Retrofit, don’t rebuild: Agentic overlays for transforming legacy enterprise services
TL;DR
AWS and Cisco authors propose agentic overlays: thin wrappers that let existing REST services show up as A2A-capable agents without rewriting the underlying business logic. The overlay translates A2A messages into REST payloads and maps REST responses back into JSON-RPC. REST endpoints can also be exposed as MCP-compatible tools. The reference implementation uses a Flask calculator service with an Agent Card, A2A routes, health endpoint, message extraction, auth-header forwarding, and internal REST calls.
Nauti's Take
This is one of the more practical enterprise AI patterns: do not turn every system into a new agent stack, make existing services speak the new protocols in a controlled way. That is how modernization should look when production systems cannot become a playground.
The catch: an overlay is not a magic layer. Weak REST contracts, fuzzy permissions and missing telemetry do not improve by being exposed to agents; they just become easier for agents to reach.
Briefingshow
Many enterprises already have stable REST services but no clean way to plug them into agent workflows. The overlay idea matters because it treats migration as an interface problem, not a rebuild. That can reduce risk, duplicate infrastructure and testing load, as long as governance, auth and observability are not treated as afterthoughts.
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