Integration / API
APIInternalRestCloud-Native

Int-API-Internal

Problem

Internal applications and microservices need to exchange data or services securely, reliably, and in real-time without exposing their endpoints to the public internet.

Solution

Implement a Private API Gateway or internal Service Mesh within a private subnet to proxy, govern, and secure service-to-service communications. Standardize on modern synchronous APIs (REST, gRPC, or GraphQL) utilizing organizational authentication standards (OIDC/OAuth 2.0 or mutual TLS) and consistent schemas (OpenAPI, Protobuf).

Cloud Paradigm

API-First Design, Service-to-Service Connectivity, Service Mesh Architecture, Private API Gateways, and Zero Trust Architecture.

Implementation Guidelines

Solution Flow

Internal Request/Response Flow (Service-to-Service):

  1. Consumer Workload: A backend microservice or internal client initiates a synchronous HTTPS/gRPC request to a private endpoint.
  2. Private API Gateway / Service Mesh: The request is intercepted by the Private API Gateway or service mesh sidecar. This layer terminates mTLS, authenticates the consumer service identity, validates permissions, and enforces rate limits.
  3. Backend Workload (Provider): The provider microservice receives the authenticated request, executes the business logic, and returns the response.
  4. Mutual Verification: The response is encrypted and returned securely back to the consumer workload via the private network overlay.

Additional Details

  • Protocol & Format: Standardize on REST/JSON, gRPC/Protobuf, or GraphQL over HTTPS/HTTP2. Legacy integrations may use SOAP/XML over HTTPS if required, but should be isolated.

  • API Cataloging & Registry: Discoverability is critical. All internal APIs must be published in an internal developer portal (e.g., Backstage) with up-to-date OpenAPI/Swagger specifications or Protobuf definitions.

  • Microservices Orchestration: If a client request requires aggregating data from multiple services or performing complex transactional workflows, delegate orchestration to a dedicated orchestration layer or event-driven architecture rather than coupling services directly.

  • Observability: Implement distributed tracing (e.g., OpenTelemetry) across all internal API boundaries to facilitate rapid debugging of latency issues and cascading microservice failures.

  • Resilience Patterns: Implement retries with exponential backoff, circuit breakers, and fallback mechanisms on the consumer side to ensure high availability during temporary network blips.

Security Controls

  • Network Isolation: Internal APIs must only be accessible within the private network (VPC/VNet). Use Private Link endpoints (e.g., AWS VPC Endpoints, Azure Private Endpoints) to bridge connections securely across isolated VPCs/VNets without traversing the public internet.

  • Authentication & Authorisation: Enforce mutual TLS (mTLS) or OAuth 2.0 (Client Credentials grant) for all service-to-service communication to verify caller identity and authorize access. Avoid using shared static API keys.

  • Role-Based Access Control (RBAC): Apply fine-grained IAM policy authorization (e.g., Kubernetes NetworkPolicies, ServiceMesh AuthorizationPolicies) to ensure microservices can only call APIs they are explicitly authorized to access (Principle of Least Privilege).

  • Traffic Management & Throttling: Configure rate limiting, throttling, and burst quotas at the Private API Gateway to prevent cascading failures (e.g., retry storms) and shield backend systems from resource starvation.