etcd uses the capnslog library for logging application output categorized into levels. A log message's level is determined according to these conventions:
Error: Data has been lost, a request has failed for a bad reason, or a required resource has been lost
Warning: (Hopefully) Temporary conditions that may cause errors, but may work fine. A replica disappearing (that may reconnect) is a warning.
Notice: Normal, but important (uncommon) log information.
Info: Normal, working log information, everything is fine, but helpful notices for auditing or common operations.
Debug: Everything is still fine, but even common operations may be logged, and less helpful but more quantity of notices.