Merge branch 'main' into handle-transform-reindex-failures

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/BwcVersions.java

@@ -252,6 +252,20 @@ private List<Version> getReleased() {
             .toList();
     }
 
+    public List<Version> getReadOnlyIndexCompatible() {
+        // Lucene can read indices in version N-2
+        int compatibleMajor = currentVersion.getMajor() - 2;
+        return versions.stream().filter(v -> v.getMajor() == compatibleMajor).sorted(Comparator.naturalOrder()).toList();
+    }
+
+    public void withLatestReadOnlyIndexCompatible(Consumer<Version> versionAction) {
+        var compatibleVersions = getReadOnlyIndexCompatible();
+        if (compatibleVersions == null || compatibleVersions.isEmpty()) {
+            throw new IllegalStateException("No read-only compatible version found.");
+        }
+        versionAction.accept(compatibleVersions.getLast());
+    }
+
     /**
      * Return versions of Elasticsearch which are index compatible with the current version.
      */

docs/changelog/117583.yaml

@@ -0,0 +1,17 @@
+pr: 117583
+summary: Removing index alias creation for deprecated transforms notification index
+area: Machine Learning
+type: deprecation
+issues: []
+deprecation:
+  title: Removing index alias creation for deprecated transforms notification index
+  area: Transform
+  details: >-
+    As part of the migration from 7.x to 8.x, the `.data-frame-notifications-1` index
+    was deprecated and replaced with the `.transform-notifications-000002` index.
+    The index is no longer created by default, all writes are directed to the new index,
+    and any clusters with the deprecated index will have an alias created to ensure that
+    reads are still retrieving data that was written to the index before the migration to 8.x.
+    This change removes the alias from the deprecated index in 9.x. Any clusters with the alias present
+    will retain it, but it will not be created on new clusters.
+  impact: No known end user impact.