Requests on a reporting server took ten seconds every morning while CPU sat mostly idle. iowait at 60% pointed at storage; iostat and pidstat pointed at logrotate compressing a 40 GB log on the same volume as the database. How we found it and moved the work off the hot path.
We moved all EBS volumes from gp2 to gp3 to save 20 percent, as every cost guide recommends. Two days later, nightly reports on our self-managed Postgres took twice as long. The 2 TB gp2 volume had 6,000 IOPS and 250 MiB/s; gp3 defaults are 3,000 and 125. Provisioning both fixed it.
EBS storage kept rising while our clusters stayed the same size. Preview environments created PersistentVolumes with a Retain policy, deleted namespaces left the volumes behind, and a snapshot job never expired anything. We found, verified and deleted 612 volumes and 9,400 snapshots.