docs: Add Kubernetes Deployment Guide (#2654)

[unn-Known1]

Summary

Add comprehensive Kubernetes deployment documentation for DeerFlow, addressing issue #2654 which requests K8S deployment guidance.

Changes

• Added docs/KUBERNETES_DEPLOYMENT.md with complete Kubernetes deployment guide

Documentation Contents

The new Kubernetes Deployment Guide includes:

• Prerequisites: Cluster requirements and required tools
• Architecture Overview: Service topology diagram
• Configuration Preparation: Namespace, ConfigMap, and Secrets manifests
• Service Deployments: Complete YAML manifests for:
  • Gateway (FastAPI backend)
  • Frontend (Next.js)
  • Nginx reverse proxy
• Ingress Setup: External access configuration
• Scaling & HA: Horizontal Pod Autoscaler, Pod Disruption Budget, Resource Quotas
• Monitoring: Health checks and readiness probes
• Troubleshooting: Common issues and debugging commands
• Production Checklist: Pre-deployment verification items

Validation

• All YAML manifests validated for correct syntax (12/12 blocks pass validation)
• Follows existing documentation patterns in the repository
• Compatible with Kubernetes 1.25+

Testing Evidence

Found 12 YAML blocks
Block 1-12: Valid
All YAML blocks are valid!

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This contribution was developed with AI assistance.

[WillemJiang]

@unn-Known1 Thanks for your contribution. Did you have a chance to verify the entire K8S configuration in this document?

[unn-Known1]

Hi @WillemJiang, thank you for the review!

Regarding verification of the K8S configuration, here is what was validated:

Validation Performed:

1. YAML Syntax Validation: All 12 YAML blocks in the document were validated for correct syntax and passed validation.
2. K8s API Version Compatibility: All manifests use networking.k8s.io/v1 (available since K8s 1.19+), autoscaling/v2 (available since K8s 1.23+), and other stable APIs.
3. Architecture Consistency: The architecture diagram matches the actual service names and ports defined in the deployments.

What's NOT Live-Verified:
The document provides production-ready templates, but actual deployment testing requires:

• A running Kubernetes cluster (v1.25+)
• Docker images built and pushed to a registry
• Network configuration specific to your environment

The document includes:

• Namespace, ConfigMap, and Secrets manifests
• Gateway (FastAPI), Frontend (Next.js), and Nginx deployments
• PersistentVolumeClaim for data storage
• Ingress with TLS configuration
• HorizontalPodAutoscaler for scaling
• PodDisruptionBudget and ResourceQuota for HA
• Troubleshooting commands and production checklist

To verify on your cluster:

# Validate manifests with kubeval or kustomize
kubeval manifests/*.yaml

# Dry-run to check for errors
kubectl apply -f manifests/ --dry-run=server