murblanc commented on a change in pull request #1758:
URL: https://github.com/apache/lucene-solr/pull/1758#discussion_r473052101
##########
File path:
solr/core/src/java/org/apache/solr/cluster/events/ClusterSingleton.java
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@@ -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:
Ok, I agree about keeping module dependencies clean. Didn't realize
"Solr-core" meant just a module in the project.
We do need some code in `solr-core` though, at least interfaces to be able
to interact with other modules without depending on them (+ dependency
injection or configuration to instantiate actual concrete classes).
I believe that understanding what's really needed happens when the
interfaces and the configuration is wired into Solr in some place or another,
then we should move out of solr-core everything left there without reason
(thinking of [PR 1684](https://github.com/apache/lucene-solr/pull/1684/files)
as I write this comment, likely the impl and plugin packages there can be moved
out of solr-core.
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