Fixes issue where multiple instances of ApplicaitonLifecycle are created.

KubernetesWorkflow/ApplicationLifecycle.cs

@@ -4,6 +4,7 @@ namespace KubernetesWorkflow
 {
     public class ApplicationLifecycle
     {
+        private static object instanceLock = new object();
         private static ApplicationLifecycle? instance;
         private readonly NumberSource servicePortNumberSource = new NumberSource(30001);
         private readonly NumberSource namespaceNumberSource = new NumberSource(0);
@@ -17,11 +18,14 @@ namespace KubernetesWorkflow
             // I know singletons are quite evil. But we need to be sure this object is created only once
             // and persists for the entire application lifecycle.
             get
+            {
+                lock (instanceLock)
                 {
                     if (instance == null) instance = new ApplicationLifecycle();
                     return instance;
                 }
             }
+        }
 
         public NumberSource GetServiceNumberSource()
         {