etcd/Documentation/contributor-guide/logging.md

Logging Conventions

etcd uses the zap library for logging application output categorized into levels. A log message's level is determined according to these conventions:

• Debug: Everything is still fine, but even common operations may be logged, and less helpful but more quantity of notices. Usually not used in production.

  • Examples:
    • Send a normal message to a remote peer
    • Write a log entry to disk

• Info: Normal, working log information, everything is fine, but helpful notices for auditing or common operations. Should rather not be logged more frequently than once per a few seconds in a normal server's operation.

  • Examples:
    • Startup configuration
    • Start to do a snapshot

• Warning: (Hopefully) Temporary conditions that may cause errors, but may work fine. A replica disappearing (that may reconnect) is a warning.

  • Examples:
    • Failure to send a raft message to a remote peer
    • Failure to receive heartbeat message within the configured election timeout

• Error: Data has been lost, a request has failed for a bad reason, or a required resource has been lost.

  • Examples:
    • Failure to allocate disk space for WAL

• Panic: Unrecoverable or unexpected error situation that requires stopping execution.

  • Examples:
    • Failure to create the database

• Fatal: Unrecoverable or unexpected error situation that requires immediate exit. Mostly used in the test.

  • Examples:
    • Failure to find the data directory
    • Failure to run a test function