Sets the retention of the specified log group. With a retention policy, you can configure the number of days for which to retain log events in the specified log group.
CloudWatch Logs doesn’t immediately delete log events when they reach their retention setting. It typically takes up to 72 hours after that before log events are deleted, but in rare situations might take longer.
To illustrate, imagine that you change a log group to have a longer retention setting when it contains log events that are past the expiration date, but haven’t been deleted. Those log events will take up to 72 hours to be deleted after the new retention date is reached. To make sure that log data is deleted permanently, keep a log group at its lower retention setting until 72 hours after the previous retention period ends. Alternatively, wait to change the retention setting until you confirm that the earlier log events are deleted.
When log events reach their retention setting they are marked for deletion. After they are marked for deletion, they do not add to your archival storage costs anymore, even if they are not actually deleted until later. These log events marked for deletion are also not included when you use an API to retrieve the storedBytes value to see how many bytes a log group is storing.