diff --git a/server/src/main/java/com/cloud/resource/ResourceManagerImpl.java b/server/src/main/java/com/cloud/resource/ResourceManagerImpl.java
index 00e9cec90d8..26532354720 100755
--- a/server/src/main/java/com/cloud/resource/ResourceManagerImpl.java
+++ b/server/src/main/java/com/cloud/resource/ResourceManagerImpl.java
@@ -42,16 +42,6 @@ import java.util.stream.Collectors;
 import javax.inject.Inject;
 import javax.naming.ConfigurationException;
 
-import com.cloud.gpu.dao.VgpuProfileDao;
-import com.cloud.offering.ServiceOffering;
-import com.cloud.service.ServiceOfferingDetailsVO;
-import com.cloud.storage.ScopeType;
-import com.cloud.storage.StoragePoolAndAccessGroupMapVO;
-import com.cloud.storage.dao.StoragePoolAndAccessGroupMapDao;
-import com.cloud.storage.dao.StoragePoolTagsDao;
-import com.cloud.gpu.GpuCardVO;
-import com.cloud.gpu.VgpuProfileVO;
-import com.cloud.gpu.dao.GpuCardDao;
 import org.apache.cloudstack.alert.AlertService;
 import org.apache.cloudstack.annotation.AnnotationService;
 import org.apache.cloudstack.annotation.dao.AnnotationDao;
@@ -154,10 +144,14 @@ import com.cloud.exception.ResourceUnavailableException;
 import com.cloud.exception.StorageConflictException;
 import com.cloud.exception.StorageUnavailableException;
 import com.cloud.gpu.GPU;
+import com.cloud.gpu.GpuCardVO;
 import com.cloud.gpu.HostGpuGroupsVO;
 import com.cloud.gpu.VGPUTypesVO;
+import com.cloud.gpu.VgpuProfileVO;
+import com.cloud.gpu.dao.GpuCardDao;
 import com.cloud.gpu.dao.HostGpuGroupsDao;
 import com.cloud.gpu.dao.VGPUTypesDao;
+import com.cloud.gpu.dao.VgpuProfileDao;
 import com.cloud.ha.HighAvailabilityManager;
 import com.cloud.ha.HighAvailabilityManager.WorkType;
 import com.cloud.ha.HighAvailabilityManagerImpl;
@@ -178,17 +172,21 @@ import com.cloud.hypervisor.HypervisorGuru;
 import com.cloud.hypervisor.kvm.discoverer.KvmDummyResourceBase;
 import com.cloud.network.dao.IPAddressDao;
 import com.cloud.network.dao.IPAddressVO;
+import com.cloud.offering.ServiceOffering;
 import com.cloud.org.Cluster;
 import com.cloud.org.Grouping;
 import com.cloud.org.Managed;
 import com.cloud.serializer.GsonHelper;
 import com.cloud.server.ManagementService;
+import com.cloud.service.ServiceOfferingDetailsVO;
 import com.cloud.service.ServiceOfferingVO;
 import com.cloud.service.dao.ServiceOfferingDao;
 import com.cloud.service.dao.ServiceOfferingDetailsDao;
 import com.cloud.storage.GuestOSCategoryVO;
+import com.cloud.storage.ScopeType;
 import com.cloud.storage.StorageManager;
 import com.cloud.storage.StoragePool;
+import com.cloud.storage.StoragePoolAndAccessGroupMapVO;
 import com.cloud.storage.StoragePoolHostVO;
 import com.cloud.storage.StoragePoolStatus;
 import com.cloud.storage.StorageService;
@@ -196,7 +194,9 @@ import com.cloud.storage.VMTemplateVO;
 import com.cloud.storage.Volume;
 import com.cloud.storage.VolumeVO;
 import com.cloud.storage.dao.GuestOSCategoryDao;
+import com.cloud.storage.dao.StoragePoolAndAccessGroupMapDao;
 import com.cloud.storage.dao.StoragePoolHostDao;
+import com.cloud.storage.dao.StoragePoolTagsDao;
 import com.cloud.storage.dao.VMTemplateDao;
 import com.cloud.storage.dao.VolumeDao;
 import com.cloud.user.Account;
@@ -719,6 +719,7 @@ public class ResourceManagerImpl extends ManagerBase implements ResourceManager,
         String hypervisorType =
                 cmd.getHypervisor().equalsIgnoreCase(HypervisorGuru.HypervisorCustomDisplayName.value()) ?
                 "Custom" : cmd.getHypervisor();
+        checkForDuplicateHost(url);
         return discoverHostsFull(dcId, podId, clusterId, clusterName, url, username, password, hypervisorType,
                 hostTags, storageAccessGroups, cmd.getFullUrlParams(), false, cmd.getExternalDetails());
     }
@@ -3523,6 +3524,32 @@ public class ResourceManagerImpl extends ManagerBase implements ResourceManager,
         return host;
     }
 
+    void checkForDuplicateHost(final String url) {
+        String hostIpOrName = null;
+        String ipAddress = null;
+        try {
+            hostIpOrName = new URI(UriUtils.encodeURIComponent(url)).getHost();
+            if (StringUtils.isBlank(hostIpOrName)) {
+                return;
+            }
+            InetAddress ip = InetAddress.getByName(hostIpOrName);
+            ipAddress = ip.getHostAddress();
+        } catch (final URISyntaxException | UnknownHostException ignore) {
+            // unparseable URL or unknown host - discoverer will reject it shortly anyway
+            return;
+        }
+
+        if (StringUtils.isNotBlank(ipAddress)) {
+            final HostVO existingByIp = _hostDao.findByIp(ipAddress);
+            // findByIp matches hosts of any type; only a Routing host is a duplicate for addHost
+            if (existingByIp != null && Host.Type.Routing.equals(existingByIp.getType())) {
+                throw new InvalidParameterValueException(String.format(
+                        "A host with IP address '%s' (%s) already exists (id: %s). Remove it before adding again.",
+                        ipAddress, hostIpOrName, existingByIp.getUuid()));
+            }
+        }
+    }
+
     private Host createHostAndAgentDeferred(final ServerResource resource, final Map<String, String> details, final boolean old, final List<String> hostTags, List<String> storageAccessGroups, final boolean forRebalance) {
         HostVO host = null;
         StartupCommand[] cmds = null;
diff --git a/server/src/main/java/com/cloud/template/TemplateManagerImpl.java b/server/src/main/java/com/cloud/template/TemplateManagerImpl.java
index 39870ebaafd..13c47e83bfc 100755
--- a/server/src/main/java/com/cloud/template/TemplateManagerImpl.java
+++ b/server/src/main/java/com/cloud/template/TemplateManagerImpl.java
@@ -322,6 +322,8 @@ public class TemplateManagerImpl extends ManagerBase implements TemplateManager,
     private SecondaryStorageHeuristicDao secondaryStorageHeuristicDao;
     @Inject
     private HeuristicRuleHelper heuristicRuleHelper;
+    @Inject
+    private UserDataDao userDataDao;
 
     private List<TemplateAdapter> _adapters;
 
@@ -329,12 +331,6 @@ public class TemplateManagerImpl extends ManagerBase implements TemplateManager,
 
     protected boolean backupSnapshotAfterTakingSnapshot = SnapshotInfo.BackupSnapshotAfterTakingSnapshot.value();
 
-    @Inject
-    private UserDataDao userDataDao;
-
-    @Inject
-    private UserDataDao userDataDao;
-
     private TemplateAdapter getAdapter(HypervisorType type) {
         TemplateAdapter adapter = null;
         if (type == HypervisorType.BareMetal) {
diff --git a/server/src/main/java/com/cloud/user/AccountManagerImpl.java b/server/src/main/java/com/cloud/user/AccountManagerImpl.java
index a09b8b329f4..b4c23beaef2 100644
--- a/server/src/main/java/com/cloud/user/AccountManagerImpl.java
+++ b/server/src/main/java/com/cloud/user/AccountManagerImpl.java
@@ -42,8 +42,8 @@ import javax.crypto.spec.SecretKeySpec;
 import javax.inject.Inject;
 import javax.naming.ConfigurationException;
 
-import org.apache.cloudstack.acl.APIChecker;
 import org.apache.cloudstack.acl.APIAclChecker;
+import org.apache.cloudstack.acl.APIChecker;
 import org.apache.cloudstack.acl.ControlledEntity;
 import org.apache.cloudstack.acl.InfrastructureEntity;
 import org.apache.cloudstack.acl.QuerySelector;
@@ -176,10 +176,9 @@ import com.cloud.user.dao.UserDataDao;
 import com.cloud.utils.ConstantTimeComparator;
 import com.cloud.utils.NumbersUtil;
 import com.cloud.utils.Pair;
-import com.cloud.utils.Ternary;
-import com.cloud.utils.UuidUtils;
 import com.cloud.utils.StringUtils;
 import com.cloud.utils.Ternary;
+import com.cloud.utils.UuidUtils;
 import com.cloud.utils.component.ComponentContext;
 import com.cloud.utils.component.Manager;
 import com.cloud.utils.component.ManagerBase;