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In this guide, you’ll learn how to automatically scale a Kubernetes worker service by monitoring a Redis list backlog with KEDA. This approach is perfect for scenarios like an online store during a flash sale, where incoming orders outpace your processing capacity.
The image illustrates an e-commerce scenario during a big sale or holiday season, showing a laptop with multiple shopping cart icons and a connection to a worker service.

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Why Redis List Scaling?

Traditional CPU- or memory-based scaling won’t address a growing Redis queue. By using KEDA’s Redis List scaler, you can dynamically adjust pod replicas based on the number of pending items:
  • Scale out when the backlog grows.
  • Scale in when work completes.
  • Avoid overprovisioning during low traffic.

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Architecture and Flow

Below is a high-level diagram showing how Redis, KEDA, and your worker deployment interact:
The image is a diagram showing a flow from Redis to KEDA, with two intermediary icons representing data and users.
KEDA monitors the length of the Redis list and drives the Horizontal Pod Autoscaler (HPA) for your target deployment.
The image illustrates "KEDA Scaling With 'redis' List" and features three components: Secret, TriggerAuthentication, and ScaledObject, each represented by an icon.

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KEDA Resources Overview

ResourcePurposeDocumentation
SecretStores the Redis password (Base64-encoded)Kubernetes Secrets
TriggerAuthenticationReferences the secret to authenticate KEDA to RedisKEDA Auth Concepts
ScaledObjectDefines how to scale your worker based on the listKEDA ScaledObject

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1. Create the Redis Password Secret

Encode your Redis password in Base64 and store it in a Kubernetes Secret: 
apiVersion: v1
kind: Secret
metadata:
  name: auth-redis-secret
type: Opaque
data:
  redis_password: amhibm9pdWhramo=
Ensure you encode the plaintext password with base64.
For example: echo -n 'yourRedisPassword' | base64

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2. Define TriggerAuthentication

Create a TriggerAuthentication so that KEDA can retrieve the password from the secret: 
apiVersion: keda.sh/v1alpha1
kind: TriggerAuthentication
metadata:
  name: keda-trigger-auth-redis-secret
spec:
  secretTargetRef:
    - parameter: password
      name: auth-redis-secret
      key: redis_password

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3. Configure the ScaledObject

Finally, define the ScaledObject to tie everything together: 
apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: redis-scaledobject
spec:
  scaleTargetRef:
    name: nginx
  minReplicaCount: 1
  triggers:
    - type: redis
      metadata:
        address: redis.default.svc.cluster.local:6379
        listName: myList
        listLength: "10"
      authenticationRef:
        name: keda-trigger-auth-redis-secret
  advanced:
    horizontalPodAutoscalerConfig:
      behavior:
        scaleDown:
          stabilizationWindowSeconds: 20
          policies:
            - type: Percent
              value: 50
              periodSeconds: 20
        scaleUp:
          stabilizationWindowSeconds: 0
          policies:
            - type: Percent
              value: 100
              periodSeconds: 15
Review your HPA policies carefully. Aggressive scaling (100% every 15 s) can lead to resource spikes. Adjust thresholds to match your cluster capacity.
With this setup, KEDA will watch the myList backlog in Redis and automatically scale the nginx worker pods—scaling out under heavy load and scaling in as the queue drains.

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References

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