sigram commented on a change in pull request #1758:
URL: https://github.com/apache/lucene-solr/pull/1758#discussion_r473848530
##########
File path:
solr/core/src/java/org/apache/solr/cluster/events/ClusterSingleton.java
##########
@@ -0,0 +1,14 @@
+package org.apache.solr.cluster.events;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+/**
+ * Intended for {@link org.apache.solr.core.CoreContainer} plugins that should
be
+ * enabled only one instance per cluster.
+ * <p>Implementation detail: currently these plugins are instantiated on the
+ * Overseer leader, and closed when the current node loses its leadership.</p>
+ */
+@Retention(RetentionPolicy.RUNTIME)
+public @interface ClusterSingleton {
Review comment:
@chatman once again, this PR is NOT only about the autoscaling (even
though that was the original motivation). The whole point of this PR is for
Solr to provide a minimal facility that allows plugins to react to cluster-wide
events - and ONE particular application would be to re-implement the
autoscaling triggers.
Without this API each package (autoscaling or any other package that needs
it) would have to re-implement the notion of cluster-wide event monitoring and
generation.
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