Why

This service has been designed to be compatible with future autoscale-to-zero logic in kubernetes itself. Until then - you have either use something like KEDA, or implement it by yourself

Known Limitations

• Only Object and External metrics are supported
• Only Deployment is supported as HPA target
• Metric selector MatchExpressions is not supported

Architecture overview

sequenceDiagram
loop every minute
    HpaInformer->>+autoscaling.k8s.io: subscribe
    autoscaling.k8s.io-->>-HpaInformer: Updates
    par for every hpa
        HpaInformer->>Goroutines: new
        loop every minute
            par for every metric
                Goroutines->>+*.metrics.k8s.io: Give me actual state
                *.metrics.k8s.io-->>-Goroutines: result
            end   
            alt All metrics are 0 AND Replicas > 0
                Goroutines->>+autoscaling.k8s.io: scale to 0
                autoscaling.k8s.io-->>-Goroutines: ok
            else Any metric is not 0 AND Replicas == 0
                Goroutines->>+autoscaling.k8s.io: scale to 1
                autoscaling.k8s.io-->>-Goroutines: ok
            end
            autoscaling.k8s.io-->>HpaInformer: Hpa exists no more
            HpaInformer->>Goroutines: die
        end
    end
end

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Available metrics

scale_to_zero_errors
scale_to_zero_events
scale_to_zero_panics

Howto test locally

You can install demo services from the ./demo folder

kubectl apply -f app.yml -n integration-demo
kubectl apply -f metric-generator.yml -n integration-demo

to have multiple deployments with multiple random metrics bouncing between 0 and 1

Now you can run service locally to scale services in a real kube cluster: go run ./cmd --kube-config "<path to your kube config>" --write-plain-logs --hpa-selector "scaleToZero.spscommerce.com/watch=true"