1. Which must be upgraded first - server or proxies? There is no compatibility matrix of various versions of Zabbix components (e.g. which combinations of server, proxy, agent are supported and which ones are not).
2. Are there any instructions/best practices for upgrading proxies?
3. What are the upgrade paths? E.g. can one go from 2.2 to 3.0 directly or only through 2.4?
4. There is no check-list to determine if the upgrade was successful or if it failed.
5. There is no link to the requirements of the 3.0. That is the first thing that must be checked!