- Only add topic mappings if running a primary instance

- Connection string has precedence over custom config

Author: SzymonPobiega

src/ServiceControl.Transports.ASBS/ASBSTransportCustomization.cs

@@ -10,8 +10,6 @@
 
     public class ASBSTransportCustomization : TransportCustomization<AzureServiceBusTransport>
     {
-        const string DefaultSingleTopic = "bundle-1";
-
         protected override void CustomizeTransportForPrimaryEndpoint(EndpointConfiguration endpointConfiguration, AzureServiceBusTransport transportDefinition, TransportSettings transportSettings) =>
             transportDefinition.TransportTransactionMode = TransportTransactionMode.SendsAtomicWithReceive;
 
@@ -24,21 +22,47 @@ protected override void CustomizeTransportForMonitoringEndpoint(EndpointConfigur
         protected override AzureServiceBusTransport CreateTransport(TransportSettings transportSettings, TransportTransactionMode preferredTransactionMode = TransportTransactionMode.ReceiveOnly)
         {
             var connectionSettings = ConnectionStringParser.Parse(transportSettings.ConnectionString);
-            TopicTopology selectedTopology;
 
-            var serviceBusRootNamespace = new SettingsRootNamespace("ServiceControl.Transport.ASBS");
-            if (SettingsReader.TryRead<string>(serviceBusRootNamespace, "Topology", out var topologyJson))
+            if (!transportSettings.TryGet(out TopicTopology selectedTopology))
             {
-                //Load topology from json
-                selectedTopology = TopicTopology.FromOptions(JsonSerializer.Deserialize<TopologyOptions>(topologyJson));
+                //Topology is pre-selected and customized only when creating transport for the primary instance
+                //For all other cases use the connection string to determine which topology to use
+                if (connectionSettings.TopicName != null)
+                {
+                    selectedTopology = TopicTopology.MigrateFromNamedSingleTopic(connectionSettings.TopicName);
+                }
+                else
+                {
+                    selectedTopology = TopicTopology.Default;
+                }
             }
-            else if (connectionSettings.TopicName != null)
+
+            var transport = connectionSettings.AuthenticationMethod.CreateTransportDefinition(connectionSettings, selectedTopology);
+            transport.UseWebSockets = connectionSettings.UseWebSockets;
+            transport.EnablePartitioning = connectionSettings.EnablePartitioning;
+
+            transport.TransportTransactionMode = transport.GetSupportedTransactionModes().Contains(preferredTransactionMode) ? preferredTransactionMode : TransportTransactionMode.ReceiveOnly;
+
+            return transport;
+        }
+
+        protected override void AddTransportForPrimaryCore(IServiceCollection services,
+            TransportSettings transportSettings)
+        {
+            services.AddSingleton<IBrokerThroughputQuery, AzureQuery>();
+
+            var connectionSettings = ConnectionStringParser.Parse(transportSettings.ConnectionString);
+            TopicTopology selectedTopology;
+
+            var serviceBusRootNamespace = new SettingsRootNamespace("ServiceControl.Transport.ASBS");
+            if (connectionSettings.TopicName != null)
             {
                 //Bundle name provided -> use migration topology
+                //Need to explicitly specific events to be published on the single topic
                 selectedTopology = TopicTopology.FromOptions(new MigrationTopologyOptions
                 {
-                    TopicToPublishTo = connectionSettings.TopicName ?? DefaultSingleTopic,
-                    TopicToSubscribeOn = connectionSettings.TopicName ?? DefaultSingleTopic,
+                    TopicToPublishTo = connectionSettings.TopicName,
+                    TopicToSubscribeOn = connectionSettings.TopicName,
                     EventsToMigrateMap = [
                         "ServiceControl.Contracts.CustomCheckFailed",
                         "ServiceControl.Contracts.CustomCheckSucceeded",
@@ -52,25 +76,18 @@ protected override AzureServiceBusTransport CreateTransport(TransportSettings tr
                     ]
                 });
             }
+            else if (SettingsReader.TryRead<string>(serviceBusRootNamespace, "Topology", out var topologyJson))
+            {
+                //Load topology from json
+                selectedTopology = TopicTopology.FromOptions(JsonSerializer.Deserialize(topologyJson, TopologyOptionsSerializationContext.Default.TopologyOptions));
+            }
             else
             {
                 //Default to topic-per-event topology
                 selectedTopology = TopicTopology.Default;
             }
 
-            var transport = connectionSettings.AuthenticationMethod.CreateTransportDefinition(connectionSettings, selectedTopology);
-            transport.UseWebSockets = connectionSettings.UseWebSockets;
-            transport.EnablePartitioning = connectionSettings.EnablePartitioning;
-
-            transport.TransportTransactionMode = transport.GetSupportedTransactionModes().Contains(preferredTransactionMode) ? preferredTransactionMode : TransportTransactionMode.ReceiveOnly;
-
-            return transport;
-        }
-
-        protected override void AddTransportForPrimaryCore(IServiceCollection services,
-            TransportSettings transportSettings)
-        {
-            services.AddSingleton<IBrokerThroughputQuery, AzureQuery>();
+            transportSettings.Set(selectedTopology);
         }
 
         protected override void AddTransportForMonitoringCore(IServiceCollection services, TransportSettings transportSettings)