Development: Fix Hazelcast client mode for build agents

Fixes several issues with the Hazelcast client mode implementation:

1. IPv6 address formatting: Core node addresses are now correctly
   formatted as [ipv6address]:port instead of ipv6address:port

2. Async startup: Build agents now always start asynchronously and
   connect to the cluster in the background, preventing startup
   blocking when core nodes are temporarily unavailable

3. Client address resolution: HazelcastDistributedDataProviderService
   now correctly handles Hazelcast clients by using getLocalEndpoint()
   instead of getLocalMember() which only works for cluster members

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: krusche

src/main/java/de/tum/cit/aet/artemis/core/config/CacheConfiguration.java

@@ -401,12 +401,11 @@ private HazelcastInstance createHazelcastClient() {
         }
 
         // Connection strategy configuration for resilience:
-        // - asyncStart=true: Don't block startup if no core nodes available yet
+        // - asyncStart=true: Don't block startup, connect in background
         // - reconnectMode=ON: Automatically reconnect if connection is lost
         // This allows build agents to start even when core nodes are temporarily unavailable
         // and reconnect automatically when they become available.
-        boolean hasInitialAddresses = !discoveredAddresses.isEmpty();
-        clientConfig.getConnectionStrategyConfig().setAsyncStart(!hasInitialAddresses)  // Block only if we have addresses to connect to
+        clientConfig.getConnectionStrategyConfig().setAsyncStart(true)  // Never block startup - connect in background
                 .setReconnectMode(ClientConnectionStrategyConfig.ReconnectMode.ON);
 
         // Connection retry configuration - aggressive retry to handle temporary core node unavailability
@@ -426,11 +425,11 @@ private HazelcastInstance createHazelcastClient() {
         // Mark this instance as a client in the service registry
         hazelcastConnection.registerAsClient();
 
-        if (hasInitialAddresses) {
+        if (!discoveredAddresses.isEmpty()) {
             log.info("Creating Hazelcast client to connect to core cluster at: {}", discoveredAddresses);
         }
         else {
-            log.warn("No core nodes found in service registry. Hazelcast client will start asynchronously and retry connection.");
+            log.warn("No core nodes found in service registry. Hazelcast client will retry connection in background.");
         }
 
         return HazelcastClient.newHazelcastClient(clientConfig);

src/main/java/de/tum/cit/aet/artemis/core/config/HazelcastConnection.java

@@ -286,13 +286,20 @@ private boolean isCurrentInstance(ServiceInstance instance) {
 
     /**
      * Formats a service instance address as "host:port" for Hazelcast connection.
+     * For IPv6 addresses, the format is "[ipv6address]:port".
      *
      * @param instance the service instance
      * @return the formatted address string
      */
     private String formatInstanceAddress(ServiceInstance instance) {
-        String host = instance.getHost().replace("[", "").replace("]", ""); // Handle IPv6 brackets
+        String host = instance.getHost().replace("[", "").replace("]", ""); // Remove any existing brackets
         String port = instance.getMetadata().getOrDefault("hazelcast.port", String.valueOf(hazelcastPort));
+
+        // Check if this is an IPv6 address (contains colons)
+        if (host.contains(":")) {
+            // IPv6 addresses must be wrapped in brackets before the port
+            return "[" + host + "]:" + port;
+        }
         return host + ":" + port;
     }
 

src/main/java/de/tum/cit/aet/artemis/programming/service/localci/distributed/hazelcast/HazelcastDistributedDataProviderService.java

@@ -1,5 +1,6 @@
 package de.tum.cit.aet.artemis.programming.service.localci.distributed.hazelcast;
 
+import java.net.InetSocketAddress;
 import java.util.ArrayList;
 import java.util.Set;
 import java.util.stream.Collectors;
@@ -9,6 +10,7 @@
 import org.springframework.context.annotation.Lazy;
 import org.springframework.stereotype.Service;
 
+import com.hazelcast.client.impl.clientside.HazelcastClientProxy;
 import com.hazelcast.cluster.Member;
 import com.hazelcast.core.HazelcastInstance;
 import com.hazelcast.core.HazelcastInstanceNotActiveException;
@@ -68,13 +70,27 @@ public boolean isInstanceRunning() {
     }
 
     /**
-     * @return the address of the local Hazelcast member
+     * Returns the address of the local Hazelcast instance.
+     * For cluster members, returns the member's cluster address.
+     * For clients (e.g., build agents in client mode), returns the client's local endpoint address.
+     *
+     * @return the address as a string in the format "[host]:port"
      */
     @Override
     public String getLocalMemberAddress() {
         if (!isInstanceRunning()) {
             throw new HazelcastInstanceNotActiveException();
         }
+
+        // Check if this is a Hazelcast client (build agents in client mode)
+        if (hazelcastInstance instanceof HazelcastClientProxy) {
+            // For clients, use getLocalEndpoint() which provides the client's socket address
+            InetSocketAddress socketAddress = (InetSocketAddress) hazelcastInstance.getLocalEndpoint().getSocketAddress();
+            // Format consistently with cluster member addresses: [host]:port
+            return "[" + socketAddress.getAddress().getHostAddress() + "]:" + socketAddress.getPort();
+        }
+
+        // For cluster members, use the traditional approach
         return hazelcastInstance.getCluster().getLocalMember().getAddress().toString();
     }