Federated /Global API Gateway in Multi Cloud

🧭 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 Deut Bank, HDFCC, or ICICCI), 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 calls https://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:

“In a multi-cloud BFSI setup like ABC Bank, 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

• 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: Summary

“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

🔹 api.bank.com (common URL)

🔹 DNS routing to Azure / AWS / On-Prem

🔹 Local gateways applying policies

🔹 Backends communicating over hybrid links

🎯 Question:

In a multi-cloud + on-prem hybrid setup (e.g., Azure + AWS + On-Prem), can we have a centralized API Gateway with a single common URL for all environments?

✅ Step-by-Step Explanation and Realistic Enterprise Approach (e.g., Deutsche Bank Scenario)

Step 1️⃣ — Understand the Enterprise Setup

Let’s assume:

• Azure Region A → hosts Digital Lending platform

• AWS Region B → hosts Customer Engagement and CRM microservices

• On-Prem (Private DC) → hosts Core Banking System (CBS) and Regulatory Data Hub

So, there are 3 environments:

1. Azure Cloud

2. AWS Cloud

3. On-Prem Data Center

Now, each environment could have its own API Gateway for internal microservice routing.But the enterprise wants a common public endpoint — for example:

https://api.deutschebank.com/

instead of separate ones like:

https://azure-api.deutschebank.com/
https://aws-api.deutschebank.com/

Step 2️⃣ — Identify the Design Options

Option A — Distributed Gateways (Per Cloud)

Each cloud uses its native gateway:

• Azure → Azure API Management (APIM)

• AWS → AWS API Gateway

• On-Prem → Kong / Apigee / NGINX

Then, these gateways are fronted by a Global DNS + Reverse Proxy layer to route based on subdomain or path:

https://api.deutschebank.com/lending → Azure APIM
https://api.deutschebank.com/crm → AWS API Gateway
https://api.deutschebank.com/core → On-Prem API Gateway

✅ Pros:

• Native integration with each cloud platform

• High performance within each cloud region

❌ Cons:

• Complex routing configuration

• Multiple gateway management overhead

Option B — Centralized Global Gateway

Use one single enterprise API gateway as the entry point (e.g., Apigee, Kong, Mulesoft, or Azure Front Door + Global Traffic Manager).It then routes requests internally to each environment’s services.

For example:

• Global Gateway (Apigee X) deployed in multi-region mode

• Routes traffic securely via VPN / ExpressRoute / Private Link to:

  • Azure microservices (via internal APIM)

  • AWS microservices (via AWS PrivateLink)

  • On-Prem CBS (via MPLS / ExpressRoute / VPN)

✅ Pros:

• Unified URL and developer experience

• Single point for policies (AuthN/Z, throttling, logging, transformation)

• Easier to enforce standards, compliance, and security

❌ Cons:

• Slight latency due to routing through global gateway

• Requires redundant setup for HA (active-active gateways)

Step 3️⃣ — Connectivity Setup

To ensure hybrid connectivity:

• Azure ↔ On-Prem: via ExpressRoute

• AWS ↔ On-Prem: via Direct Connect

• Azure ↔ AWS: via Private interconnect or VPNAll connected through Transit Gateway or SD-WAN overlay network.

So your Global Gateway can reach internal services securely via private IPs — no public exposure.

Step 4️⃣ — Routing Mechanism (How Centralized API Works)

Let’s say the user calls:

POST https://api.deutschebank.com/lending/loan/apply

1. Request hits Global API Gateway (Apigee X or Azure Front Door)

2. Gateway performs:

   • Authentication (OAuth2/JWT)

   • Request validation

   • Policy enforcement

3. Based on route mapping, gateway forwards:

   • /lending/* → Azure APIM (via ExpressRoute)

   • /crm/* → AWS API Gateway (via PrivateLink)

   • /core/* → On-Prem NGINX gateway (via MPLS)

4. Response flows back through the same secure channel.

Step 5️⃣ — Deployment & Governance

• Use Terraform or Pulumi to automate multi-cloud gateway deployments

• Maintain a centralized API catalog (e.g., Azure API Center or SwaggerHub)

• Enable observability (logs, metrics, tracing) via a central system like Datadog / Splunk / Dynatrace

Step 6️⃣ — Why Common URL Matters

• Consistent branding (api.deutschebank.com)

• Simplifies integration for fintech partners and mobile apps

• Enables centralized API key / token management

• Avoids hardcoding per-cloud endpoints

Step 7️⃣ — Summary

Layer	Component	Cloud/Location	Purpose
Entry	Global API Gateway (Apigee / Mulesoft / Front Door)	Multi-Region	Single public endpoint
Routing	Azure APIM	Azure	Routes to lending APIs
Routing	AWS API Gateway	AWS	Routes to CRM APIs
Routing	NGINX / Kong	On-Prem	Routes to CBS APIs
Connectivity	ExpressRoute + DirectConnect + VPN	Hybrid	Secure interconnect
Observability	Central APM + Logging	Multi-Cloud	End-to-end monitoring

Summary

How will you design a centralized API gateway for multi-cloud and hybrid banking architecture?

Answer: In a regulated banking setup like Deutsche Bank, we use a centralized enterprise API gateway (e.g., Apigee X) that exposes a single unified URL for all public APIs. The gateway enforces global policies and routes requests internally to regional gateways — Azure APIM, AWS API Gateway, or On-Prem Kong — via secure private links (ExpressRoute, Direct Connect, MPLS). This allows us to maintain hybrid connectivity, ensure zero-trust security, and present a unified API experience to fintech partners and digital channels, while keeping sensitive systems like CBS within the on-prem boundary.

Excellent — this is the real-world, production-level explanation 👇Let’s look at exactly how large banks like Deutsche Bank, HSBC, Citi, or HDFC implement this multi-cloud + on-prem hybrid API gateway model in production.

🏦 Real Enterprise Scenario — Production Hybrid Setup

1️⃣ Typical Landscape

Environment	Platform	Example Workload
Azure Cloud (Mumbai Region)	Azure Kubernetes Service (AKS), Azure SQL, Azure APIM	Digital Lending, Customer Onboarding
AWS Cloud (Mumbai Region)	EKS, RDS, AWS API Gateway	CRM, Digital Marketing, Notifications
On-Prem Data Center (Pune or Navi Mumbai)	IBM / VMware clusters, Oracle DB, Finacle CBS, Payment Switch	Core Banking, Payments, Regulatory Systems

2️⃣ Why Hybrid Is Needed

Even though lending, onboarding, and CRM are cloud-native:

• Regulatory or sensitive systems (CBS, AML, Payment Hub) cannot move to public cloud.

• They are retained on-prem due to RBI, GDPR, and internal data sovereignty policies.

• Still, these systems must interact with cloud-native systems (like lending).

👉 So hybrid connectivity becomes mandatory — not optional.

3️⃣ Network & Connectivity Setup (Production Reality)

a. Private Network Links

Each environment is privately connected — no traffic goes over the public internet.

Connection Type	From	To	Description
Azure ExpressRoute	Azure VNet	On-Prem	Private 10 Gbps MPLS link for CBS and regulatory data exchange
AWS Direct Connect	AWS VPC	On-Prem	Secure pipe for CRM and notification systems
Azure ↔ AWS Peering	Azure VNet	AWS VPC	Private VPN or Megaport / Equinix interconnect for cross-cloud service calls

💡 These links terminate in a central DMZ zone within the bank’s enterprise network where firewalls, load balancers, and proxies enforce all traffic rules.

b. DNS & Routing

• DNS zones like api.deutschebank.com are managed centrally (often via Akamai, Infoblox, or Azure DNS).

• Routing policies (geo + latency-based) ensure:

  • Requests from India hit Azure Mumbai first

  • Failover to AWS Mumbai if needed (active-active setup)

4️⃣ API Gateway Design in Production

Layered Architecture

Layer	Product Used	Purpose
Global Gateway (Entry Point)	Apigee X / Mulesoft / Kong Enterprise	Common external endpoint (api.deutschebank.com)
Regional Gateways	Azure APIM / AWS API Gateway / NGINX (On-Prem)	Environment-specific service routing
Internal Mesh	Istio / Dapr / Consul	Service-to-service discovery within each region

How Traffic Flows in Real Life

Example → Customer applies for a loan via mobile app.

1. https://api.deutschebank.com/lending/apply→ Hits Apigee Global Gateway hosted in HA across Azure & AWS.

2. Apigee authenticates (OAuth2 token validation with Azure AD / PingFed).

3. Apigee routes the call to the right backend:

   • Lending microservice on Azure AKS

   • via private ExpressRoute peered network

4. Lending service needs to check CBS account eligibility.

   • Publishes message to Kafka topic hosted on Azure (private endpoint)

   • On-Prem CBS adapter consumes from same topic via ExpressRoute link

   • Adapter writes back loan_account_created event

5. Response sent back to Apigee → client.

   • End-to-end observability through Splunk + Prometheus + Dynatrace.

5️⃣ API URL Strategy (Real Production Style)

API	Gateway	URL	Hosted Where
Lending APIs	Azure APIM	https://api.deutschebank.com/lending/*	Azure
CRM APIs	AWS API Gateway	https://api.deutschebank.com/crm/*	AWS
Core Banking APIs	On-Prem Kong	https://api.deutschebank.com/core/*	On-Prem
Global Entry	Apigee X	https://api.deutschebank.com/*	Multi-cloud

All traffic uses the same top-level URL, but internally routes via gateway mappings.

6️⃣ Deployment & Governance Setup

a. Code + Config Deployment

• Infra as Code (IaC): Terraform or Ansible for all cloud resources

• API Config: GitOps with Azure DevOps or Jenkins pipelines

• Deployment Pattern: Canary or Blue-Green releases for gateway updates

• Change Governance: Controlled via CAB (Change Advisory Board)

b. Observability & Security

Concern	Tool	Implementation
Logging	Splunk / ELK	Correlated transaction IDs across clouds
Tracing	OpenTelemetry / Jaeger	API latency breakdown
Security	Azure AD + Ping + WAF	Centralized authentication & policy enforcement
Secrets	HashiCorp Vault / AWS Secrets Manager	Managed credentials

7️⃣ Typical Security & Compliance Measures

• No direct public IP exposure from on-prem or internal microservices

• All communication is over private links (ExpressRoute/DirectConnect)

• Mutual TLS + JWT validation between API Gateway and backend

• WAF (Web Application Firewall) at entry (Akamai / Azure Front Door)

• API rate limiting per client ID

• Continuous compliance monitoring for RBI / GDPR

8️⃣ How This Looks in Practice

🔹 External partner (FinTech / mobile app) calls api.deutschebank.com🔹 Global API Gateway (Apigee) authenticates & routes internally🔹 API policies (quota, token, schema validation) are applied centrally🔹 Data flows over private interconnect to cloud/on-prem microservices🔹 Observability tools track every hop with trace IDs🔹 Security teams get real-time dashboards in Splunk & Dynatrace

✅ Summary — What Happens in Real Production

Layer	Product / Tech	Hosted In	Function
Global API Gateway	Apigee X / Mulesoft	Azure + AWS	Unified entry & routing
Regional Gateway	Azure APIM / AWS API Gateway	Respective Clouds	Cloud-specific routing
Hybrid Connectivity	ExpressRoute, Direct Connect, VPN	Azure ↔ AWS ↔ On-Prem	Secure private network
Internal Mesh	Istio / Dapr	AKS / EKS	Service discovery & routing
Security Layer	Azure AD, Ping, WAF	Central	AuthN, AuthZ, rate limiting
Monitoring	Splunk, Dynatrace	Multi-region	Central observability
Governance	Terraform + GitOps	Global	Infra and config consistency