Modern Scalable Architecture

How I Understand a Scalable Application Architecture  

Article By: Radhakrishnan A Perumal

(From My DevOps Learning Journey)

While learning DevOps, AWS, Docker, and Kubernetes,  

I wanted to understand how a scalable application actually works  

from start → end.

This is the architecture that finally made sense to me 👇


🌍 1. DNS & Global Routing


When a user hits our domain:

 1️⃣ DNS (Route53 / Cloudflare) finds the nearest region  

 2️⃣ Routes the request there  

 3️⃣ Sends it to the Load Balancer  


👉 This reduces latency and improves response times globally.



⚖️ 2. Load Balancer


The Load Balancer:

 - Handles HTTPS  

 - Performs health checks  

 - Balances traffic across nodes  

 - Only forwards valid traffic  

 - Sends everything to Ingress  


🔒 Keeps the Kubernetes cluster safe behind it.



🔀 3. Ingress

Ingress is the **entry gate** into our Kubernetes cluster.


It handles:

 - Routing to the right service  

 - Path-based routing  

 - IP allow/block  

 - HTTPS termination inside the cluster  


Examples:

  /auth  → Auth Service  

  /orders → Order Service  

  /cart  → Cart Service  



🧩 4. Service (ClusterIP)

Ingress never talks directly to pods — it talks to Services.


Services provide:

  - A stable internal IP  

  - Load balancing between pods  

  - Internal DNS for microservices  



📦 5. Pods

Each microservice runs inside Pods.


Pods are:

 - Auto-scaled  

 - Restarted if they fail  

 - Spread across nodes  

 - Updated using rolling deployments  


💡 Kubernetes decides where Pods run.



🗄️ 6. Database Layer


Applications connect to managed DBs like RDS, Mongo Atlas, DynamoDB.


We get:

 - Backups  

 - Failover  

 - High availability  

 - Read replicas  


📌 This stabilizes the entire backend layer.



🔁 7. CI/CD Flow


My understanding of the deployment process:

 1. Developer pushes code  

 2. CI builds Docker image  

 3. Pushes image to ECR/Registry  

 4. CD applies Kubernetes YAML/Helm  

 5. API Server updates cluster state  

 6. Scheduler places pods  

 7. Load Balancer sends traffic to new pods  

✨ Result → Zero downtime deployments.

🗺️ 8. Simple Architecture Diagram

User  → DNS  → Load Balancer  → Ingress  → Service  → Pods  → Database

🌐 9. Multi-Region Setup (Advanced Learning)

To get global low latency:

 ✓ Multiple K8s clusters in different regions  

 ✓ Each region has its own DB replica  

 ✓ DNS routes user to nearest region  


🌎 This gives a truly global experience

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