feat: assign channels to servers (#531)

spec/asyncapi.md

@@ -563,6 +563,7 @@ Field Name | Type | Description
 ---|:---:|---
 <a name="channelItemObjectRef"></a>$ref | `string` | Allows for an external definition of this channel item. The referenced structure MUST be in the format of a [Channel Item Object](#channelItemObject). If there are conflicts between the referenced definition and this Channel Item's definition, the behavior is *undefined*.
 <a name="channelItemObjectDescription"></a>description | `string` | An optional description of this channel item. [CommonMark syntax](https://spec.commonmark.org/) can be used for rich text representation.
+<a name="channelItemObjectServers"></a>servers | [`string`] | The servers on which this channel is available, specified as an optional unordered list of names (string keys) of [Server Objects](#serverObject) defined in the [Servers Object](#serversObject) (a map). If `servers` is absent or empty then this channel must be available on all servers defined in the [Servers Object](#serversObject).
 <a name="channelItemObjectSubscribe"></a>subscribe | [Operation Object](#operationObject) | A definition of the SUBSCRIBE operation, which defines the messages produced by the application and sent to the channel.
 <a name="channelItemObjectPublish"></a>publish | [Operation Object](#operationObject) | A definition of the PUBLISH operation, which defines the messages consumed by the application from the channel.
 <a name="channelItemObjectParameters"></a>parameters | [Parameters Object](#parametersObject) | A map of the parameters included in the channel name. It SHOULD be present only when using channels with expressions (as defined by [RFC 6570 section 2.2](https://tools.ietf.org/html/rfc6570#section-2.2)).
@@ -646,6 +647,40 @@ subscribe:
 ```
 
 
+Using explicit by-name references to the servers on which the channel is available:
+
+```json
+{
+  "description": "This application publishes WebUICommand messages to an AMQP queue on RabbitMQ brokers in the Staging and Production environments.",
+  "servers": [
+    "rabbitmqBrokerInProd",
+    "rabbitmqBrokerInStaging",
+  ],
+  "subscribe": {
+    "message": {
+      "$ref": "#/components/messages/WebUICommand"
+    }
+  },
+  "bindings": {
+    "amqp": {
+      "is": "queue"
+    }
+  }
+}
+```
+
+```yaml
+description: This application publishes WebUICommand messages to an AMQP queue on RabbitMQ brokers in the Staging and Production environments.
+servers:
+  - rabbitmqBrokerInProd
+  - rabbitmqBrokerInStaging
+subscribe:
+  message:
+    $ref: "#/components/messages/WebUICommand"
+bindings:
+  amqp:
+    is: queue
+```