🚀 How I Merged Multiple Kubernetes Clusters with Zero Downtime

Managing too many Kubernetes clusters? 😩 Been there. When your infra grows wild, merging clusters can reduce costs, simplify security, and cut DevOps headaches—but only if done right.

Here’s how I successfully consolidated multiple clusters into one without breaking production.

🔥 Why Merge Kubernetes Clusters?
Less Maintenance → No more juggling dozens of separate monitoring, logging, and security setups.

Lower Costs → One optimized cluster is cheaper than several underutilized ones.

Better Security → Centralized policies reduce the risk of misconfiguration.
🔹 1. Map Your Microservices
Before migration, know your dependencies. Example:
✅ star-app → Consumes API, sends messages to RabbitMQ
✅ comet-app → Listens to RabbitMQ, writes to Elasticsearch

🔑 Lesson: Move dependent services together or risk unexpected failures.

🔹 2. Unify Your Monitoring & Logging
I moved Prometheus, Grafana, and RabbitMQ into a single cluster:

additionalScrapeConfigs:
  - job_name: star-service
    static_configs:
      - targets: ['star-app.star-namespace:8080']

✅ Now, one dashboard tracks everything.

🔹 3. Fix Traffic Routing (Ingress / Istio)

🔴 Before: Each cluster had its own LoadBalancer (💸 $$$).
🟢 After: Unified traffic with two gateways:

External Gateway → For public requests
Internal Gateway → For microservices

kind: VirtualService
spec:
  hosts:
    - "star.mydomain.org"
  gateways:
    - external-gateway
  http:
    - match:
        - uri:
            prefix: /
      route:
        - destination:
            host: star-service
            port: 8080

✅ Fewer LoadBalancers, faster traffic routing.

🔹 4. Strengthen Security

🔒 Before: Cluster-wide open access 😱
🔐 After:
✔ Firewall rules to restrict external traffic
✔ JWT-based authentication for API access
✔ NetworkPolicies to control pod-to-pod communication

kind: NetworkPolicy
spec:
  ingress:
    - from:
        - namespaceSelector:
            matchLabels:
              istio-injection: enabled
      ports:
        - protocol: TCP
          port: 8080

✅ Locked down. No more unnecessary exposure.

🔹 5. Seamless Migration

✅ Deploy new cluster first → Debug everything in test
✅ Gradually switch traffic → Use DNS/load balancers to transition traffic
✅ Decommission old clusters → After validation
The result? 🚀
✅ 40% cost savings
✅ Unified monitoring & security
✅ No downtime

Want the full breakdown? 🔥
👉 Read the complete guide on Medium:
https://medium.datadriveninvestor.com/how-i-merged-multiple-kubernetes-clusters-with-zero-downtime-7c62f0a8c050
💬 Have you consolidated clusters before? What was your biggest challenge? Let’s discuss in the comments! 🚀