Centralized API Gateway or Cloud API Gateway??

🧭 Context

• You have a multi-cloud hybrid setup:

  • Region A (Azure) → Hosts digital lending & onboarding

  • Region B (AWS) → Hosts fraud analytics & AI models

  • Region C (On-Prem DC) → Hosts CBS & PII-sensitive data

You now need a common API exposure strategy across all three — to securely expose and consume APIs between services, partners, and external channels.

⚙️ Step 1: Decide the API Management Pattern

You have two main architecture choices here:

Pattern	Description	When to Use
Pattern 1: Federated API Gateways (Per Cloud)	Each environment uses its own native API gateway — e.g., Azure API Management (APIM), AWS API Gateway, Apigee (GCP). They synchronize metadata or routing through a central control plane.	✅ Best for regulatory and latency-sensitive BFSI environments.
Pattern 2: Centralized Global API Gateway (Cloud-neutral)	One enterprise-level API gateway (e.g., Kong, Apigee, or Tyk) deployed centrally — acts as global entry point for all traffic, routing to backends in different clouds.	✅ Best for global multi-cloud where single entry and uniform policy control needed.

🧩 Step 2: BFSI Recommended Approach (Federated + Central Control)

In regulated BFSI (like ABC Bank, HDFC, or ICICI), the federated model with central governance is preferred.Here’s why 👇

✅ Advantages:

• Each region can operate independently (DR or isolation friendly).

• Data residency — Indian PII data never leaves Azure India region.

• Cloud-native integration — each gateway integrates natively with respective cloud IAM, logging, WAF, etc.

• You maintain central policy synchronization using API catalog & governance.

🧱 Step 3: Architecture Flow (Text Version)

Example: Loan Origination API (Azure) → Fraud Scoring (AWS) → Account Creation (On-Prem CBS)

1. Client / Mobile App callshttps://api.bank.com/lending/loan/initiate(entry via central API gateway DNS, e.g., api.bank.com).

2. Global DNS (Traffic Manager / Cloudflare) routes call to nearest cloud (Azure in India region).

3. Azure API Management (APIM) receives the request

   • Authenticates via Azure AD

   • Applies rate limiting, JWT validation, logging

   • Routes call to Azure Loan microservice

4. Loan service calls Fraud Scoring API hosted on AWS →Calls are proxied via Azure APIM → AWS API Gateway (via private interconnect / VPC Peering)

5. Fraud Score returned → Loan Approved Event → Published to Kafka (Azure)

6. Kafka MirrorMaker replicates event to on-prem Kafka →CBS adapter consumes it → Creates account → Sends acknowledgment.

7. Each gateway (Azure APIM, AWS API GW, On-Prem API GW like Kong)syncs API specs with central API Catalog (ServiceNow / SwaggerHub) for governance and discovery.

🛡️ Step 4: Security & Governance

Layer	Control
Authentication	Central IAM (Azure AD / PingFed) integrated with each gateway
Authorization	Token-based + fine-grained scopes (OpenID / OAuth2)
Transport Security	Mutual TLS across gateways
Governance	Central API registry with version control & approval workflow
Observability	Common tracing via OpenTelemetry or API Observability platform (Datadog / Dynatrace)

🧩 Step 5: Alternate — Cloud-Agnostic Gateway (Centralized)

If the bank wants a single unified control plane, you can use:

• Kong Enterprise, Apigee X, or Tyk Cloud-Native Gateway

• Deployed across all clouds in cluster mode

• Federated agents installed on Azure, AWS, and on-prem

Architecture Flow

1. Single API Gateway cluster spans clouds.

2. Agents in each cloud route requests locally (for latency).

3. Policies, throttling, and keys managed centrally.

4. Common developer portal for internal & partner developers.

🧠 Step 6: Summary

“In a multi-cloud BFSI setup , I recommend a federated API gateway architecture — where each region (Azure, AWS, and on-prem) hosts its own API gateway component (Azure APIM, AWS API Gateway, and Kong on-prem). This ensures compliance with data residency, low latency, and independent failover, while maintaining centralized governance and discoverability through a global API catalog and policy repository. Secure private interconnects (ExpressRoute, Direct Connect, VPN) link the environments, allowing cross-cloud API calls using mTLS and token-based authentication. Alternatively, if the enterprise prefers uniform policy enforcement across all clouds, we can deploy a cloud-agnostic API gateway (e.g., Kong or Apigee) with federated data planes across clouds and a unified control plane.”

✅ Key takeaway for interviews:

• There’s no single API gateway across clouds unless you deploy a cloud-agnostic one (e.g., Kong, Apigee, Tyk).

• In BFSI, most prefer “federated API gateways per region + central governance” for compliance and resiliency.

Excellent follow-up 👏 — and yes, you’re absolutely right to think in terms of “common URL” because that’s where most architects get confused during multi-cloud design.

Let’s go step by step — this is a subtle but very important concept for your Enterprise Architect interview.

🧭 Context

You have a multi-cloud hybrid deployment:

Region	Platform	Hosted Workloads
Azure (India)	Digital Lending APIs	Loan origination, onboarding
AWS (Singapore)	Fraud & Analytics APIs	Fraud scoring, AI models
On-Prem (India DC)	CBS & Regulatory Systems	Account management, reporting

You now want to expose a single consistent API endpoint to internal/external consumers (e.g., mobile app, partner APIs).

⚙️ Step 1: Understand What “Centralized API Gateway” Really Means

A centralized API gateway does not mean a single physical instance or one URL sitting in one cloud.It means a logically unified control plane (policies, API catalog, tokens, developer portal, rate limits) and distributed data planes in each region/cloud.

So yes — consumers see one common entry point (URL),but traffic is actually routed to the nearest or most appropriate region behind the scenes.

🌐 Step 2: Common URL Strategy (DNS Layer)

Yes, you can have a common URL for all multi-cloud regions, e.g.:

https://api.bank.com

This URL is managed by Global DNS — examples:

• Azure Traffic Manager

• AWS Route 53

• Cloudflare

• Akamai GTM

How It Works

1. Client calls https://api.bank.com/loan/initiate.

2. DNS routes based on:

   • Geo-proximity (nearest region)

   • Health check / availability

   • Business routing logic (e.g., India → Azure, EU → AWS)

3. Once request lands in chosen region:

   • It is handled by the local API gateway (Azure APIM or AWS API Gateway).

   • Policies, authentication, rate limits, etc. are applied.

4. Gateway routes internally to respective microservice (cloud-native or on-prem via private link).

✅ Result

• Single public URL

• Multi-region, multi-cloud backend

• Central governance and consistent experience

🧩 Step 3: Implementation Variants

Option 1 – DNS-Based Routing (Most Common)

api.bank.com → DNS routes → region-specific API gateways

• Cloud-agnostic

• Low complexity

• Recommended for BFSI with strict data sovereignty

Option 2 – Global API Gateway (Cloud-Agnostic Tool)

e.g. Kong Enterprise, Apigee X, Tyk Hybrid

• Single control plane manages global policies, users, and rate limits.

• Each cloud has local data plane (API gateway instance).

• Common developer portal & catalog.

• DNS/Load balancer routes to nearest data plane.

Option 3 – Cloud Load Balancer Fronting Regional Gateways

• Cloudflare, F5, or Avi Networks frontends route to multiple cloud gateways.

• Common URL terminates at global LB → forwards to respective gateway via private interconnect.

🛡️ Step 4: Security & Compliance

Control	Implementation
Authentication	OAuth2.0 / OIDC via centralized IAM (Azure AD / PingFed / ForgeRock)
Encryption	mTLS end-to-end between consumer ↔ gateway ↔ backend
Data Residency	DNS routes India traffic only to Azure India (PII compliant)
DR	Secondary region routing via health probe failover
Audit	Central API analytics + per-region log retention

🧠 Step 5: Answer (Text Version)

“In a multi-cloud environment, yes — we can absolutely have a common URL for all APIs (like https://api.bank.com), even though services are deployed across Azure, AWS, and on-prem. We achieve this through global DNS routing or a centralized API gateway control plane. The DNS resolves the common URL to the nearest or compliant regional gateway — for instance, Azure APIM for India workloads and AWS API Gateway for global fraud analytics. Each gateway enforces consistent policies, authentication, and logging as defined centrally. So, while the endpoint appears unified to consumers, the traffic is regionally terminated, ensuring low latency, compliance, and resilience. This pattern is widely used in BFSI where you want global consistency with local control.”

✅ Key Takeaways:

Question	Answer
Can we have one URL for multi-cloud APIs?	✅ Yes — via global DNS / centralized control plane
Is the API Gateway physically common?	❌ No — logically unified, physically distributed
Why is this better?	Data residency, low latency, independent failover, consistent security
Tools to achieve this	Cloudflare, Azure Traffic Manager, Apigee X, Kong Enterprise