document new publishRate trigger (#388)

Co-authored-by: Karg <rkarg@blizzard.com>

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
+    mode: QueueLength # QueueLength or MessageRate
+    value: 100 # message backlog or publish/sec. target per instance
     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:
@@ -27,23 +28,28 @@ triggers:
 
 **Parameter list:**
 
-- `host`: Host of RabbitMQ with format `amqp://<host>:<port>/vhost`. The resolved host should follow a format like `amqp://guest:password@localhost:5672/vhost` or
+- `host`: Host of RabbitMQ with format `<protocol>://<host>:<port>/vhost`. The resolved host should follow a format like `amqp://guest:password@localhost:5672/vhost` or
     `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.
+- `mode`: QueueLength to trigger on number of messages in the queue. MessageRate to trigger on the publish rate into the queue. Required.
+- `value`: Message backlog or Publish/sec. rate to trigger on
 - `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`.
-
+- `queueLength`: DEPRECATED! Use `mode: QueueLength` and `value: ##` instead. 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.
 
 Some parameters could be provided using environmental variables, instead of setting them directly in metadata. Here is a list of parameters you can use to retrieve values from environment variables:
 
 - `hostFromEnv`: The host and port of the Redis server, similar to `host`, but reads it from an environment variable on the scale target.
 
 > 💡 **Note:** `host`/`hostFromEnv` has an optional vhost name after the host slash which will be used to scope API request.
 
+> 💡 **Note:** `mode: MessageRate` requires protocol `http`.
+
 > ⚠ **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:** If scaling against both is desired then the `ScaledObject` should have two triggers, one for `mode: QueueLength` and the other for `mode: MessageRate`. 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:
@@ -89,12 +95,53 @@ spec:
     metadata:
       protocol: amqp
       queueName: testqueue
-      queueLength: "20"
+      mode: QueueLength
+      value: "20"
+    authenticationRef:
+      name: keda-trigger-auth-rabbitmq-conn
+```
+
+#### HTTP protocol (`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
+      mode: QueueLength
+      value: "20"
     authenticationRef:
       name: keda-trigger-auth-rabbitmq-conn
 ```
 
-#### HTTP protocol:
+#### HTTP protocol (`MessageRate` and `QueueLength`):
 
 ```yaml
 apiVersion: v1
@@ -128,7 +175,16 @@ spec:
     metadata:
       protocol: http
       queueName: testqueue
-      queueLength: "20"
+      mode: QueueLength
+      value: "20"
+    authenticationRef:
+      name: keda-trigger-auth-rabbitmq-conn
+  - type: rabbitmq
+    metadata:
+      protocol: http
+      queueName: testqueue
+      mode: MessageRate
+      value: "100"
     authenticationRef:
       name: keda-trigger-auth-rabbitmq-conn
 ```