Force hosts to have at least one character

test/v2.7/backend.json

@@ -0,0 +1,87 @@
+{
+    "description": "Backend object test",
+    "target": "https://www.krakend.io/schema/v2.7/backend.json",
+    "tests": [
+        {
+            "description": "Simple backend declaration with no host",
+            "data": {
+                "url_pattern": "/__debug/root"
+            },
+            "valid": true
+        },
+        {
+            "description": "Simple backend declaration with host",
+            "data": {
+                "url_pattern": "/__debug/root",
+                "host": [
+                    "amqp://blah"
+                ]
+            },
+            "valid": true
+        },
+        {
+            "description": "Simple backend declaration with empty string host",
+            "data": {
+                "url_pattern": "/__debug/root",
+                "host": [
+                    ""
+                ]
+            },
+            "valid": false
+        },
+        {
+            "description": "Simple backend declaration with no pattern",
+            "data": {
+                "host": [
+                    "http://foo"
+                ]
+            },
+            "valid": false
+        },
+        {
+            "description": "Backend declaration with a few components",
+            "data": {
+                "host": [
+                    "http://127.0.0.1:8080"
+                ],
+                "input_headers": [
+                    "Accept"
+                ],
+                "url_pattern": "/__debug/",
+                "extra_config": {
+                    "auth/ntlm": {
+                        "user": "user",
+                        "password": "pass"
+                    },
+                    "auth/gcp": {
+                        "audience": "https://gcptest-76fewi6rca-uc.a.run.app",
+                        "credentials_file": "/etc/krakend/gcp.json",
+                        "custom_claims": {
+                            "a": 1
+                        }
+                    },
+                    "backend/http": {
+                        "return_error_code": true,
+                        "@extra_comment": "here"
+                    },
+                    "backend/soap": {
+                        "path": "./path/to.xml",
+                        "content_type": "application/xml",
+                        "debug": false
+                    },
+                    "modifier/body-generator": {
+                        "content_type": "application/json",
+                        "debug": false,
+                        "template": "abcdef"
+                    },
+                    "modifier/response-body-generator": {
+                        "content_type": "application/json",
+                        "debug": false,
+                        "template": "abcdef"
+                    }
+                }
+            },
+            "valid": true
+        }
+    ]
+}

v2.7/backend.json

@@ -74,7 +74,11 @@
       "$id": "#backend/host",
       "title": "Host array",
       "description": "An array with all the available hosts to [load balance](https://www.krakend.io/docs/throttling/load-balancing/#balancing-egress-traffic-to-upstream) requests, including the schema (when possible) `schema://host:port`. E.g.: ` https://my.users-ms.com`. If you are in a platform where hosts or services are balanced (e.g., a K8S service), write a single entry in the array with the service name/balancer address. Defaults to the `host` declaration at the configuration's root level, and the service fails starting when there is none.",
-      "type": "array"
+      "type": "array",
+      "items": {
+        "type": "string",
+        "minLength": 1
+      }
     },
     "input_headers": {
       "$id": "#backend/input_headers",

v2.7/krakend.json

@@ -1418,7 +1418,11 @@
         "host": {
           "title": "Host array",
           "description": "An array with all the available hosts to [load balance](https://www.krakend.io/docs/throttling/load-balancing/#balancing-egress-traffic-to-upstream) requests, including the schema (when possible) `schema://host:port`. E.g.: ` https://my.users-ms.com`. If you are in a platform where hosts or services are balanced (e.g., a K8S service), write a single entry in the array with the service name/balancer address. Defaults to the `host` declaration at the configuration's root level, and the service fails starting when there is none.",
-          "type": "array"
+          "type": "array",
+          "items": {
+            "type": "string",
+            "minLength": 1
+          }
         },
         "input_headers": {
           "title": "Allowed Headers In",