configuration, naming and cleanup for load balancing

The strategies are now named plugins instead.
The configuration file now has defaults and examples.
The default policy can be overridden.

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/core/CausalClusteringSettings.java

@@ -314,16 +314,21 @@ public class CausalClusteringSettings implements LoadableConfig
     public static final Setting<List<String>> upstream_selection_strategy =
             setting( "causal_clustering.upstream_selection_strategy", list( ",", STRING ), "default" );
 
-    @Description( "The load balancing plugin to use. This must be the same for all core servers participating in the cluster." )
+    @Description( "Tags for the server used when configuring load balancing and replication policies." )
+    public static Setting<List<String>> server_tags =
+            setting( "causal_clustering.server_tags", list( ",", STRING ), "" );
+
+    @Description( "The load balancing plugin to use." )
     public static Setting<String> load_balancing_plugin =
             setting( "causal_clustering.load_balancing.plugin", STRING, "server_policies" );
 
-    @Description( "The configuration must be valid for the configured plugin." )
+    @Description( "The configuration must be valid for the configured plugin and usually exists" +
+                  "under matching subkeys, e.g. ..config.server_policies.*" +
+                  "This is just a top-level placeholder for the plugin-specific configuration." )
     public static Setting<String> load_balancing_config =
             setting( "causal_clustering.load_balancing.config", STRING, "" );
 
-    @Description( "Tags for the server used when configuring load balancing and replication policies." +
-                  " Multiple tags can be configured by separating with a comma." )
-    public static Setting<List<String>> server_tags =
-            setting( "causal_clustering.server_tags", list( ",", STRING ), "" );
+    @Description( "Enables shuffling of the returned load balancing result." )
+    public static final Setting<Boolean> load_balancing_shuffle =
+            setting( "causal_clustering.load_balancing.shuffle", BOOLEAN, "true" );
 }

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/core/EnterpriseCoreEditionModule.java

@@ -42,11 +42,12 @@
 import org.neo4j.causalclustering.discovery.procedures.ClusterOverviewProcedure;
 import org.neo4j.causalclustering.discovery.procedures.CoreRoleProcedure;
 import org.neo4j.causalclustering.identity.MemberId;
-import org.neo4j.causalclustering.load_balancing.LoadBalancingStrategy;
+import org.neo4j.causalclustering.load_balancing.LoadBalancingPlugin;
+import org.neo4j.causalclustering.load_balancing.plugins.ServerShufflingPlugin;
+import org.neo4j.causalclustering.load_balancing.plugins.server_policies.InvalidFilterSpecification;
+import org.neo4j.causalclustering.load_balancing.plugins.server_policies.ServerPoliciesPlugin;
 import org.neo4j.causalclustering.load_balancing.procedure.GetServersProcedureV1;
 import org.neo4j.causalclustering.load_balancing.procedure.GetServersProcedureV2;
-import org.neo4j.causalclustering.load_balancing.strategy.AllServersStrategy;
-import org.neo4j.causalclustering.load_balancing.strategy.ServerShufflingStrategy;
 import org.neo4j.causalclustering.logging.BetterMessageLogger;
 import org.neo4j.causalclustering.logging.MessageLogger;
 import org.neo4j.causalclustering.logging.NullMessageLogger;
@@ -110,17 +111,35 @@ public enum RaftLogImplementation
         IN_MEMORY, SEGMENTED
     }
 
+    private LoadBalancingPlugin getLoadBalancingPlugin()
+    {
+        LoadBalancingPlugin plugin;
+
+        try
+        {
+            // TODO: Select using services framework and plugin configuration.
+            plugin = new ServerPoliciesPlugin( topologyService, consensusModule.raftMachine(), logProvider, config );
+        }
+        catch ( InvalidFilterSpecification e )
+        {
+            throw new RuntimeException( e );
+        }
+
+        if ( config.get( CausalClusteringSettings.load_balancing_shuffle ) )
+        {
+            plugin = new ServerShufflingPlugin( plugin );
+        }
+        return plugin;
+    }
+
     @Override
     public void registerEditionSpecificProcedures( Procedures procedures ) throws KernelException
     {
-        LoadBalancingStrategy loadBalancingStrategy = new ServerShufflingStrategy(
-                new AllServersStrategy( topologyService, consensusModule.raftMachine(), config ) );
-
         procedures.registerProcedure( EnterpriseBuiltInDbmsProcedures.class, true );
         procedures.register(
                 new GetServersProcedureV1( topologyService, consensusModule.raftMachine(), config, logProvider ) );
         procedures.register(
-                new GetServersProcedureV2( loadBalancingStrategy ) );
+                new GetServersProcedureV2( getLoadBalancingPlugin() ) );
         procedures.register(
                 new ClusterOverviewProcedure( topologyService, consensusModule.raftMachine(), logProvider ) );
         procedures.register( new CoreRoleProcedure( consensusModule.raftMachine() ) );

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/LoadBalancingStrategy.java → enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/LoadBalancingPlugin.java

@@ -26,7 +26,7 @@
  * Defines the interface for an implementation of the GetServersV2
  * cluster discovery and load balancing procedure.
  */
-public interface LoadBalancingStrategy
+public interface LoadBalancingPlugin
 {
     interface Result
     {

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/LoadBalancingResult.java

@@ -23,10 +23,10 @@
 import java.util.Objects;
 
 /**
- * The outcome of applying a load balancing strategy, which will be used by client
+ * The outcome of applying a load balancing plugin, which will be used by client
  * software for scheduling work at the endpoints.
  */
-public class LoadBalancingResult implements LoadBalancingStrategy.Result
+public class LoadBalancingResult implements LoadBalancingPlugin.Result
 {
     private final List<Endpoint> routeEndpoints;
     private final List<Endpoint> writeEndpoints;

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/strategy/AllServersStrategy.java → enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/plugins/AllServersPlugin.java

@@ -17,7 +17,7 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
-package org.neo4j.causalclustering.load_balancing.strategy;
+package org.neo4j.causalclustering.load_balancing.plugins;
 
 import java.util.List;
 import java.util.Map;
@@ -33,7 +33,7 @@
 import org.neo4j.causalclustering.identity.MemberId;
 import org.neo4j.causalclustering.load_balancing.Endpoint;
 import org.neo4j.causalclustering.load_balancing.LoadBalancingResult;
-import org.neo4j.causalclustering.load_balancing.LoadBalancingStrategy;
+import org.neo4j.causalclustering.load_balancing.LoadBalancingPlugin;
 import org.neo4j.kernel.configuration.Config;
 
 import static java.util.Collections.emptyList;
@@ -42,15 +42,15 @@
 import static org.neo4j.causalclustering.load_balancing.Util.asList;
 
 /**
- * This is just a simple strategy and not intended for actual use. Will be replaced.
+ * This is just a simple plugin and not intended for actual use. Will be replaced.
  */
-public class AllServersStrategy implements LoadBalancingStrategy
+public class AllServersPlugin implements LoadBalancingPlugin
 {
     private final CoreTopologyService topologyService;
     private final LeaderLocator leaderLocator;
     private final Long timeToLive;
 
-    public AllServersStrategy( CoreTopologyService topologyService, LeaderLocator leaderLocator, Config config )
+    public AllServersPlugin( CoreTopologyService topologyService, LeaderLocator leaderLocator, Config config )
     {
         this.topologyService = topologyService;
         this.leaderLocator = leaderLocator;

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/strategy/ServerShufflingStrategy.java → enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/plugins/ServerShufflingPlugin.java

@@ -17,24 +17,24 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
-package org.neo4j.causalclustering.load_balancing.strategy;
+package org.neo4j.causalclustering.load_balancing.plugins;
 
 import java.util.Collections;
 import java.util.Map;
 
-import org.neo4j.causalclustering.load_balancing.LoadBalancingStrategy;
+import org.neo4j.causalclustering.load_balancing.LoadBalancingPlugin;
 
 /**
  * Shuffles the servers of the delegate around so that every client
  * invocation gets a a little bit of that extra entropy spice.
  *
  * N.B: Lists are shuffled in place.
  */
-public class ServerShufflingStrategy implements LoadBalancingStrategy
+public class ServerShufflingPlugin implements LoadBalancingPlugin
 {
-    private final LoadBalancingStrategy delegate;
+    private final LoadBalancingPlugin delegate;
 
-    public ServerShufflingStrategy( LoadBalancingStrategy delegate )
+    public ServerShufflingPlugin( LoadBalancingPlugin delegate )
     {
         this.delegate = delegate;
     }

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/strategy/server_policy/AnyTagFilter.java → enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/plugins/server_policies/AnyTagFilter.java

@@ -17,7 +17,7 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
-package org.neo4j.causalclustering.load_balancing.strategy.server_policy;
+package org.neo4j.causalclustering.load_balancing.plugins.server_policies;
 
 import java.util.Objects;
 import java.util.Set;

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/strategy/server_policy/FilterConfigParser.java → enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/plugins/server_policies/FilterConfigParser.java

@@ -17,7 +17,7 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
-package org.neo4j.causalclustering.load_balancing.strategy.server_policy;
+package org.neo4j.causalclustering.load_balancing.plugins.server_policies;
 
 import java.util.ArrayList;
 import java.util.Arrays;

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/strategy/server_policy/FilteringPolicy.java → enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/plugins/server_policies/FilteringPolicy.java

@@ -17,7 +17,7 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
-package org.neo4j.causalclustering.load_balancing.strategy.server_policy;
+package org.neo4j.causalclustering.load_balancing.plugins.server_policies;
 
 import java.util.Objects;
 import java.util.Set;

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/strategy/server_policy/FilteringPolicyLoader.java → enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/plugins/server_policies/FilteringPolicyLoader.java

@@ -17,7 +17,7 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
-package org.neo4j.causalclustering.load_balancing.strategy.server_policy;
+package org.neo4j.causalclustering.load_balancing.plugins.server_policies;
 
 import java.util.Map;
 import java.util.Set;
@@ -31,15 +31,15 @@
 import static org.neo4j.causalclustering.core.CausalClusteringSettings.load_balancing_config;
 
 /**
- * Loads filters under the name space of [...]config.strategy.policy_name
+ * Loads filters under the name space of a particular plugin.
  */
 class FilteringPolicyLoader
 {
-    static Policies load( Config config, String strategyName, LogProvider logProvider ) throws InvalidFilterSpecification
+    static Policies load( Config config, String pluginName, LogProvider logProvider ) throws InvalidFilterSpecification
     {
         Policies policies = new Policies( logProvider );
 
-        String prefix = policyPrefix( strategyName );
+        String prefix = policyPrefix( pluginName );
         Map<String,String> rawConfig = config.getRaw();
 
         Set<String> configKeys = rawConfig.keySet().stream()
@@ -58,8 +58,8 @@ static Policies load( Config config, String strategyName, LogProvider logProvide
         return policies;
     }
 
-    private static String policyPrefix( String strategyName )
+    private static String policyPrefix( String pluginName )
     {
-        return format( "%s.%s.", load_balancing_config.name(), strategyName );
+        return format( "%s.%s.", load_balancing_config.name(), pluginName );
     }
 }

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/strategy/server_policy/InvalidFilterSpecification.java → enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/plugins/server_policies/InvalidFilterSpecification.java

@@ -17,9 +17,9 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
-package org.neo4j.causalclustering.load_balancing.strategy.server_policy;
+package org.neo4j.causalclustering.load_balancing.plugins.server_policies;
 
-class InvalidFilterSpecification extends Exception
+public class InvalidFilterSpecification extends Exception
 {
     InvalidFilterSpecification( String message )
     {

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/strategy/server_policy/Policies.java → enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/plugins/server_policies/Policies.java

@@ -17,7 +17,7 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
-package org.neo4j.causalclustering.load_balancing.strategy.server_policy;
+package org.neo4j.causalclustering.load_balancing.plugins.server_policies;
 
 import java.util.HashMap;
 import java.util.Map;
@@ -31,9 +31,11 @@
 class Policies
 {
     static final String POLICY_KEY = "load_balancing.policy"; // TODO: move somewhere (driver support package?)
+    static final String DEFAULT_POLICY_NAME = "default";
+    static final Policy DEFAULT_POLICY = new FilteringPolicy( IdentityFilter.as() );
 
     private final Map<String,Policy> policies = new HashMap<>();
-    private final Policy DEFAULT_POLICY = new FilteringPolicy( IdentityFilter.as() );
+
     private final Log log;
 
     Policies( LogProvider logProvider )
@@ -53,15 +55,13 @@ void addPolicy( String policyName, Policy policy )
     Policy selectFor( Map<String,String> context )
     {
         String policyName = context.get( POLICY_KEY );
+        policyName = (policyName != null) ? policyName : DEFAULT_POLICY_NAME;
+
         Policy selectedPolicy = policies.get( policyName );
 
-        if ( policyName == null )
-        {
-            return DEFAULT_POLICY;
-        }
-        else if ( selectedPolicy == null )
+        if ( selectedPolicy == null )
         {
-            log.warn( format( "Policy '%s' could not be found. Will use default instead.", policyName ) );
+            log.warn( format( "Policy definition for '%s' could not be found. Will use built-in default instead.", policyName ) );
             return DEFAULT_POLICY;
         }
         else

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/strategy/server_policy/Policy.java → enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/plugins/server_policies/Policy.java

@@ -17,7 +17,7 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
-package org.neo4j.causalclustering.load_balancing.strategy.server_policy;
+package org.neo4j.causalclustering.load_balancing.plugins.server_policies;
 
 import java.util.Set;
 

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/strategy/server_policy/ServerInfo.java → enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/plugins/server_policies/ServerInfo.java

@@ -17,7 +17,7 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
-package org.neo4j.causalclustering.load_balancing.strategy.server_policy;
+package org.neo4j.causalclustering.load_balancing.plugins.server_policies;
 
 import java.util.Objects;
 import java.util.Set;

enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/strategy/server_policy/ServerPolicyStrategy.java → enterprise/causal-clustering/src/main/java/org/neo4j/causalclustering/load_balancing/plugins/server_policies/ServerPoliciesPlugin.java

@@ -17,7 +17,7 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
-package org.neo4j.causalclustering.load_balancing.strategy.server_policy;
+package org.neo4j.causalclustering.load_balancing.plugins.server_policies;
 
 import java.util.List;
 import java.util.Map;
@@ -33,39 +33,40 @@
 import org.neo4j.causalclustering.discovery.TopologyService;
 import org.neo4j.causalclustering.identity.MemberId;
 import org.neo4j.causalclustering.load_balancing.Endpoint;
+import org.neo4j.causalclustering.load_balancing.LoadBalancingPlugin;
 import org.neo4j.causalclustering.load_balancing.LoadBalancingResult;
-import org.neo4j.causalclustering.load_balancing.LoadBalancingStrategy;
 import org.neo4j.kernel.configuration.Config;
 import org.neo4j.logging.LogProvider;
 
 import static java.util.Collections.emptyList;
 import static org.neo4j.causalclustering.load_balancing.Util.asList;
 import static org.neo4j.causalclustering.load_balancing.Util.extractBoltAddress;
+import static org.neo4j.causalclustering.load_balancing.plugins.server_policies.FilteringPolicyLoader.load;
 
 /**
- * The server policy strategy defines policies on the server-side which
+ * The server policies plugin defines policies on the server-side which
  * can be bound to by a client by supplying a appropriately formed context.
  *
- * An example would be to define a policy for a particular region.
+ * An example would be to define different policies for different regions.
  */
-public class ServerPolicyStrategy implements LoadBalancingStrategy
+public class ServerPoliciesPlugin implements LoadBalancingPlugin
 {
-    private static final String STRATEGY_NAME = "server_policy";
+    private static final String PLUGIN_NAME = "server_policies";
 
     private final TopologyService topologyService;
     private final LeaderLocator leaderLocator;
     private final Long timeToLive;
     private final boolean allowReadsOnFollowers;
     private final Policies policies;
 
-    public ServerPolicyStrategy( TopologyService topologyService, LeaderLocator leaderLocator,
+    public ServerPoliciesPlugin( TopologyService topologyService, LeaderLocator leaderLocator,
             LogProvider logProvider, Config config ) throws InvalidFilterSpecification
     {
         this.topologyService = topologyService;
         this.leaderLocator = leaderLocator;
         this.timeToLive = config.get( CausalClusteringSettings.cluster_routing_ttl );
         this.allowReadsOnFollowers = config.get( CausalClusteringSettings.cluster_allow_reads_on_followers );
-        this.policies = FilteringPolicyLoader.load( config, STRATEGY_NAME, logProvider );
+        this.policies = load( config, PLUGIN_NAME, logProvider );
     }
 
     @Override