> ## Documentation Index > Fetch the complete documentation index at: https://docs.coreflux.org/llms.txt > Use this file to discover all available pages before exploring further. # Cluster Viewer > See the nodes, leader, links, LoT ownership, and partitions of a Coreflux cluster from the broker host you are connected to ## Why Use Cluster Viewer? A cluster is several broker hosts acting as one system. Cluster Viewer draws that system from the broker host you are already connected to, so you can see who leads, which links are up, which node owns each exclusive piece of LoT, and how partitions are placed — without opening a shell on every host. > [!NOTE] > > Cluster Viewer carries a **Beta** badge on its window. The dock icon is labeled **Cluster**. It appears only while the connected broker host is publishing cluster status. > [!TIP] > > **Like a seating chart that updates itself.** You see who is leading, who is sitting in, and who is holding each shared task — from the one host you opened. ## 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 Clustering is an Enterprise license feature. If the license does not grant it, the broker runs standalone and this icon stays off the dock. See [High-availability clustering](/latest/mqtt-broker/clustering) and [Licensing](/latest/mqtt-broker/licensing). *** Open **Cluster** on the dock. The window is read-only. It reads the cluster status the connected broker host publishes. It does not elect a leader, move ownership, or change cluster settings. If clustering is off, the icon is not on the dock. Opening the window another way shows that the connected broker is not publishing cluster status. ## What the Window Shows A strip across the top summarizes the cluster as this broker host sees it: | Item | What it tells you | | - | - | | **Cluster** | The cluster identity | | **Leader** | The host that currently leads | | **Members** | How many members are alive out of the member count | | **Term** / **Commit** | How far leader election and the committed log have progressed | | **LoT** | Whether nodes are on the same committed LoT version, or the versions are mixed | | **Data plane** | How many links between hosts are up | | **Listeners** | Whether any server-connector listener on a member has failed | The strip also says the view is **Live** (or how old the status is), which host you are seeing it from, and that it is **read-only**. The canvas draws each member and the links between them. Select a node to open it on the **Node** tab. Select a link to see each direction. The leader is marked on its node. A host the status names but does not describe yet is drawn as unidentified. > [!WARNING] > > The picture is the view from the broker host you are connected to. It is not a second login to every member. ## Details **Node** 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. ![Coreflux HUB Cluster Viewer window with the Node tab selected: the cluster summary strip across the top, the cluster members and links on the canvas, and the node details panel](https://mintcdn.com/coreflux/9PekAdlvyyrySLnc/images/cluster-viewer/hub-cluster-viewer-node-light.png?fit=max\&auto=format\&n=9PekAdlvyyrySLnc\&q=85\&s=3304d205524e2aaa61ab65c8148a1547) **Links** **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. ![Coreflux HUB Cluster Viewer window with the Links tab selected: the cluster summary strip across the top, the cluster members and links on the canvas, and the links details panel](https://mintcdn.com/coreflux/9PekAdlvyyrySLnc/images/cluster-viewer/hub-cluster-viewer-links-light.png?fit=max\&auto=format\&n=9PekAdlvyyrySLnc\&q=85\&s=b6c4bc1d5c2b32904f7410f31fd3fc97) **Ownership** 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. ![Coreflux HUB Cluster Viewer window with the Ownership tab selected: the cluster summary strip across the top, the cluster members and links on the canvas, and the ownership details panel](https://mintcdn.com/coreflux/9PekAdlvyyrySLnc/images/cluster-viewer/hub-cluster-viewer-ownership-light.png?fit=max\&auto=format\&n=9PekAdlvyyrySLnc\&q=85\&s=3098b8f9b250f96a0bc10111f13db364) **Partitions** 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. ![Coreflux HUB Cluster Viewer window with the Partitions tab selected: the cluster summary strip across the top, the cluster members and links on the canvas, and the partitions details panel](https://mintcdn.com/coreflux/9PekAdlvyyrySLnc/images/cluster-viewer/hub-cluster-viewer-partitions-light.png?fit=max\&auto=format\&n=9PekAdlvyyrySLnc\&q=85\&s=08e8a96be261df65232867e5e2f0b2a9) **Clients** 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. ![Coreflux HUB Cluster Viewer for cluster acme-plant, leader acme-mqtt-2, 3/3 members alive. The Clients tab shows 9 clients (+12 cluster connections) and 0 queued messages, the node filters All nodes, acme-mqtt-1 4, acme-mqtt-2 3, and acme-mqtt-3 2, the filter box, the Last active sort, and the Show the cluster's own connections checkbox, above cards for hmi-panel-03, the HUB's own connection, line1-plc-gw, and energy-meter-gw, each with node, user, address, MQTT version, messages in and out, and last activity](https://mintcdn.com/coreflux/9PekAdlvyyrySLnc/images/cluster-viewer/hub-cluster-viewer-clients-light.png?fit=max\&auto=format\&n=9PekAdlvyyrySLnc\&q=85\&s=c447f955d698db7e81dfa195823d229a) An older broker host may publish only part of this view. The window then names what is missing and still shows the status it did receive. *** ## Next Steps > **[High-Availability Clustering](/latest/mqtt-broker/clustering)** > > Turn clustering on, choose discovery, and read what failover does and does not cover. > **[Connections Manager](/hub/connections)** > > Open the broker host whose cluster status this window reads. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.