AgentCore MCP Reverse Connector on Amazon EKS

This project deploys a minimal MCP-compatible Python tool server on Amazon EKS. The pod opens an outbound secure WebSocket connection to AGENTCORE_GATEWAY_ENDPOINT and authenticates with AGENTCORE_AUTH_TOKEN.

The connector implements the MCP JSON-RPC methods required for tool discovery and invocation:

• initialize

• tools/list

• tools/call

• ping

It exposes two tools:

• get_system_info

• echo_data

Architecture Note

Amazon Bedrock AgentCore Gateway documentation describes Gateway as an MCP endpoint for agents and as a service that can invoke configured targets such as Lambda, OpenAPI, Smithy, and remote MCP server endpoints. A reverse dial-out WebSocket connector requires your AgentCore Gateway endpoint, relay, or fronting service to support a persistent outbound WebSocket contract.

This implementation assumes that contract exists and that the gateway sends MCP JSON-RPC request messages over the WebSocket. If your Gateway is configured for a standard MCP server target instead, expose this server through a normal MCP HTTP/SSE endpoint or put it behind an internal/external load balancer and register that endpoint with AgentCore.

Project Tree

agentcore-mcp-eks/
├── .dockerignore
├── .gitignore
├── Dockerfile
├── Makefile
├── README.md
├── k8s/
│   ├── base/
│   │   ├── configmap.yaml
│   │   ├── deployment.yaml
│   │   ├── hpa.yaml
│   │   ├── kustomization.yaml
│   │   ├── namespace.yaml
│   │   ├── networkpolicy.yaml
│   │   ├── pdb.yaml
│   │   ├── service.yaml
│   │   └── serviceaccount.yaml
│   └── examples/
│       └── secret.example.yaml
├── requirements.txt
└── src/
    ├── pyproject.toml
    └── agentcore_mcp_server/
        ├── __init__.py
        ├── __main__.py
        ├── config.py
        ├── connector.py
        ├── health.py
        ├── protocol.py
        └── tools.py

Prerequisites

• An existing Amazon EKS cluster with worker nodes that can egress to the AgentCore Gateway endpoint over TCP 443.

• aws CLI configured for the target AWS account.

• kubectl configured for the EKS cluster.

• Docker or another OCI-compatible image builder.

• Terraform or your preferred IaC workflow if you still need to create EKS.

• A container registry, for example Amazon ECR or GitHub Container Registry.

• Kubernetes Metrics Server if you want the HPA to scale on CPU metrics.

• Known values for:

  • AGENTCORE_GATEWAY_ENDPOINT

  • AGENTCORE_AUTH_TOKEN

Build and Publish

Set your image name:

cd agentcore-mcp-eks
export IMAGE="123456789012.dkr.ecr.us-east-1.amazonaws.com/agentcore-mcp-server"
export TAG="0.1.0"

Build and push:

docker build -t "${IMAGE}:${TAG}" .
docker push "${IMAGE}:${TAG}"

Update the Deployment image in k8s/base/deployment.yaml or use Kustomize:

kubectl kustomize k8s/base

Configure Kubernetes

Create the namespace first so the Secret can be created safely:

kubectl apply -f k8s/base/namespace.yaml

Create the auth token secret without storing a real token in Git:

kubectl -n mcp-system create secret generic agentcore-mcp-secret \
  --from-literal=AGENTCORE_AUTH_TOKEN='replace-with-real-token'

Set the gateway endpoint by editing k8s/base/configmap.yaml:

data:
  AGENTCORE_GATEWAY_ENDPOINT: "wss://gateway.example.com/mcp/reverse"
  MCP_SERVER_NAME: "eks-agentcore-mcp"

If you want to use the example Secret manifest instead, copy k8s/examples/secret.example.yaml, replace the placeholder, and apply it from a secure private location.

Deploy

Apply the manifests:

kubectl apply -k k8s/base

Check rollout:

kubectl -n mcp-system rollout status deployment/agentcore-mcp-server
kubectl -n mcp-system get pods -l app.kubernetes.io/name=agentcore-mcp-server

Tail logs:

kubectl -n mcp-system logs deployment/agentcore-mcp-server -f

Operational Checks

Port-forward the internal service for health checks:

kubectl -n mcp-system port-forward svc/agentcore-mcp-server 8080:8080
curl -fsS http://127.0.0.1:8080/healthz
curl -fsS http://127.0.0.1:8080/readyz

Expected behavior:

• /healthz returns 200 when the process is running.

• /readyz returns 200 only after the WebSocket connection to the gateway is established.

Troubleshooting Gateway Connectivity

Check pod environment wiring without printing the token:

kubectl -n mcp-system describe pod -l app.kubernetes.io/name=agentcore-mcp-server

Look for connector log messages:

kubectl -n mcp-system logs deployment/agentcore-mcp-server --tail=200

Common issues:

• AGENTCORE_GATEWAY_ENDPOINT is required: the ConfigMap is missing or the key is misspelled.

• AGENTCORE_AUTH_TOKEN is required: the Secret is missing or the key is misspelled.

• Repeated connect failures: verify the endpoint starts with wss://, DNS resolves from inside the cluster, and node security groups/NACLs permit egress to TCP 443.

• Authentication failures: rotate the Secret and restart the Deployment with kubectl -n mcp-system rollout restart deployment/agentcore-mcp-server.

• Readiness never becomes healthy: confirm the gateway supports the reverse WebSocket connector contract and accepts MCP JSON-RPC messages over the socket.

• NetworkPolicy blocks traffic: start by applying the Deployment without networkpolicy.yaml, confirm connectivity, then reapply and tighten egress for your CNI.

Run an in-cluster DNS/connectivity test:

kubectl -n mcp-system run netcheck --rm -it --restart=Never \
  --image=curlimages/curl:8.10.1 -- sh

Then inside the shell:

nslookup gateway.example.com
curl -vk https://gateway.example.com/

Security Notes

• Do not commit real tokens. Use Kubernetes Secrets, External Secrets Operator, AWS Secrets Manager, or Sealed Secrets.

• The container runs as a non-root user with a read-only root filesystem and dropped Linux capabilities.

• The default Service is ClusterIP; there is no public inbound endpoint because the server dials out.

• The example NetworkPolicy allows DNS and outbound HTTPS. For strict FQDN egress controls, use a CNI that supports FQDN policies such as Cilium or Calico Enterprise and restrict access to the exact AgentCore Gateway hostname.

• Tool input schemas are fully inlined and do not use JSON Schema $ref or $defs.

References

• Amazon Bedrock AgentCore Gateway overview

• AgentCore Gateway MCP usage

• AgentCore Gateway MCP server targets

• MCP Python SDK package