diff --git a/moto/server.py b/moto/server.py
index 971589ca..89be4709 100644
--- a/moto/server.py
+++ b/moto/server.py
@@ -58,9 +58,7 @@ class DomainDispatcherApplication(object):
                 if re.match(url_base, 'http://%s' % host):
                     return backend_name
 
-        raise RuntimeError('Invalid host: "%s"' % host)
-
-    def infer_service_region(self, environ):
+    def infer_service_region_host(self, environ):
         auth = environ.get('HTTP_AUTHORIZATION')
         if auth:
             # Signed request
@@ -70,21 +68,35 @@ class DomainDispatcherApplication(object):
             try:
                 credential_scope = auth.split(",")[0].split()[1]
                 _, _, region, service, _ = credential_scope.split("/")
-                return service, region
             except ValueError:
                 # Signature format does not match, this is exceptional and we can't
                 # infer a service-region. A reduced set of services still use
                 # the deprecated SigV2, ergo prefer S3 as most likely default.
                 # https://docs.aws.amazon.com/general/latest/gr/signature-version-2.html
-                return DEFAULT_SERVICE_REGION
+                service, region = DEFAULT_SERVICE_REGION
         else:
             # Unsigned request
             target = environ.get('HTTP_X_AMZ_TARGET')
             if target:
                 service, _ = target.split('.', 1)
-                return UNSIGNED_REQUESTS.get(service, DEFAULT_SERVICE_REGION)
-            # S3 is the last resort when the target is also unknown
-            return DEFAULT_SERVICE_REGION
+                service, region = UNSIGNED_REQUESTS.get(service, DEFAULT_SERVICE_REGION)
+            else:
+                # S3 is the last resort when the target is also unknown
+                service, region = DEFAULT_SERVICE_REGION
+
+        if service == 'dynamodb':
+            if environ['HTTP_X_AMZ_TARGET'].startswith('DynamoDBStreams'):
+                host = 'dynamodbstreams'
+            else:
+                dynamo_api_version = environ['HTTP_X_AMZ_TARGET'].split("_")[1].split(".")[0]
+                # If Newer API version, use dynamodb2
+                if dynamo_api_version > "20111205":
+                    host = "dynamodb2"
+        else:
+            host = "{service}.{region}.amazonaws.com".format(
+                service=service, region=region)
+
+        return host
 
     def get_application(self, environ):
         path_info = environ.get('PATH_INFO', '')
@@ -101,22 +113,14 @@ class DomainDispatcherApplication(object):
             host = "instance_metadata"
         else:
             host = environ['HTTP_HOST'].split(':')[0]
-        if host in {'localhost', 'motoserver'} or host.startswith("192.168."):
-            service, region = self.infer_service_region(environ)
-            if service == 'dynamodb':
-                if environ['HTTP_X_AMZ_TARGET'].startswith('DynamoDBStreams'):
-                    host = 'dynamodbstreams'
-                else:
-                    dynamo_api_version = environ['HTTP_X_AMZ_TARGET'].split("_")[1].split(".")[0]
-                    # If Newer API version, use dynamodb2
-                    if dynamo_api_version > "20111205":
-                        host = "dynamodb2"
-            else:
-                host = "{service}.{region}.amazonaws.com".format(
-                    service=service, region=region)
 
         with self.lock:
             backend = self.get_backend_for_host(host)
+            if not backend:
+                # No regular backend found; try parsing other headers
+                host = self.infer_service_region_host(environ)
+                backend = self.get_backend_for_host(host)
+
             app = self.app_instances.get(backend, None)
             if app is None:
                 app = self.create_app(backend)
diff --git a/tests/test_core/test_server.py b/tests/test_core/test_server.py
index b7290e35..bd00b17c 100644
--- a/tests/test_core/test_server.py
+++ b/tests/test_core/test_server.py
@@ -38,12 +38,6 @@ def test_domain_dispatched():
     keys[0].should.equal('EmailResponse.dispatch')
 
 
-def test_domain_without_matches():
-    dispatcher = DomainDispatcherApplication(create_backend_app)
-    dispatcher.get_application.when.called_with(
-        {"HTTP_HOST": "not-matching-anything.com"}).should.throw(RuntimeError)
-
-
 def test_domain_dispatched_with_service():
     # If we pass a particular service, always return that.
     dispatcher = DomainDispatcherApplication(create_backend_app, service="s3")