EQL: limit CCS to v 7.15 (#91834)

Author: luigidellaquila

docs/changelog/91834.yaml

@@ -0,0 +1,6 @@
+pr: 91834
+summary: Limit CCS to v 7.15
+area: EQL
+type: bug
+issues:
+ - 91762

docs/reference/eql/eql-search-api.asciidoc

@@ -47,8 +47,9 @@ or alias.
 
 * See <<eql-required-fields>>.
 
-* experimental:[] For cross-cluster search, the local and remote clusters must
-use the same {es} version. For security, see <<remote-clusters-security>>.
+* experimental:[] For cross-cluster search, the local and remote clusters must use the same {es} version.
+Local clusters version 7.17.7 or later also support cross-cluster search to remote clusters version 7.15.0 or later.
+For security, see <<remote-clusters-security>>.
 
 [[eql-search-api-limitations]]
 ===== Limitations

docs/reference/eql/eql.asciidoc

@@ -800,6 +800,8 @@ experimental::[]
 The EQL search API supports <<modules-cross-cluster-search,cross-cluster
 search>>. However, the local and <<remote-clusters,remote clusters>>
 must use the same {es} version.
+Local clusters version 7.17.7 or later also support <<modules-cross-cluster-search,cross-cluster
+search>> to <<remote-clusters,remote clusters>> version 7.15.0 or later.
 
 The following <<cluster-update-settings,cluster update settings>> request
 adds two remote clusters: `cluster_one` and `cluster_two`.

docs/reference/search/search-your-data/search-across-clusters.asciidoc

@@ -439,6 +439,8 @@ in the following matrix.
 
 IMPORTANT: For the <<eql-search-api,EQL search API>>, the local and remote
 clusters must use the same {es} version.
+Local clusters version 7.17.7 or later also support cross-cluster search to
+<<remote-clusters,remote clusters>> version 7.15.0 or later.
 
 [%collapsible%open]
 .Version compatibility matrix

x-pack/plugin/eql/qa/ccs-rolling-upgrade/build.gradle

@@ -7,7 +7,6 @@
  */
 
 
-import org.elasticsearch.gradle.Version
 import org.elasticsearch.gradle.internal.info.BuildParams
 import org.elasticsearch.gradle.testclusters.StandaloneRestIntegTestTask
 
@@ -20,8 +19,8 @@ dependencies {
   testImplementation project(':client:rest-high-level')
 }
 
-// EQL was released as GA in v 7.11.0
-BuildParams.bwcVersions.withWireCompatiple(v -> v.onOrAfter("7.11.0")) { bwcVersion, baseName ->
+// see org.elasticsearch.xpack.eql.util.RemoteClusterRegistry.FIRST_COMPATIBLE_VERSION
+BuildParams.bwcVersions.withWireCompatiple(v -> v.onOrAfter("7.15.0")) { bwcVersion, baseName ->
 
   /**
    * We execute tests 3 times.

x-pack/plugin/eql/src/main/java/org/elasticsearch/xpack/eql/util/RemoteClusterRegistry.java

@@ -14,6 +14,7 @@
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.transport.RemoteClusterAware;
 import org.elasticsearch.transport.RemoteClusterService;
+import org.elasticsearch.xpack.eql.execution.search.RuntimeUtils;
 
 import java.util.Set;
 import java.util.TreeSet;
@@ -25,6 +26,8 @@ public class RemoteClusterRegistry {
     private final IndexNameExpressionResolver indexNameExpressionResolver;
     private final ClusterService clusterService;
 
+    public static final Version FIRST_COMPATIBLE_VERSION = RuntimeUtils.SWITCH_TO_MULTI_VALUE_FIELDS_VERSION;
+
     public RemoteClusterRegistry(
         RemoteClusterService remoteClusterService,
         IndicesOptions indicesOptions,
@@ -41,8 +44,7 @@ public Set<String> versionIncompatibleClusters(String indexPattern) {
         Set<String> incompatibleClusters = new TreeSet<>();
         for (String clusterAlias : clusterAliases(Strings.splitStringByCommaToArray(indexPattern), true)) {
             Version clusterVersion = remoteClusterService.getConnection(clusterAlias).getVersion();
-            // EQL was released as GA in v 7.11.0
-            if (Version.CURRENT.isCompatible(clusterVersion) == false || clusterVersion.before(Version.V_7_11_0)) {
+            if (Version.CURRENT.isCompatible(clusterVersion) == false || clusterVersion.before(FIRST_COMPATIBLE_VERSION)) {
                 incompatibleClusters.add(clusterAlias);
             }
         }