I upgrade to Ubuntu 18.04, will all my background services, flask server, my open ports, etc. be running the same as before or will I need to do my whole setup again? As I don't know what services are running and how is it running. Will the upgrade of Ubuntu from 16.04 to 18.04 be similar to restarting an instance or more than that?

Thanks in advance!

You need to test this yourself. Nobody else than you know the exact structure of your setup.

Knowing all components of the setup is the minimum required information to make an educated guess if upgrade can be done without additional work.

However, even if the complete setup is known, one cannot know for sure. So, the only possibility is to test the upgrade and test everything on upgraded system.

I also recommend you to target Ubuntu 20.04 LTS, that way you don't need to worry about Ubuntu 18.04 LTS support ending.