Re: [Unity-idm-discuss] Question regarding redundant installations

[Krzysztof B. <kb...@un...>]

Hi Laura,

W dniu 17.09.2025 o 11:09, Laura Hofer pisze:
> Hi Krzysztof, Hi Roman,
>
> we are currently planning to switch our Unity setup to an HA setup 
> with one master and two workers.
> This raised the question of how best to proceed with Unity updates: Do 
> all Unity instances have to be stopped and updated at the same time, 
> or can the instances be updated gradually (e.g. within a few hours)? 
> Could the second option cause problems with the database if, for 
> example, the master is already running a newer version of Unity, but 
> the workers are still running an older version? 


Newer Unity can not work on older DB - actually at the startup it will 
try to update DB schema.

That said, if you want to have close-to-zero downtime deployment 
blue-green sounds as the proper approach.

0. Blue is running old version (and can have HA, e.g. 3 instance)

1. install the new version on Green

2. (critical; see notes below) stop Blue, clone DB from Blue to Green

3. start the stack on Green

4. switch routing to Green

5. deprovision Blue


In this scheme #2 is critical, this is when your downtime starts (ends 
at #4). Typically such short downtime is OK: that should take few 
minutes, and in case of troubles with new installation rollback is 
immediate - you just start Blue again.

But we can do better here: instead of fully stopping Unity, we can have 
a feature to put it into RO mode. This would require some development 
and precise definition (note: in Unity even a simple new sign-in is a 
write operation from DB standpoint), but could help a lot: e.g. existing 
sessions/tokens could be serviced w/o interruptions. But that would 
require a new feature.

HTH,
Krzysztof