How do I preserve an approval in Gerrit with new patchset - gerrit

Question

I'm setting up a Gerrit server for the team. I've used Gerrit in the past, but I've never set one up.
One feature I know I've used in the past is, once I get a CL approved, I can rebase the branch without losing the approval. I assume this is a setting somewhere, but I can't find it.

Answer 1

You need to set the "Submit Type" of the repository (in the repository configuration page) to one of these:
Rebase If Necessary
If the change being submitted is a strict superset of the destination branch, then the branch is fast-forwarded to the change. If not, then the change is automatically rebased and then the branch is fast-forwarded to the change.
When Gerrit tries to do a merge, by default the merge will only succeed if there is no path conflict. A path conflict occurs when the same file has also been changed on the other side of the merge.
Rebase Always
Basically, the same as Rebase If Necessary, but it creates a new patchset even if fast forward is possible AND like Cherry Pick it ensures footers such as Change-Id, Reviewed-On, and others are present in resulting commit that is merged.
Thus, Rebase Always can be considered similar to Cherry Pick, but with the important distinction that Rebase Always does not ignore dependencies.
See more details in the Gerrit documentation here.

Answer 2

I think you are looking for the Copy All Score On Trivial Rebase labels.
The example below is from our project.config. For the Verified label the scores will be copied if there is a Trivial Rebase or a No Code Change patchset added, the No Code Change basically means an updated commit message.
[label "Verified"]
function = MaxWithBlock
value = -1 Fails
value = 0 No score
value = +1 Verified
copyAllScoresIfNoCodeChange = true
copyAllScoresOnTrivialRebase = true
defaultValue = 0