SSIS while upgrading SQL server I want to upgrade SQL server from 2005 to 2012 (I'm thinking of in-place upgrade).
Today I have several SSIS packages that works with other servers.
The SQL version in those servers is mainly 2005.

My question is what happen to the SSIS when i'm upgrading?

Do i need to upgrade the SSIS as well?

Could the SSIS work without me upgrading it?

Are there any compatibility issues with the integration server? can 2012 work with 2005 (and the opposite - because replication have compatibility problems)

I'm not a big fan of the SSIS so my goal is to touch it as less as i can so it will keep on working.
Unfortunately you need to migrate your 2005 packages to 2012 using Data Tools. Depending on the complexity of each one this task will be more or less complicated. Here some useful links that I have used in the past:

https://devinknightsql.com/2012/05/16/upgrading-packages-to-ssis-2012/

https://sqldusty.com/2012/03/19/upgrade-2008-ssis-packages-to-2012-like-a-boss/

https://blogs.msdn.microsoft.com/mattm/2008/03/22/package-upgrade-wizard/