RabbitMQ scaler does not support custom metricName

[rtnpro]

Report

In our use case, workers consume from multiple RabbitMQ hosts on the same queue name, and failover if a host goes out of service. However, without support for custom metricName in TriggerMetadata like other scalers like postgresql, triggers on the same queue, mode but different RabbitMQ hosts create duplicate metricName in Keda, and hence there's an error during reconciling the ScaledObject.

# Add auth for host-1
apiVersion: keda.sh/v1alpha1
kind: TriggerAuthentication
metadata:
  name: worker-rabbitmq-trigger-auth-host-1
spec:
  secretTargetRef:
    - parameter: host
      name: keda-worker-secrets
      key: RABBITMQ_HOST_1
---
apiVersion: keda.sh/v1alpha1
kind: TriggerAuthentication
metadata:
  name: worker-rabbitmq-trigger-auth-host-2
spec:
  secretTargetRef:
    - parameter: host
      name: keda-worker-secrets
      key: RABBITMQ_HOST_2

---
apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: worker-scaleobject
spec:
  scaleTargetRef:
    name: some-worker
  triggers:
  - type: rabbitmq
    metadata:
      protocol: http
      queueName: somequeue
      mode: QueueLength
      value: "100"
    authenticationRef:
      name: rabbitmq-trigger-auth-host-1
  - type: rabbitmq
    metadata:
      protocol: http
      queueName: somequeue
      mode: QueueLength
      value: "100"
    authenticationRef:
      name: rabbitmq-trigger-auth-host-2

Expected Behavior

RabbitMQ Scaler should allow & parse custom metricName in TriggerMetadata, so that in the above reported use case, we can prevent duplicate metricNames in a ScaledObject by specifying custom metricName.

Actual Behavior

RabbitMQ scaler does not allow and parse metricName from TriggerMetadata.

Steps to Reproduce the Problem

1. Create a ScaledObject for a Deployment with multiple triggers using the same mode, queue, but on different hosts, similar to the snippet shared in the report above.

Logs from KEDA operator

2021-07-21T07:54:50.558Z	ERROR	controller	Reconciler error	{"reconcilerGroup": "keda.sh", "reconcilerKind": "ScaledObject", "controller": "scaledobject", "name": "worker-scaleobject", "namespace": "********", "error": "metricName rabbitmq-somequeue defined multiple times in ScaledObject worker-scaleobject, please refer the documentation how to define metricName manually"}
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem
	/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.6.5/pkg/internal/controller/controller.go:218
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).worker
	/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.6.5/pkg/internal/controller/controller.go:197
k8s.io/apimachinery/pkg/util/wait.BackoffUntil.func1
	/go/pkg/mod/k8s.io/apimachinery@v0.20.7/pkg/util/wait/wait.go:155
k8s.io/apimachinery/pkg/util/wait.BackoffUntil
	/go/pkg/mod/k8s.io/apimachinery@v0.20.7/pkg/util/wait/wait.go:156
k8s.io/apimachinery/pkg/util/wait.JitterUntil
	/go/pkg/mod/k8s.io/apimachinery@v0.20.7/pkg/util/wait/wait.go:133
k8s.io/apimachinery/pkg/util/wait.Until
	/go/pkg/mod/k8s.io/apimachinery@v0.20.7/pkg/util/wait/wait.go:90

KEDA Version

2.3.0

Kubernetes Version

1.17

Platform

Amazon Web Services

Scaler Details

RabbitMQ

Anything else?

No response

[tomkerkhove]

Thanks for your contribution on this @rtnpro!