I am trying to upgrade my company’s current self-hosted Enterprise Mattermost server from version 5.23 to 9.3
It is running MySQL and I have tried the upgrade previously but upon upgrading it lost all the connections between users and channels and each person that logged in had no channels assigned to them, even the ones they created themselves. It is currently hosted on CentOS8 and I have built a new RHEL9 server with 9.3 that I will migrate the DB over to once the current one is upgraded to the latest version I am running on the RHEL server. Are there specific instructions on how to do this without losing any information or account pointers?
Thanks,
Chris
Does it have to use Postgres? I have a new instance of 9.3 running successfully on MySQL as well.
Short answer: yes. Mattermost v11 will remove all support for MySQL. Might as well get it over with sooner than later!
For your old instance, you probably need to upgrade to 5.37, which is the first ESR release after 5.32. Then 6.3, 7.1, 7.8, 8.1… See Release Lifecycle - Mattermost documentation
Note that in 9.4, support for MySQL 5.7 was dropped in favor of 8 Mattermost changelog - Mattermost documentation
My best guess is you need to get Mattermost upgraded to about 8.1 and then migrate to Postgres. But read though those docs! 
I actually had a new RHEL9 9.3 Mattermost server with Postgres as well and I was hoping I wouldn’t have to migrate from MySQL for sake of ease but I will move forward with upgrading the old and then migrate and transfer to Postgres as you have suggested. Thanks for the help!