We have bought some reserved EC2 instances in different availability zones in eu-west-1 region. When launching a new instance, via API or AWS control panel, we do usually set "No preference" as the availability zone.
In case of we have an "unused" reserved instance in an availability zone, does AWS still prefer that very zone even "No preference" is selected when launching the instance? Or, should we explicitly define the availability zone to match the inactive instance reservation?
I tried to look for the answer from the AWS documentation, but without luck yet: