Manager nodes are responsible for the Aspire UI, crawl control, the allocation of work to worker nodes and monitoring nodes which are down and taking corrective actions (such as designating a new main manager node and correcting the status of items that were being processed during failure).
A manager node is responsible for the seeds actively being crawled. Where there is more than one manager, a seed and all the documents it contains, are the sole responsibility of one manager. Seeds that are controlled by the same throttle policy are assigned to same manager node, so these seeds can be throttled together. Allocation of seeds to managers is performed at the time a crawl starts. Where there is more than one manager in a system, responsibility for seeds is distributed across the managers as evenly as possible, within the constraints imposed by the throttle policies.
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One of the manager nodes is designated as the main manager. This manager is responsible for:
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When a manager starts, if a main manager is already running, the manager will assume a “non-main” role.
A single main manager node must always exist, and so when a manager starts, or when a manager node fails, the managers co-ordinate to ensure that an active main manager exists. On start-up, a manager will check that an active main manager exists. If it does, then the manager simply joins the cluster. If an active main manager does not exist, the managers collaborate to choose a new main manager.