Logging conventions

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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

Logging conventions