Do I have to update the Jira Core from 8.6.1 to 8.11.0 if I have:
I see you've been through this process before, as you posted a similar question last year.
The good news is that the process is roughly the same, although in this case you can jump directly from 8.6 to 8.11 whereas in the last upgrade, you might have had to do an additional upgrade to get some required upgrade steps. Those aren't a problem anymore, so you can go directly to your desired version.
1 - If you're upgrading both Jira Core/Software and Jira Service Desk, upgrade Jira Core/Software only. You'll later upgrade Service Desk directly in Jira, without a separate installer.
2 - Upgrade JIRA Core/Software first, and then JIRA Service Desk
3 (Maybe at first install Jira and update it to the last version and then install ServiceDesk?) - Yes, that's the correct approach as described in the previous steps
4 - Always generate a backup from your current JIRA version before upgrading it. In case your upgrade may fail, you can roll-up to the previous version.
You can check more details of the steps in the documentation below:
There's no special requirements. The upgrade doc for Core covers everything, and the upgrade process is done in-place - you won't lose any data.
Of course, before upgrading production, you should
But the upgrade should be straightforward for you on these versions.
I also think the key for a successful upgrade is testing in a staging environment.
You should check if your application database is supported in 8.11, it seems that some databases are no longer supported in 8.11 when I compared with 8.6 supported platform:
If you are using one of these databases you will need to consider upgrade it prior the upgrade.