AEM Upgrade to AEM 6.5

Adobe documentation captures all the scenarios for the AEM upgrade^[1]. On a high level, the changes are:

1. There are two ways to upgrading the AEM instance, one is in-place upgrade and other is fresh install approach based on AEM content size.
2. Upgrade artifacts by compiling against 6.5 uber jar.
3. Test and fix any issues due to deprecated features/overlaid capabilities change.
4. From 6.4, as part of the sustainable upgrades process, there is a repository restructuring that can be done (not mandatory)^[2].
5. Process on how to roll out the changes to production.

AEM Upgrade flowchat | Credit - Adobe ExperienceLeague

If this is hard, adobe offers a backward compatibility mode from 6.3 with which one can run a 6.3 AEM artifact on a 6.5 instance^[3].

Pattern detector is a mechanism provided by Adobe to easy identification of possible problems that will come up during upgrade by validating against deprecated features and overlays^[4].

AEM 6.5 is compatible with Java 8^[5].

References

1 https://docs.adobe.com/content/help/en/experience-manager-65/deploying/upgrading/upgrade.html
2 https://docs.adobe.com/content/help/en/experience-manager-65/deploying/restructuring/repository-restructuring.html
3 https://docs.adobe.com/content/help/en/experience-manager-65/deploying/upgrading/backward-compatibility.html
4 https://docs.adobe.com/content/help/en/experience-manager-65/deploying/upgrading/pattern-detector.html
5 https://docs.adobe.com/content/help/en/experience-manager-65/deploying/introduction/technical-requirements.html