Amazon S3 - How to transition 1 backup file to Glacier per month
You have to move that monthly backup to some prefix say in the same bucket and set up a rule to move this monthly backup to glacier.
Probably if you are sound with python/java/nodejs , you can create a lambda function and schedule it on a monthly basis (say 1st of every month).This lambda function will move your latest backup of the month to the prefix and according to the rule you create for glacier storage ,it will be automatically gets transitioned to Glacier.
Unless I am missing something , here is blog to setup a policy to transfer s3 data to glacier.
Archiving Amazon S3 Data to Glacier
P.S : Moving an s3 object includes 2 steps-
1. copy object from source to destination (s3 bucket monthly-prefix) 2. delete original object