Retaining at least one successful build in Bamboo In Jenkins, you could configure the system to retain a certain number of either successful or failed builds.

With Bamboo, it seems like you can just retain a certain number of builds which rotates the last successful build after 10 failed builds out of the system.

Is there a way in Bamboo to retain the last successful build for an unlimited time?

UPD wait, but is that true with the 10 builds limitation, really?
I have just realized that I could click the UI through the whole build history, both successful and unsuccessful builds.
http://imgur.com/a/JnJ9v
IMHO if your successful build doesn't push to an artifact repository, there's a problem in your pipeline.

Jenkins or Bamboo do not aim at keeping built artifacts forever and they don't give you any versioning delivery, as such that's a point of failure in your delivery system. 

I'd advise to review your method to use an artifact repository and that will solve this XY problem of keeping a successful build inside the build system used as an artefact source.

Note: I can't speak for Bamboo's team, but adding this capacity involves raising the code complexity for a 'side usage'. As such it can makes sense Bamboo's team avoid it to avoid adding code complexity for a feature not in their overall goal. I don't think they avoid it to enforce a best practice, but more to avoid raising unnecessary (from the product point of view) complexity to their code base.