gke-workload-scaling

GKE Workload Scaling

This skill provides workflows and best practices for scaling applications on

Google Kubernetes Engine (GKE). It covers manual scaling, Horizontal Pod

Autoscaling (HPA), and Vertical Pod Autoscaling (VPA).

Workflows

1. Manual Scaling

Scale a deployment to a fixed number of replicas. Useful for immediate manual

intervention or testing.

Command:

kubectl scale deployment {deployment_name} --replicas={number} -n {namespace}

# Verify the scale event
kubectl get deployment {deployment_name} -n {namespace}

2. Horizontal Pod Autoscaling (HPA)

Automatically scale the number of pods based on observed CPU utilization, memory

utilization, or custom metrics.

Prerequisites:

• Metrics Server must be running (enabled by default on GKE).
• Containers clearly define resource requests/limits.

Quick Command:

kubectl autoscale deployment {deployment_name} --cpu-percent=50 --min=1 --max=10

Manifest Approach (Recommended): Use a YAML manifest for version-controlled

configuration. See [assets/hpa-example.yaml](assets/hpa-example.yaml) for a

template.

kubectl apply -f assets/hpa-example.yaml

# Verify HPA is created and fetching metrics
kubectl get hpa

Custom Metrics & External Metrics: For GKE, the modern and recommended

approach for scaling based on Cloud Monitoring metrics (e.g., Pub/Sub queue

length) is to use the External metric type, which is natively supported by

the GKE control plane without requiring the Custom Metrics Adapter. For

application-specific metrics exposed via Prometheus, you can use **Google Cloud

Managed Service for Prometheus** or the Prometheus Adapter.

3. Vertical Pod Autoscaling (VPA)

Automatically adjust the CPU and memory reservations for your pods to match

actual usage. This is critical for right-sizing workloads.

Prerequisites:

• VPA must be enabled on the cluster.
• Autopilot: Enabled by default.
• Standard: Must be enabled manually.

Enable VPA on Standard Cluster:

gcloud container clusters update {cluster_name} --enable-vertical-pod-autoscaling --zone {zone}

Update Modes:

• Off: Calculates recommendations but does not apply them. Good for "dry

run" analysis.

• Initial: Assigns resources only at pod creation time.
• Auto: Updates running pods by restarting them if recommendations differ

significantly from requests.

• InPlaceOrRecreate: Attempts to update Pod resources without recreating the

Pod. If in-place update is not possible, it reverts to Auto mode (requires

GKE 1.34+).

Example: See [assets/vpa-example.yaml](assets/vpa-example.yaml) for a

configuration template.

Best Practices

1. Define Resource Requests: HPA and VPA rely on accurate resource

requests. Always define them in your container specs.

1. Avoid Metric Conflicts: Do not configure HPA and VPA to use the same

metric (e.g., both CPU). This causes thrashing.

• Typical Pattern: HPA on CPU, VPA on Memory.

1. Pod Disruption Budgets (PDBs): Define PDBs to ensure application

availability during scaling events or node upgrades.

1. HPA Lag: HPA has a stabilization window (default 5 mins) to prevent

rapid fluctuation.

1. VPA "Auto" Mode Risks: In "Auto" mode, VPA restarts pods to change

resources. Ensure your application handles restarts gracefully (e.g.,

handles SIGTERM).

• Note: By default, VPA requires at least 2 replicas to perform

evictions (to prevent a situation where the only running replica is

evicted, causing downtime). In GKE 1.22+, you can override this by

setting minReplicas in PodUpdatePolicy.

Rightsizing Workflow

1. Deploy VPA in Off mode for 24+ hours
2. Read recommendations: `kubectl describe vpa {deployment_name}-vpa -n

{namespace}`

1. Compare target values against current requests
2. Apply with 20% buffer: new_request = target * 1.2
3. Use patch format or update deployment manifest to apply new resource

requests

Condition | Recommendation | Risk

----------------------------- | ------------------------------------ | ------

CPU request >5x P95 actual | Reduce to P95 * 1.2 | Medium

Memory request >3x P95 actual | Reduce to P95 * 1.2 | Medium

CPU request >2x P95 actual | Rightsizing with 20% buffer | Low

No resource limits set | Add limits to prevent noisy-neighbor | Low