OWLS-103825: Available should be true for admin server only domain

operator/src/main/java/oracle/kubernetes/operator/DomainStatusUpdater.java

@@ -857,13 +857,23 @@ private Collection<DomainPresenceInfo.ServerStartupInfo> getServerStartupInfos()
 
         // when the domain start policy is ADMIN_ONLY, the admin server is considered to be an application server.
         private boolean isApplicationServer(String serverName) {
-          return isAdminOnlyDomain() || !isAdminServer(serverName);
+          return !isAdminServer(serverName);
         }
 
         private boolean isAdminOnlyDomain() {
+          return isAdminOnlyServerStartPolicy()
+                  || isOnlyAdminServerRunningInDomain();
+        }
+
+        private boolean isAdminOnlyServerStartPolicy() {
           return getDomain().getSpec().getServerStartPolicy() == ServerStartPolicy.ADMIN_ONLY;
         }
 
+        private boolean isOnlyAdminServerRunningInDomain() {
+          return status.getServers().size() == 1
+                  && status.getServers().get(0).getServerName().equals(getInfo().getAdminServerName());
+        }
+
         private boolean isAdminServer(String serverName) {
           return status.getServers().stream()
               .filter(s -> s.getServerName().equals(serverName))

operator/src/test/java/oracle/kubernetes/operator/DomainStatusUpdateTestBase.java

@@ -1736,6 +1736,16 @@ void whenServerStartupInfoIsNull_availableIsFalse() {
         hasItems(new ClusterCondition(ClusterConditionType.AVAILABLE).withStatus(FALSE)));
   }
 
+  @Test
+  void whenDomainOnlyHasAdminServer_availableIsTrue() {
+    configureDomain().configureAdminServer();
+    defineScenario().build();
+
+    updateDomainStatus();
+
+    assertThat(getRecordedDomain(), hasCondition(AVAILABLE).withStatus(TRUE));
+  }
+
   private Collection<ClusterCondition> getClusterConditions() {
     return testSupport.<ClusterResource>getResourceWithName(KubernetesTestSupport.CLUSTER, "cluster1")
         .getStatus().getConditions();