document new publishRate trigger

Corresponding code change: kedacore/keda#1653

content/docs/2.2/scalers/rabbitmq-queue.md

@@ -17,7 +17,8 @@ triggers:
   metadata:
     host: amqp://localhost:5672/vhost # Optional. If not specified, it must be done by using TriggerAuthentication.
     protocol: auto # Optional. Specifies protocol to use, either amqp or http, or auto to autodetect based on the `host` value. Default value is auto.
-    queueLength: '20' # Optional. Queue length target for HPA. Default: 20 messages
+    queueLength: '20' # Optional. Queue length target for HPA. Default: 20 messages if `publishRate` is not specified, or 0 if `publishRate` is specified
+    publishRate: '100' # Optional. Publish/sec. target on the queue for HPA. Requires http host/protocol
     queueName: testqueue
     vhostName: / # Optional. If not specified, use the vhost in the `host` connection string.
     # Alternatively, you can use existing environment variables to read configuration from:
@@ -31,7 +32,8 @@ triggers:
     `http://guest:password@localhost:15672/vhost`. When using a username/password consider using `hostFromEnv` or a TriggerAuthentication.
 
 - `queueName`: Name of the queue to read message from. Required.
-- `queueLength`: Target value for queue length passed to the scaler. Example: if one pod can handle 10 messages, set the queue length target to 10. If the actual number of messages in the queue is 30, the scaler scales to 3 pods. Default is 20. Optional.
+- `queueLength`: Target value for queue length passed to the scaler. Example: if one pod can handle 10 messages, set the queue length target to 10. If the actual number of messages in the queue is 30, the scaler scales to 3 pods. Default is 20 unless `publishRate` is specified, in which case `queueLength` is disabled for this trigger. Optional and exclusive with `publishRate`.
+- `publishRate`: Target value for queue publish/sec. rate passed to the scaler. Example: if one pod can handle 100 messages/sec., set the publishRate target to 100. If the actual publish/sec. rate on the queue is 500/sec., the scaler scales to 5 pods. `http` protocol is requried to use `publishRate`. Optional and exclusive with `queueLength`
 - `protocol`: Protocol to be used for communication. Either `auto`, `http`, or `amqp`. It should correspond with the `host` value. Optional, will autodetect based on the `host` URL if possible.
 - `vhostName`: Vhost to use for the connection, overrides any vhost set in the connection string from `host`/`hostFromEnv`.
 
@@ -44,6 +46,8 @@ Some parameters could be provided using environmental variables, instead of sett
 
 > ⚠ **Important:** if you have unacknowledged messages and want to have these counted for the scaling to happen, make sure to utilize the `http` REST API interface which allows for these to be counted.
 
+> ⚠ **Important:** a trigger can only have one of `queueLength` or `publishRate` specified (or neither specified which will set `queueLength` to the default value). If scaling against both is desired then the `ScaledObject` should have two triggers, one for `queueLength` and the other for `publishRate`. HPA will scale based on the largest result considering each of the two triggers independently.
+
 ### Authentication Parameters
 
 TriggerAuthentication CRD is used to connect and authenticate to RabbitMQ:
@@ -94,7 +98,7 @@ spec:
       name: keda-trigger-auth-rabbitmq-conn
 ```
 
-#### HTTP protocol:
+#### HTTP protocol (`queueLength`):
 
 ```yaml
 apiVersion: v1
@@ -132,3 +136,49 @@ spec:
     authenticationRef:
       name: keda-trigger-auth-rabbitmq-conn
 ```
+
+#### HTTP protocol (`publishRate` and `queueLength`):
+
+```yaml
+apiVersion: v1
+kind: Secret
+metadata:
+  name: keda-rabbitmq-secret
+data:
+  host: <HTTP API endpoint> # base64 encoded value of format http://guest:password@localhost:15672/vhost
+---
+apiVersion: keda.sh/v1alpha1
+kind: TriggerAuthentication
+metadata:
+  name: keda-trigger-auth-rabbitmq-conn
+  namespace: default
+spec:
+  secretTargetRef:
+    - parameter: host
+      name: keda-rabbitmq-secret
+      key: host
+---
+apiVersion: keda.sh/v1alpha1
+kind: ScaledObject
+metadata:
+  name: rabbitmq-scaledobject
+  namespace: default
+spec:
+  scaleTargetRef:
+    name: rabbitmq-deployment
+  triggers:
+  - type: rabbitmq
+    metadata:
+      protocol: http
+      queueName: testqueue
+      queueLength: "20"
+    authenticationRef:
+      name: keda-trigger-auth-rabbitmq-conn
+  - type: rabbitmq
+    metadata:
+      protocol: http
+      queueName: testqueue
+      publishRate: "100"
+    authenticationRef:
+      name: keda-trigger-auth-rabbitmq-conn
+```