Add default snapshot repo cluster setting

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/repositories/10_default_repository.yml

@@ -0,0 +1,172 @@
+---
+setup:
+  - requires:
+      test_runner_features: [capabilities]
+      capabilities:
+        - method: PUT
+          path: /_cluster/settings
+          capabilities: ["repositories.default_repository_setting"]
+      reason: "Default repository setting capability check"
+
+  # Create two test repositories without verification
+  - do:
+      snapshot.create_repository:
+        repository: test_repo_1
+        verify: false
+        body:
+          type: fs
+          settings:
+            location: "test_repo_1_loc"
+
+  - do:
+      snapshot.create_repository:
+        repository: test_repo_2
+        verify: false
+        body:
+          type: fs
+          settings:
+            location: "test_repo_2_loc"
+
+---
+teardown:
+  # Clean up cluster settings
+  - do:
+      cluster.put_settings:
+        body:
+          persistent:
+            repositories.default_repository: null
+
+  # Clean up repositories (if they still exist)
+  - do:
+      catch: missing
+      snapshot.delete_repository:
+        repository: test_repo_1
+
+  - do:
+      catch: missing
+      snapshot.delete_repository:
+        repository: test_repo_2
+
+---
+"Set and validate default repository":
+  # Set first repo as default
+  - do:
+      cluster.put_settings:
+        body:
+          persistent:
+            repositories.default_repository: "test_repo_1"
+
+  - match: { persistent.repositories.default_repository: "test_repo_1" }
+
+  # Verify the setting is persisted
+  - do:
+      cluster.get_settings: {}
+
+  - match: { persistent.repositories.default_repository: "test_repo_1" }
+
+---
+"Cannot delete default repository":
+  # Set first repo as default
+  - do:
+      cluster.put_settings:
+        body:
+          persistent:
+            repositories.default_repository: "test_repo_1"
+
+  # Try to delete the default repository - should fail
+  - do:
+      catch: /cannot delete the default repository/
+      snapshot.delete_repository:
+        repository: test_repo_1
+
+  # Verify repo still exists
+  - do:
+      snapshot.get_repository:
+        repository: test_repo_1
+
+  - is_true: test_repo_1
+
+---
+"Cannot set non-existent repository as default":
+  # Try to set a non-existent repository as default
+  - do:
+      catch: /Repository \[non_existent_repo\] is not registered/
+      cluster.put_settings:
+        body:
+          persistent:
+            repositories.default_repository: "non_existent_repo"
+
+---
+"Change default repository and delete previous default":
+  # Set first repo as default
+  - do:
+      cluster.put_settings:
+        body:
+          persistent:
+            repositories.default_repository: "test_repo_1"
+
+  # Change default to second repo
+  - do:
+      cluster.put_settings:
+        body:
+          persistent:
+            repositories.default_repository: "test_repo_2"
+
+  - match: { persistent.repositories.default_repository: "test_repo_2" }
+
+  # Now we can delete first repo (no longer default)
+  - do:
+      snapshot.delete_repository:
+        repository: test_repo_1
+
+  - match: { acknowledged: true }
+
+  # Verify first repo is gone
+  - do:
+      catch: missing
+      snapshot.get_repository:
+        repository: test_repo_1
+
+  # Verify second repo still exists and is default
+  - do:
+      snapshot.get_repository:
+        repository: test_repo_2
+
+  - is_true: test_repo_2
+
+  - do:
+      cluster.get_settings: {}
+
+  - match: { persistent.repositories.default_repository: "test_repo_2" }
+
+---
+"Clear default repository setting":
+  # Set a repository as default
+  - do:
+      cluster.put_settings:
+        body:
+          persistent:
+            repositories.default_repository: "test_repo_1"
+
+  # Clear the default by setting to null
+  - do:
+      cluster.put_settings:
+        body:
+          persistent:
+            repositories.default_repository: null
+
+  - match: { persistent: {} }
+
+  # Verify the setting is cleared
+  - do:
+      cluster.get_settings: {}
+
+  - is_false: persistent.repositories.default_repository
+
+  # Now we can delete the repository
+  - do:
+      snapshot.delete_repository:
+        repository: test_repo_1
+
+  - match: { acknowledged: true }
+

server/src/main/java/org/elasticsearch/common/settings/ClusterSettings.java

@@ -123,6 +123,7 @@
 import org.elasticsearch.persistent.decider.EnableAssignmentDecider;
 import org.elasticsearch.plugins.PluginsService;
 import org.elasticsearch.readiness.ReadinessService;
+import org.elasticsearch.repositories.RepositoriesService;
 import org.elasticsearch.repositories.blobstore.BlobStoreRepository;
 import org.elasticsearch.repositories.fs.FsRepository;
 import org.elasticsearch.rest.BaseRestHandler;
@@ -589,6 +590,7 @@ public void apply(Settings value, Settings current, Settings previous) {
         HandshakingTransportAddressConnector.PROBE_CONNECT_TIMEOUT_SETTING,
         HandshakingTransportAddressConnector.PROBE_HANDSHAKE_TIMEOUT_SETTING,
         SnapshotsService.MAX_CONCURRENT_SNAPSHOT_OPERATIONS_SETTING,
+        RepositoriesService.DEFAULT_REPOSITORY_SETTING,
         RestoreService.REFRESH_REPO_UUID_ON_RESTORE_SETTING,
         FsHealthService.ENABLED_SETTING,
         FsHealthService.REFRESH_INTERVAL_SETTING,

server/src/main/java/org/elasticsearch/repositories/RepositoriesService.java

@@ -111,6 +111,16 @@ public class RepositoriesService extends AbstractLifecycleComponent implements C
         Setting.Property.NodeScope
     );
 
+    /**
+     * Setting that specifies the default repository to use for snapshot and restore operations when no repository is explicitly
+     * specified. If not set, some snapshot and restore operations may require an explicit repository name.
+     */
+    public static final Setting<String> DEFAULT_REPOSITORY_SETTING = Setting.simpleString(
+        "repositories.default_repository",
+        Setting.Property.NodeScope,
+        Setting.Property.Dynamic
+    );
+
     private final Map<String, Repository.Factory> typesRegistry;
     private final Map<String, Repository.Factory> internalTypesRegistry;
 
@@ -125,6 +135,8 @@ public class RepositoriesService extends AbstractLifecycleComponent implements C
 
     private final List<BiConsumer<Snapshot, IndexVersion>> preRestoreChecks;
 
+    private volatile String defaultRepository;
+
     @SuppressWarnings("this-escape")
     public RepositoriesService(
         Settings settings,
@@ -154,9 +166,74 @@ public RepositoriesService(
             threadPool.relativeTimeInMillisSupplier()
         );
         this.preRestoreChecks = preRestoreChecks;
+        this.defaultRepository = DEFAULT_REPOSITORY_SETTING.get(settings);
+        clusterService.getClusterSettings()
+            .addSettingsUpdateConsumer(DEFAULT_REPOSITORY_SETTING, this::setDefaultRepository, this::validateDefaultRepository);
         snapshotMetrics.createSnapshotShardsInProgressMetric(this::getShardSnapshotsInProgress);
     }
 
+    /**
+     * Gets the configured default repository.
+     *
+     * @return the default repository name, or an empty string if not configured
+     */
+    public String getDefaultRepository() {
+        return defaultRepository;
+    }
+
+    /**
+     * Sets the default repository value.
+     * This is called by the settings update consumer when the setting changes.
+     *
+     * @param repositoryName the new default repository name
+     */
+    private void setDefaultRepository(String repositoryName) {
+        this.defaultRepository = repositoryName;
+        logger.info("Default repository set to [{}]", repositoryName);
+    }
+
+    /**
+     * Validates that the default repository is registered.
+     * This validator is called when the default repository setting is updated.
+     * Empty strings are allowed to clear the default repository setting.
+     *
+     * @param repositoryName the repository name to validate
+     * @throws IllegalArgumentException if the repository name is not empty and the repository doesn't exist
+     */
+    private void validateDefaultRepository(String repositoryName) {
+        if (Strings.isEmpty(repositoryName)) {
+            logger.info("Default repository cleared");
+            return;
+        }
+        if (isRepositoryRegistered(repositoryName) == false) {
+            throw new IllegalArgumentException(
+                "Repository ["
+                    + repositoryName
+                    + "] is not registered. "
+                    + "Cannot set as default repository. Please register the repository prior to setting as default using PUT /_snapshot/"
+                    + repositoryName
+            );
+        }
+    }
+
+    /**
+     * Checks if a repository is registered in the default project, any other project, or internal repositories.
+     *
+     * @param repositoryName the repository name to check
+     * @return true if the repository is registered, false otherwise
+     */
+    private boolean isRepositoryRegistered(String repositoryName) {
+        if (repositoryOrNull(ProjectId.DEFAULT, repositoryName) != null) {
+            return true;
+        }
+        boolean found = repositories.values().stream().anyMatch(projectRepos -> projectRepos.containsKey(repositoryName));
+        if (found) {
+            return true;
+        }
+        found = internalRepositories.values().stream().anyMatch(projectRepos -> projectRepos.containsKey(repositoryName));
+        return found;
+    }
+
     /**
      * Registers new repository in the cluster
      * <p>
@@ -568,6 +645,7 @@ public ClusterState execute(ClusterState currentState) {
                 for (RepositoryMetadata repositoryMetadata : repositories.repositories()) {
                     if (Regex.simpleMatch(request.name(), repositoryMetadata.name())) {
                         ensureRepositoryNotInUse(projectState, repositoryMetadata.name());
+                        ensureRepositoryNotDefault(currentState, repositoryMetadata.name());
                         ensureNoSearchableSnapshotsIndicesInUse(currentState, repositoryMetadata);
                         deletedRepositories.add(repositoryMetadata.name());
                         changed = true;
@@ -1135,6 +1213,24 @@ private static void ensureRepositoryNotInUse(ProjectState projectState, String r
         }
     }
 
+    /**
+     * Ensures that the repository being deleted is not currently set as the default repository.
+     *
+     * @param currentState the current cluster state
+     * @param repository the repository name to check
+     * @throws RepositoryException if the repository is the default repository
+     */
+    private static void ensureRepositoryNotDefault(ClusterState currentState, String repository) {
+        String defaultRepository = DEFAULT_REPOSITORY_SETTING.get(currentState.metadata().settings());
+        if (Strings.isEmpty(defaultRepository) == false && repository.equals(defaultRepository)) {
+            throw newRepositoryConflictException(
+                repository,
+                "cannot delete the default repository. Please change the default repository cluster setting "
+                    + "repositories.default_repository before deleting this repository."
+            );
+        }
+    }
+
     public static boolean isReadOnly(Settings repositorySettings) {
         return Boolean.TRUE.equals(repositorySettings.getAsBoolean(BlobStoreRepository.READONLY_SETTING_KEY, null));
     }

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestClusterUpdateSettingsAction.java

@@ -33,6 +33,9 @@ public class RestClusterUpdateSettingsAction extends BaseRestHandler {
     private static final String PERSISTENT = "persistent";
     private static final String TRANSIENT = "transient";
 
+    public static final String SUPPORTS_DEFAULT_REPO_SETTING = "repositories.default_repository_setting";
+    private static final Set<String> CAPABILITIES = Set.of(SUPPORTS_DEFAULT_REPO_SETTING);
+
     @Override
     public List<Route> routes() {
         return List.of(new Route(PUT, "/_cluster/settings"));
@@ -74,4 +77,8 @@ public boolean canTripCircuitBreaker() {
         return false;
     }
 
+    @Override
+    public Set<String> supportedCapabilities() {
+        return CAPABILITIES;
+    }
 }

server/src/test/java/org/elasticsearch/action/admin/cluster/repositories/reservedstate/ReservedRepositoryActionTests.java

@@ -17,6 +17,7 @@
 import org.elasticsearch.cluster.metadata.ProjectMetadata;
 import org.elasticsearch.cluster.metadata.RepositoryMetadata;
 import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.repositories.RepositoriesService;
 import org.elasticsearch.repositories.Repository;
@@ -39,6 +40,7 @@
 import static org.mockito.Mockito.doAnswer;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.when;
 
 /**
  * Tests that the ReservedRepositoryAction does validation, can add and remove repositories
@@ -144,10 +146,14 @@ public Repository create(ProjectId projectId, RepositoryMetadata metadata) {
         };
 
         ThreadPool threadPool = mock(ThreadPool.class);
+        ClusterService clusterService = mock(ClusterService.class);
+        when(clusterService.getClusterSettings()).thenReturn(
+            new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS)
+        );
         RepositoriesService repositoriesService = spy(
             new RepositoriesService(
                 Settings.EMPTY,
-                mock(ClusterService.class),
+                clusterService,
                 Map.of(),
                 Map.of("fs", fsFactory),
                 threadPool,

server/src/test/java/org/elasticsearch/indices/cluster/IndicesClusterStateServiceRandomUpdatesTests.java

@@ -38,6 +38,7 @@
 import org.elasticsearch.cluster.routing.allocation.FailedShard;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.UUIDs;
+import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.util.set.Sets;
 import org.elasticsearch.index.Index;
@@ -542,6 +543,9 @@ private IndicesClusterStateService createIndicesClusterStateService(
             Collections.emptySet()
         );
         final ClusterService clusterService = mock(ClusterService.class);
+        when(clusterService.getClusterSettings()).thenReturn(
+            new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS)
+        );
         final NodeClient client = mock(NodeClient.class);
         final RepositoriesService repositoriesService = new RepositoriesService(
             settings,