Andrzej Bialecki created SOLR-14749:
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Summary: Provide a clean API for cluster-level event processing
Key: SOLR-14749
URL: https://issues.apache.org/jira/browse/SOLR-14749
Project: Solr
Issue Type: Improvement
Security Level: Public (Default Security Level. Issues are Public)
Components: AutoScaling
Reporter: Andrzej Bialecki
Assignee: Andrzej Bialecki
This is a companion issue to SOLR-14613 and it aims at providing a clean,
strongly typed API for the functionality formerly known as "triggers" - that
is, a component for generating cluster-level events corresponding to changes in
the cluster state, and a pluggable API for processing these events.
The 8x triggers have been removed so this functionality is currently missing in
9.0. However, this functionality is crucial for implementing the automatic
collection repair and re-balancing as the cluster state changes (nodes going
down / up, becoming overloaded / unused / decommissioned, etc).
For this reason we need this API and a default implementation of triggers that
at least can perform automatic collection repair (maintaining the desired
replication factor in presence of live node changes).
As before, the actual changes to the collections will be executed using
existing CollectionAdmin API, which in turn may use the placement plugins from
SOLR-14613.
h3. Division of responsibility
* built-in Solr components (non-pluggable):
** cluster state monitoring and event generation,
** simple scheduler to periodically generate scheduled events
* plugins:
** automatic collection repair on {{nodeLost}} events (provided by default)
** re-balancing of replicas (periodic or on {{nodeAdded}} events)
** reporting (eg. requesting additional node provisioning)
** scheduled maintenance (eg. removing inactive shards after split)
h3. Other considerations
These plugins (unlike the placement plugins) need to execute on one designated
node in the cluster. Currently the easiest way to implement this is to run them
on the Overseer leader node.
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