Restore xpack.ilm.enabled and xpack.slm.enabled settings (elastic#57383)

In elastic#55592 and elastic#55416, we deprecated the settings for enabling and disabling
basic license features and turned those settings into no-ops. Since doing so,
we've had feedback that this change may not give users enough time to cleanly
switch from non-ILM index management tools to ILM. If two index managers
operate simultaneously, results could be strange and difficult to
reconstruct. We don't know of any cases where SLM will cause a problem, but we
are restoring that setting as well, to be on the safe side.

This PR is not a strict commit reversion. First, we are keeping the new
xpack.watcher.use_ilm_index_management setting, introduced when
xpack.ilm.enabled was made a no-op, so that users can begin migrating to using
it. Second, the SLM setting was modified in the same commit as a group of other
settings, so I have taken just the changes relating to SLM.

Author: williamrandolph

docs/reference/migration/migrate_7_8.asciidoc

@@ -94,26 +94,30 @@ setting.
 
 [[deprecate-basic-license-feature-enabled]]
 
-.Several {xpack} settings no longer have any effect and are deprecated. 
+.Several {xpack} settings no longer have any effect and are deprecated.
 
 [%collapsible]
 ====
 *Details* +
-Basic {xpack} license features are always enabled for the {default-dist} 
-and the following settings no longer have any effect: 
+Basic {xpack} license features are always enabled for the {default-dist}
+and the following settings no longer have any effect:
 
 * `xpack.enrich.enabled`
 * `xpack.flattened.enabled`
-* `xpack.ilm.enabled`
 * `xpack.monitoring.enabled`
 * `xpack.rollup.enabled`
-* `xpack.slm.enabled`
 * `xpack.sql.enabled`
 * `xpack.transform.enabled`
 * `xpack.vectors.enabled`
 
 Previously, they could be set to `false` to disable the feature's APIs in a cluster.
 
+The ILM and SLM settings have been deprecated, but still have the effect of disabling
+their respective APIs:
+
+* `xpack.ilm.enabled`
+* `xpack.slm.enabled`
+
 *Impact* +
 To avoid deprecation warnings, discontinue use of these settings.
 If you have disabled ILM so that you can use another tool to manage Watcher

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/XPackSettings.java

@@ -118,17 +118,13 @@ private XPackSettings() {
 
     /**
      * Setting for enabling or disabling the index lifecycle extension. Defaults to true.
-     * <p>
-     * This setting is now a no-op: setting it to false is permitted, but does nothing.
      */
     @Deprecated // since 7.8.0
     public static final Setting<Boolean> INDEX_LIFECYCLE_ENABLED = Setting.boolSetting("xpack.ilm.enabled", true,
         Property.NodeScope, Property.Deprecated);
 
     /**
      * Setting for enabling or disabling the snapshot lifecycle extension. Defaults to true.
-     * <p>
-     * This setting is now a no-op: setting it to false is permitted, but does nothing.
      */
     @Deprecated // since = "7.8.0"
     public static final Setting<Boolean> SNAPSHOT_LIFECYCLE_ENABLED = Setting.boolSetting("xpack.slm.enabled", true,

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ilm/IndexLifecycleFeatureSetUsage.java

@@ -49,12 +49,12 @@ public void writeTo(StreamOutput out) throws IOException {
         }
     }
 
-    public IndexLifecycleFeatureSetUsage(boolean available) {
-        this(available, null);
+    public IndexLifecycleFeatureSetUsage(boolean available, boolean enabled) {
+        this(available, enabled, null);
     }
 
-    public IndexLifecycleFeatureSetUsage(boolean available, List<PolicyStats> policyStats) {
-        super(XPackField.INDEX_LIFECYCLE, available, true);
+    public IndexLifecycleFeatureSetUsage(boolean available, boolean enabled, List<PolicyStats> policyStats) {
+        super(XPackField.INDEX_LIFECYCLE, available, enabled);
         this.policyStats = policyStats;
     }
 

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/slm/SLMFeatureSetUsage.java

@@ -33,8 +33,8 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeOptionalWriteable(this.slmStats);
     }
 
-    public SLMFeatureSetUsage(boolean available, @Nullable SnapshotLifecycleStats slmStats) {
-        super(XPackField.SNAPSHOT_LIFECYCLE, available, true);
+    public SLMFeatureSetUsage(boolean available, boolean enabled, @Nullable SnapshotLifecycleStats slmStats) {
+        super(XPackField.SNAPSHOT_LIFECYCLE, available, enabled);
         this.slmStats = slmStats;
     }
 

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/template/IndexTemplateRegistry.java

@@ -26,6 +26,7 @@
 import org.elasticsearch.gateway.GatewayService;
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.xpack.core.XPackClient;
+import org.elasticsearch.xpack.core.XPackSettings;
 import org.elasticsearch.xpack.core.ilm.IndexLifecycleMetadata;
 import org.elasticsearch.xpack.core.ilm.LifecyclePolicy;
 import org.elasticsearch.xpack.core.ilm.action.PutLifecycleAction;
@@ -202,26 +203,29 @@ public void onFailure(Exception e) {
     }
 
     private void addIndexLifecyclePoliciesIfMissing(ClusterState state) {
+        boolean ilmSupported = XPackSettings.INDEX_LIFECYCLE_ENABLED.get(settings);
 
-        Optional<IndexLifecycleMetadata> maybeMeta = Optional.ofNullable(state.metadata().custom(IndexLifecycleMetadata.TYPE));
-        List<LifecyclePolicy> policies = getPolicyConfigs().stream()
-            .map(policyConfig -> policyConfig.load(xContentRegistry))
-            .collect(Collectors.toList());
+        if (ilmSupported) {
+            Optional<IndexLifecycleMetadata> maybeMeta = Optional.ofNullable(state.metadata().custom(IndexLifecycleMetadata.TYPE));
+            List<LifecyclePolicy> policies = getPolicyConfigs().stream()
+                .map(policyConfig -> policyConfig.load(xContentRegistry))
+                .collect(Collectors.toList());
 
-        for (LifecyclePolicy policy : policies) {
-            final AtomicBoolean creationCheck = policyCreationsInProgress.computeIfAbsent(policy.getName(),
-                key -> new AtomicBoolean(false));
-            if (creationCheck.compareAndSet(false, true)) {
-                final boolean policyNeedsToBeCreated = maybeMeta
-                    .flatMap(ilmMeta -> Optional.ofNullable(ilmMeta.getPolicies().get(policy.getName())))
-                    .isPresent() == false;
-                if (policyNeedsToBeCreated) {
-                    logger.debug("adding lifecycle policy [{}] for [{}], because it doesn't exist", policy.getName(), getOrigin());
-                    putPolicy(policy, creationCheck);
-                } else {
-                    logger.trace("not adding lifecycle policy [{}] for [{}], because it already exists",
-                        policy.getName(), getOrigin());
-                    creationCheck.set(false);
+            for (LifecyclePolicy policy : policies) {
+                final AtomicBoolean creationCheck = policyCreationsInProgress.computeIfAbsent(policy.getName(),
+                    key -> new AtomicBoolean(false));
+                if (creationCheck.compareAndSet(false, true)) {
+                    final boolean policyNeedsToBeCreated = maybeMeta
+                        .flatMap(ilmMeta -> Optional.ofNullable(ilmMeta.getPolicies().get(policy.getName())))
+                        .isPresent() == false;
+                    if (policyNeedsToBeCreated) {
+                        logger.debug("adding lifecycle policy [{}] for [{}], because it doesn't exist", policy.getName(), getOrigin());
+                        putPolicy(policy, creationCheck);
+                    } else {
+                        logger.trace("not adding lifecycle policy [{}] for [{}], because it already exists",
+                            policy.getName(), getOrigin());
+                        creationCheck.set(false);
+                    }
                 }
             }
         }

x-pack/plugin/core/src/main/resources/org/elasticsearch/xpack/core/ml/anomalydetection/state_index_template.json

@@ -8,9 +8,8 @@
     "index" : {
       "auto_expand_replicas" : "0-1",
       "hidden": true
-    },
-    "index.lifecycle.name": "${xpack.ml.index.lifecycle.name}",
-    "index.lifecycle.rollover_alias": "${xpack.ml.index.lifecycle.rollover_alias}"
+    }
+    ${xpack.ml.index.lifecycle.settings}
   },
   "mappings" : {
     "_doc": {

x-pack/plugin/core/src/main/resources/org/elasticsearch/xpack/core/ml/stats_index_template.json

@@ -9,9 +9,8 @@
       "number_of_shards" : "1",
       "auto_expand_replicas" : "0-1",
       "hidden": true
-    },
-    "index.lifecycle.name": "${xpack.ml.index.lifecycle.name}",
-    "index.lifecycle.rollover_alias": "${xpack.ml.index.lifecycle.rollover_alias}"
+    }
+    ${xpack.ml.index.lifecycle.settings}
   },
   "mappings" : ${xpack.ml.stats.mappings},
   "aliases" : {}

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ilm/IndexLifecycleFeatureSetUsageTests.java

@@ -28,18 +28,22 @@ protected IndexLifecycleFeatureSetUsage createTestInstance() {
                 policyStats.add(PolicyStatsTests.createRandomInstance());
             }
         }
-        return new IndexLifecycleFeatureSetUsage(available, policyStats);
+        return new IndexLifecycleFeatureSetUsage(available, enabled, policyStats);
     }
 
     @Override
     protected IndexLifecycleFeatureSetUsage mutateInstance(IndexLifecycleFeatureSetUsage instance) throws IOException {
         boolean available = instance.available();
+        boolean enabled = instance.enabled();
         List<PolicyStats> policyStats = instance.getPolicyStats();
-        switch (between(0, 1)) {
+        switch (between(0, 2)) {
         case 0:
             available = available == false;
             break;
         case 1:
+            enabled = enabled == false;
+            break;
+        case 2:
             if (policyStats == null) {
                 policyStats = new ArrayList<>();
                 policyStats.add(PolicyStatsTests.createRandomInstance());
@@ -53,7 +57,7 @@ protected IndexLifecycleFeatureSetUsage mutateInstance(IndexLifecycleFeatureSetU
         default:
             throw new AssertionError("Illegal randomisation branch");
         }
-        return new IndexLifecycleFeatureSetUsage(available, policyStats);
+        return new IndexLifecycleFeatureSetUsage(available, enabled, policyStats);
     }
 
     @Override