You are currently browsing legacy 4.0 version of documentation. Click here to switch to the newest 7.0 version.
    We can help you with migration to the latest RavenDB
    Contact Us Now
    See on GitHub

    Cluster Observer

    • The primary goal of the Cluster Observer is to monitor the health of each database in the cluster
      and adjust its topology to maintain the desired Replication Factor.

    • This observer is always running on the Leader node.

    Operation Flow

    • In order to maintain the Replication Factor, every newly elected Leader starts measuring the health of each node by creating dedicated maintenance TCP connections to all other nodes in the cluster.

    • Each node reports the current status of all its databases in intervals of 250 milliseconds (by default).
      The Cluster Observer will consume those reports every 500 milliseconds (by default).

    • Upon a node failure, the Dynamic Database Distribution sequence
      will take place in order to ensure that the Replication Factor does not change.

    Note

    The Cluster Observer stores its information in memory, so when the Leader loses its leadership, the collected reports of the Cluster Observer and its decisions log are lost.

    Interacting with the Cluster Observer

    • You can interact with the Cluster Observer via the Studio, or with the following REST API calls:
    URL Method Query Params. Description
    /admin/cluster/observer/suspend POST value=[bool] Setting false will suspend the Cluster Observer operation for the current Leader term.
    /admin/cluster/observer/decisions GET Fetch the log of the recent decisions made by the cluster observer.
    /admin/cluster/maintenance-stats GET Fetch the latest reports of the Cluster Observer

    For example:

    • Let us assume a five-node cluster with servers A, B, C, D, E.
      We create a database with a replication factor of 3 and define an ETL task.

    • The newly created database will be distributed automatically to three of the cluster nodes.
      Let's assume it is distributed to B, C, and E (so the database group is [B,C,E]),
      and the cluster decides that node C is responsible for performing the ETL task.

    • If node C goes offline or becomes unreachable, the Cluster Observer detects the issue. Initially:

      • After the duration specified in the Cluster.TimeBeforeMovingToRehabInSec configuration,
        the observer moves node C to rehab mode, allowing time for recovery.
      • The ETL task fails over to another available node in the Database Group.

    • If node C remains offline beyond the period specified in the Cluster.TimeBeforeAddingReplicaInSec configuration, the observer begins replicating the database to another node in the Database Group as a last resort.

    related articlesRelated Articles

    Home / Docs / Server / Clustering / Distribution / Cluster Observer