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

  • Examples:
    • A failure to allocate disk space for WAL

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

• Notice: Normal, but important (uncommon) log information.

  • Examples:
    • Add a new node into the cluster
    • Add a new user into auth subsystem

• Info: Normal, working log information, everything is fine, but helpful notices for auditing or common operations.

  • Examples:
    • Startup configuration
    • Start to do snapshot

• Debug: Everything is still fine, but even common operations may be logged, and less helpful but more quantity of notices.

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