How to fix unable to compute replica count in Kubernetes

Check if the Metrics Server deployment exists and is running:

kubectl get deployment metrics-server -n kube-system
kubectl get pods -n kube-system -l k8s-app=metrics-server
kubectl logs -n kube-system -l k8s-app=metrics-server | head -50

If metrics-server is missing, install it:

kubectl apply -f https://github.com/kubernetes-sigs/metrics-server/releases/latest/download/components.yaml

Test that the Metrics Server can gather and serve metrics:

kubectl top nodes
kubectl top pods -n <namespace>

If these commands return 'unknown' or 'Metrics not available yet', metrics collection is not working. Check Metrics Server logs for errors like 'TLS errors', 'connection refused', or 'unauthorized'.

The HPA cannot calculate utilization without knowing how much CPU/memory each pod requested. Update your Deployment with explicit requests:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  template:
    spec:
      containers:
      - name: app
        image: myimage:1.0
        resources:
          requests:
            cpu: 250m
            memory: 256Mi
          limits:
            cpu: 500m
            memory: 512Mi

Apply and rollout:

kubectl apply -f deployment.yaml
kubectl rollout status deployment/myapp -n <namespace>

If you use Istio, Linkerd, or other service meshes, proxies are automatically injected but often lack resource requests.

For Linkerd, add this annotation to your pod spec:

spec:
  template:
    metadata:
      annotations:
        config.linkerd.io/proxy-cpu-request: 100m
        config.linkerd.io/proxy-memory-request: 64Mi

For Istio, configure the sidecar injector to include resource requests:

kubectl get configmap istio-sidecar-injector -n istio-system -o yaml | grep -A 20 "resources:"

Recreate pods after updating to apply sidecar changes.

Examine the HPA object to understand what's failing:

kubectl get hpa -n <namespace>
kubectl describe hpa <hpa-name> -n <namespace>

Look for:
- Metrics: Verify it matches your container's resource requests
- Conditions: Look for 'ScalingActive = False' which indicates metrics cannot be fetched
- Events: Recent events will show exact errors like 'missing request for cpu'

The HPA cannot compute metrics if there are zero replicas running:

kubectl get pods -n <namespace> -l app=myapp
kubectl describe pod <pod-name> -n <namespace>

If minReplicas is 0 or pods are terminated, scale the deployment to at least 1:

kubectl scale deployment myapp --replicas=1 -n <namespace>

Wait for the pod to reach Ready state, then verify metrics appear:

kubectl top pods -n <namespace>

Note: Standard HPA cannot scale down to zero. For scale-to-zero, consider KEDA.