Apache ZooKeeper¶

The zookeeper probe monitors an Apache ZooKeeper node via the mntr four-letter command over raw TCP, reporting request latency, packet counts, connection counts, znode and watch counts, file descriptor usage and ensemble state (leader/follower/observer).

Quick start¶

# probes.d/10-zookeeper.yaml — each file under probes.d/ is a YAML array of probes
- name: zookeeper
  type: zookeeper
  params:
    host: localhost
    port: 2181

Parameters¶

Parameter	Must set	Default	Description
`host`	In practice	`localhost`	Node hostname or address
`port`	In practice	`2181`	Client port the four-letter commands are sent to
`timeout`	No	`10`	Connection and command timeout in seconds
`interval`	No	`30`	Seconds between collections
`instance_name`	No	-	Stable identity of this node instead of host:port

Metrics¶

Metric	Unit	Description
`senhub.zookeeper.up`	1	1 when the node answered the `mntr` command
`zookeeper.latency.avg`	s	Average request processing latency (`zk_avg_latency`)
`zookeeper.latency.max`	s	Maximum request processing latency
`zookeeper.connections`	{connection}	Current client connections
`zookeeper.packets.received`	{packet}	Packets received since start
`zookeeper.packets.sent`	{packet}	Packets sent since start
`zookeeper.znodes`	{znode}	Number of znodes in the data tree
`zookeeper.watches`	{watch}	Number of active watches
`zookeeper.file_descriptors.open`	{fd}	Open file descriptors
`zookeeper.synced_followers`	#	Followers in sync with the leader (leader only)
`zookeeper.pending_syncs`	{sync}	Pending sync operations (leader only)

Operational notes¶

The mntr four-letter command must be enabled in zoo.cfg: 4lw.commands.whitelist=mntr (required since ZooKeeper 3.5).
Leader-only metrics (leader_elections, pending_syncs) are only emitted by the ensemble leader; follower nodes emit zero or omit them.
For multi-node ensembles, configure one probe instance per node to monitor the ensemble comprehensively.

Metric reference¶

Every metric this probe can emit. Metric is the OpenTelemetry name the OTLP, Prometheus and Zabbix outputs derive theirs from. Name is what a Nagios check and the API metrics= filter match. PRTG channel is the label PRTG shows, placeholders filled from the series' tags.

Metric	Name	PRTG channel	Unit	Description
`senhub.zookeeper.up`	`senhub.zookeeper.up`	ZooKeeper Up	#	1 when the ZooKeeper node answered the mntr command, 0 otherwise
`zookeeper.latency.avg`	`zookeeper.latency.avg`	ZooKeeper Avg Request Latency	ms	Average request processing latency in milliseconds (zk_avg_latency)
`zookeeper.latency.max`	`zookeeper.latency.max`	ZooKeeper Max Request Latency	ms	Maximum request processing latency in milliseconds (zk_max_latency)
`zookeeper.latency.min`	`zookeeper.latency.min`	ZooKeeper Min Request Latency	ms	Minimum request processing latency in milliseconds (zk_min_latency)
`zookeeper.packets.received`	`zookeeper.packets.received`	ZooKeeper Packets Received	#	Total packets received (zk_packets_received)
`zookeeper.packets.sent`	`zookeeper.packets.sent`	ZooKeeper Packets Sent	#	Total packets sent (zk_packets_sent)
`zookeeper.connections`	`zookeeper.connections`	ZooKeeper Alive Connections	#	Number of active client connections (zk_num_alive_connections)
`zookeeper.outstanding_requests`	`zookeeper.outstanding_requests`	ZooKeeper Outstanding Requests	#	Number of queued requests waiting to be processed (zk_outstanding_requests)
`zookeeper.znodes`	`zookeeper.znodes`	ZooKeeper ZNode Count	#	Total number of znodes in the data tree (zk_znode_count)
`zookeeper.watches`	`zookeeper.watches`	ZooKeeper Watch Count	#	Total number of active watches (zk_watch_count)
`zookeeper.ephemerals`	`zookeeper.ephemerals`	ZooKeeper Ephemeral Nodes	#	Number of ephemeral znodes (zk_ephemerals_count)
`zookeeper.data_size`	`zookeeper.data_size`	ZooKeeper Data Size	B	Approximate size of all znode data in bytes (zk_approximate_data_size)
`zookeeper.file_descriptors.open`	`zookeeper.file_descriptors.open`	ZooKeeper Open File Descriptors	#	Number of open file descriptors (zk_open_file_descriptor_count)
`zookeeper.file_descriptors.max`	`zookeeper.file_descriptors.max`	ZooKeeper Max File Descriptors	#	Maximum allowed file descriptors (zk_max_file_descriptor_count)
`zookeeper.followers`	`zookeeper.followers`	ZooKeeper Followers	#	Number of followers in the ensemble — leader only (zk_followers)
`zookeeper.synced_followers`	`zookeeper.synced_followers`	ZooKeeper Synced Followers	#	Number of followers in sync with the leader — leader only (zk_synced_followers)
`zookeeper.pending_syncs`	`zookeeper.pending_syncs`	ZooKeeper Pending Syncs	#	Number of pending sync operations — leader only (zk_pending_syncs)
`zookeeper.server_state`	`zookeeper.server_state`	ZooKeeper Server Role	#	Always 1; the 'state' attribute carries the role: leader, follower, or standalone