Cluster Viewer

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Why Use Cluster Viewer?

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When to Use It

• Confirm the cluster is up — See which members are alive and who the leader is
• Check a link — See whether data-plane links between hosts are connected
• Find who runs an exclusive piece of LoT — Timers, ON START actions, exclusive connectors, and scheduled connector events run on one node
• See partition placement — See which host owns each partition and where the copies sit

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What the Window Shows

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Details

• Node
• Links
• Ownership
• Partitions
• Clients

The selected host: whether it is alive, its role, and its endpoint when the cluster published one.For the host you are connected to, the tab also shows the term and commit index, and whether that host holds the LoT lease.LoT shows the version this host has applied against the version the cluster has committed, whether those match, and any apply errors. Connector listeners lists the server connectors that host reported. Outgoing data-plane links lists the links that start on this host.

Replication on the host you are connected to: connected peers, forward backlog, dropped forwards, quorum failures, and how long the last quorum took.Data-plane links lists every reported link, with its state (connected, connecting, disconnected, or unknown). A stale report is marked stale.

Which host runs each piece of LoT that must run on exactly one node:

Kind	What it is
Actions (timers, ON START)	Scheduled actions, and actions that run once when the cluster session starts
Exclusive connectors	Connectors that hold a device, a serial port, or a server port
Scheduled connector events	A connector’s timed events

Owner is the host that runs it. Next is the host that takes it if the owner is lost. Epoch goes up each time the entity moves. Unowned means no live host can run it, so it runs nowhere until one can. An exclusive connector is defined on every node, but only its owner opens the connection. The others hold it ready.Select a node on the canvas first if you want the list limited to entities that node owns.

The partition map: how many partitions there are, the replication factor, how many are under-replicated, and which host owns each one.Under-replicated partitions still work. Their replica set is smaller than the factor because there are not enough live hosts to place every copy — for example while a host is down. A healthy cluster shows none.Pick a host to highlight the partitions it owns, the ones where it only keeps a copy, and the ones it does not hold.

The MQTT clients connected to each node right now, with a total across the cluster. A client is connected to one node. Behind a load balancer, the node can change each time it reconnects.Under Show the clients of, pick All nodes or one node. Filter by client ID, user, or address, and sort by Last active, Newest connection, Most queued, or Client id. The connections the nodes open to each other are hidden unless you turn on Show the cluster’s own connections.Each card shows the client ID, user, address, MQTT version, messages in and out, and when it was last active. A queued badge counts messages waiting for that client; a number that keeps growing means the client isn’t keeping up. Expand a card for when it connected, its last packet, bytes in and out, and how long the broker keeps its session after it disconnects.Lists refresh every 7 seconds. Other nodes’ clients are relayed by those nodes, so they can be a few seconds older. An older broker reports only the clients of the node you’re connected to.

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Next Steps