Doc: update logging convention
Update the logging convention as capnslog is replaced by zap.
# Logging Conventions
-etcd uses the [capnslog][capnslog] library for logging application output categorized into *levels*. A log message's level is determined according to these conventions:
+etcd uses the [zap][zap] 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
+* 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:
- * A failure to allocate disk space for WAL
+ * 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 normal server's operation.
+ * Examples:
+ * Startup configuration
+ * Start to do 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 raft message to a remote peer
* Failure to receive heartbeat message within the configured election timeout
-* Notice: Normal, but important (uncommon) log information.
+* Error: Data has been lost, a request has failed for a bad reason, or a required resource has been lost.
* Examples:
- * Add a new node into the cluster
- * Add a new user into auth subsystem
+ * Failure to allocate disk space for WAL
-* Info: Normal, working log information, everything is fine, but helpful notices for auditing or common operations.
+* Panic: Unrecoverable or unexpected error situation that requires stopping execution.
* Examples:
- * Startup configuration
- * Start to do snapshot
+ * Failure to create the database
-* Debug: Everything is still fine, but even common operations may be logged, and less helpful but more quantity of notices.
+* Fatal: Unrecoverable or unexpected error situation that requires immediate exit. Mostly used in the test.
* Examples:
- * Send a normal message to a remote peer
- * Write a log entry to disk
+ * Failure to find the data directory
+ * Failure to run a test function
-[capnslog]: https://github.com/coreos/pkg/tree/master/capnslog
+[zap]: https://github.com/uber-go/zap
