[7.x] Enforce data_frozen for partial searchable snapshot _tier_prefe…

…rence (#71155) (#71342)

* Enforce data_frozen for partial searchable snapshot _tier_preference (#71155)

We already set `data_frozen` for partial searchable snapshots when they are mounted (#70786), and
automatically convert values other than the frozen role automatically for these snapshots when the
metadata is loaded (#71014). This commit makes the `_tier_preference` setting validate that the
setting is *only* `data_frozen` when set on a partial searchable snapshot index.

* Handle mixed version clusters with pre-7.13.0 frozen SBIs

* Fix checkstyyyyyyyyle

* Pass index version in settings for test

* Unconditionally return only data_frozen for setting

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/cluster/routing/allocation/DataTierAllocationDecider.java

@@ -31,6 +31,7 @@
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
+import java.util.function.Function;
 import java.util.stream.Collectors;
 
 import static org.elasticsearch.xpack.core.DataTier.DATA_FROZEN;
@@ -65,8 +66,21 @@ public class DataTierAllocationDecider extends AllocationDecider {
         VALIDATOR, Setting.Property.Dynamic, Setting.Property.IndexScope);
     public static final Setting<String> INDEX_ROUTING_EXCLUDE_SETTING = Setting.simpleString(INDEX_ROUTING_EXCLUDE,
         VALIDATOR, Setting.Property.Dynamic, Setting.Property.IndexScope);
-    public static final Setting<String> INDEX_ROUTING_PREFER_SETTING = Setting.simpleString(INDEX_ROUTING_PREFER,
-        VALIDATOR, Setting.Property.Dynamic, Setting.Property.IndexScope);
+    public static final Setting<String> INDEX_ROUTING_PREFER_SETTING = new Setting<String>(new Setting.SimpleKey(INDEX_ROUTING_PREFER),
+        DataTierValidator::getDefaultTierPreference, Function.identity(), VALIDATOR,
+        Setting.Property.Dynamic, Setting.Property.IndexScope) {
+        @Override
+        public String get(Settings settings) {
+            if (SearchableSnapshotsConstants.isPartialSearchableSnapshotIndex(settings)) {
+                // Partial searchable snapshot indices should be restricted to
+                // only data_frozen when reading the setting, or else validation fails.
+                return DATA_FROZEN;
+            } else {
+                // Otherwise pass through to the regular setting retrieval
+                return super.get(settings);
+            }
+        }
+    };
 
     private static void validateTierSetting(String setting) {
         if (Strings.hasText(setting)) {
@@ -84,17 +98,32 @@ private static class DataTierValidator implements Setting.Validator<String> {
             org.elasticsearch.common.collect.List.of(IndexModule.INDEX_STORE_TYPE_SETTING,
                 SearchableSnapshotsConstants.SNAPSHOT_PARTIAL_SETTING);
 
+        public static String getDefaultTierPreference(Settings settings) {
+            if (SearchableSnapshotsConstants.isPartialSearchableSnapshotIndex(settings)) {
+                return DATA_FROZEN;
+            } else {
+                return "";
+            }
+        }
+
         @Override
         public void validate(String value) {
             validateTierSetting(value);
         }
 
         @Override
-        public void validate(String value, Map<Setting<?>, Object> settings) {
-            if (Strings.hasText(value) && SearchableSnapshotsConstants.isPartialSearchableSnapshotIndex(settings) == false) {
-                String[] split = value.split(",");
-                if (Arrays.stream(split).anyMatch(DATA_FROZEN::equals)) {
-                    throw new IllegalArgumentException("[" + DATA_FROZEN + "] tier can only be used for partial searchable snapshots");
+        public void validate(String value, Map<Setting<?>, Object> settings, boolean exists) {
+            if (exists && value != null) {
+                if (SearchableSnapshotsConstants.isPartialSearchableSnapshotIndex(settings)) {
+                    if (value.equals(DATA_FROZEN) == false) {
+                        throw new IllegalArgumentException("only the [" + DATA_FROZEN +
+                            "] tier preference may be used for partial searchable snapshots (got: [" + value + "])");
+                    }
+                } else {
+                    String[] split = value.split(",");
+                    if (Arrays.stream(split).anyMatch(DATA_FROZEN::equals)) {
+                        throw new IllegalArgumentException("[" + DATA_FROZEN + "] tier can only be used for partial searchable snapshots");
+                    }
                 }
             }
         }

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

@@ -42,6 +42,11 @@ public static boolean isPartialSearchableSnapshotIndex(Map<Setting<?>, Object> i
             && (boolean) indexSettings.get(SNAPSHOT_PARTIAL_SETTING);
     }
 
+    public static boolean isPartialSearchableSnapshotIndex(Settings indexSettings) {
+        return SNAPSHOT_DIRECTORY_FACTORY_KEY.equals(INDEX_STORE_TYPE_SETTING.get(indexSettings))
+            && SNAPSHOT_PARTIAL_SETTING.get(indexSettings);
+    }
+
     public static final String CACHE_FETCH_ASYNC_THREAD_POOL_NAME = "searchable_snapshots_cache_fetch_async";
     public static final String CACHE_FETCH_ASYNC_THREAD_POOL_SETTING = "xpack.searchable_snapshots.cache_fetch_async_thread_pool";
 

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/cluster/routing/allocation/DataTierAllocationDeciderTests.java

@@ -730,22 +730,26 @@ public void testFrozenIllegalForRegularIndices() {
     }
 
     public void testFrozenLegalForPartialSnapshot() {
-        List<String> tierList = new ArrayList<>(randomSubsetOf(DataTier.ALL_DATA_TIERS));
-        if (tierList.contains(DATA_FROZEN) == false) {
-            tierList.add(DATA_FROZEN);
-        }
-        Randomness.shuffle(tierList);
-
-        String value = Strings.join(tierList, ",");
         Setting<String> setting = randomTierSetting();
-        Settings.Builder builder = Settings.builder().put(setting.getKey(), value);
+        Settings.Builder builder = Settings.builder().put(setting.getKey(), DATA_FROZEN);
         builder.put(IndexModule.INDEX_STORE_TYPE_SETTING.getKey(), SearchableSnapshotsConstants.SNAPSHOT_DIRECTORY_FACTORY_KEY);
         builder.put(SearchableSnapshotsConstants.SNAPSHOT_PARTIAL_SETTING.getKey(), true);
 
         Settings settings = builder.build();
 
         // validate do not throw
-        assertThat(setting.get(settings), equalTo(value));
+        assertThat(setting.get(settings), equalTo(DATA_FROZEN));
+    }
+
+    public void testDefaultValueForPreference() {
+        assertThat(DataTierAllocationDecider.INDEX_ROUTING_PREFER_SETTING.get(Settings.EMPTY), equalTo(""));
+
+        Settings.Builder builder = Settings.builder();
+        builder.put(IndexModule.INDEX_STORE_TYPE_SETTING.getKey(), SearchableSnapshotsConstants.SNAPSHOT_DIRECTORY_FACTORY_KEY);
+        builder.put(SearchableSnapshotsConstants.SNAPSHOT_PARTIAL_SETTING.getKey(), true);
+
+        Settings settings = builder.build();
+        assertThat(DataTierAllocationDecider.INDEX_ROUTING_PREFER_SETTING.get(settings), equalTo(DATA_FROZEN));
     }
 
     public Setting<String> randomTierSetting() {