Implementing a Push‑Based Agent Registry Sync for Reliable MCP Updates

Amazon Bedrock AgentCore introduced a push‑based Agent Registry sync that ties MCP server changes directly to the central registry. The change replaces manual update steps with an event‑driven pipeline, ensuring that any new tool or schema modification is reflected in the registry as soon as the underlying UpdateAgentRuntime API call occurs. Practitioners benefit from up‑to‑date catalog data, fewer runtime errors, and a single source of truth that scales across accounts.

Why Push‑Based Agent Registry Sync Matters

Stale registry entries cause developers to call tools with outdated schemas, leading to runtime failures or silent workflow drift. By automating the propagation of changes, teams preserve trust in the catalog, avoid ad‑hoc discovery mechanisms, and keep governance processes consistent.

Architecture Overview

The solution stitches together five AWS services:

• AWS CloudTrail records every UpdateAgentRuntime call as a management event.
• Amazon EventBridge filters those events and forwards them to a central event bus.
• AWS Lambda runs the sync logic: it extracts the runtime ARN, builds the MCP server URL, obtains an OAuth token via AgentCore Identity, fetches the current tool list, diffs it against the registry, and updates the record if needed.
• AWS Agent Registry stores the authoritative MCP server metadata.
• AgentCore Identity handles token exchange without persisting secrets.

The pattern works in two deployment modes:

• Single‑account: All components live in the same AWS account, eliminating cross‑account forwarding.
• Multi‑account: Account A owns the registry, EventBridge rule, Lambda, and CloudTrail logs; Account B runs the MCP server and its Cognito OAuth provider. EventBridge forwards events from B to A, where the Lambda performs the sync.

Implementation Steps

1. Enable CloudTrail in the MCP server account to capture UpdateAgentRuntime API calls.
2. Create an EventBridge rule that matches those events and routes them to the central bus in the registry account (or the same account for single‑account setups).
3. Deploy a Lambda function in the registry account with the following responsibilities:
   • Parse the incoming event to obtain the runtime ARN.
   • Construct the MCP server endpoint dynamically.
   • Invoke AgentCore Identity to receive a bearer token.
   • Call the MCP server’s initialize and tools/list endpoints.
   • Compare the returned tool definitions with the existing registry entry.
   • Issue an update to the Agent Registry only when a difference is detected.
4. Grant the Lambda least‑privilege IAM permissions to call the MCP server, request tokens from AgentCore Identity, and invoke the Agent Registry update API.
5. Verify that a pre‑registered record for each MCP runtime exists in the registry; the Lambda updates existing records but does not create new ones.

Operational and Security Implications

From an operations perspective, the pipeline introduces continuous visibility into MCP changes via CloudTrail and EventBridge metrics. Teams should monitor event delivery success, Lambda error rates, and registry update latency to detect bottlenecks.

Security considerations include:

• Cross‑account EventBridge forwarding must be restricted to the specific event pattern to avoid unintended traffic.
• AgentCore Identity supplies short‑lived OAuth tokens, eliminating the need for static credentials in Lambda code.
• The Lambda’s IAM role should be scoped to the exact registry update API and the specific MCP endpoint URLs it needs to query.
• CloudTrail logs provide an immutable audit trail of who triggered a runtime update and when the sync occurred.

Related CloudNinjas coverage: AWS.

What This Means For Practitioners

Adopting the push‑based Agent Registry sync removes manual catalog maintenance, reduces error‑prone deployments, and aligns registry state with actual MCP runtimes across single or multiple accounts. Engineers should evaluate existing CloudTrail coverage, configure the EventBridge rule to match UpdateAgentRuntime events, and ensure the Lambda has the minimal permissions required. Monitoring the end‑to‑end flow will surface any gaps in event delivery or token acquisition, allowing teams to maintain a reliable, up‑to‑date service catalog without additional operational overhead.