Retrofit, don’t rebuild: Agentic overlays for transforming legacy enterprise services

This article explains how to retrofit legacy REST-based enterprise services with agentic capabilities using thin wrapper layers called agentic overlays, enabling participation in standardized Agent-to-Agent (A2A) communication.

• Agentic overlays transform A2A messages to REST payloads and expose REST endpoints as agent tasks without rewriting core business logic
• Two implementation patterns: within-application overlays for single-service agents and Amazon Bedrock AgentCore Gateway for multi-service enterprise workflows
• Provides reference implementation using Flask calculator service demonstrating message extraction, REST invocation, and JSON-RPC response building
• AgentCore capabilities including Identity, Observability, and Runtime simplify monitoring, authentication, and deployment of agentic overlays
• Eliminates need for parallel REST and A2A infrastructure stacks, reducing operational complexity and agent sprawl

Agentic overlays enable enterprises to adopt emerging A2A standards incrementally while preserving existing REST API investments and production-tested business logic.