Building an Enterprise MCP Gateway: A System Design Perspective
Preface
The idea for this blog came from a simple question: how does an agent discover the right tools when an enterprise has multiple MCP servers across different domains, each exposing dozens of tools? Connecting the agent to every MCP and letting it figure things out doesn’t feel scalable. That led me to explore the design of an Enterprise MCP Gateway for semantic tool discovery and routing.
The idea of AWS AgentCore Gateway gave me the motivation and knowledge to attempt a System Design approach for such implementation.
Introduction
Model Context Protocol (MCP) has changed the way AI agents interact with enterprise capabilities.
Instead of building custom integrations between every agent and every enterprise system, an organization can expose capabilities through MCP servers. An agent can then discover and invoke tools through a standardized protocol.
That works well when the architecture looks like this:
Agent -> MCP Client -> MCP Server -> Tools
But enterprise environments don’t have one MCP server. They may eventually have hundreds of MCP servers and thousands of tools:
At this scale, a new problem emerges:
How does the agent find the right capability across thousands of tools and route the request to the correct MCP server?
MCP itself provides the protocol for communicating with a known MCP server and discovering its capabilities. It does not define an enterprise-wide semantic tool discovery, authorization, cataloging, synchronization, or routing system.
That is where an Enterprise MCP Gateway comes in.
The gateway is therefore much more than a reverse proxy. It becomes a capability control plane and runtime gateway for agent-to-enterprise interactions.
What are we actually trying to build?
I would define the enterprise MCP gateway around five core responsibilities:
- MCP target management
- Capability discovery and semantic tool search
- Authentication and authorization
- Deterministic tool-to-server routing
- Capability synchronization and lifecycle management
There are also important non-functional requirements:
- low latency
- horizontal scalability
- high availability
- operational resilience
- observability
- auditability
- security
- eventual consistency of the capability catalog
- isolation between MCP targets
The resulting architecture looks like this:
The important architectural characteristic is. This is the foundation of the design.
The gateway behaves as an MCP Server toward the agent and as an MCP Client toward downstream MCP servers.
Northbound and Southbound MCP
From the agent’s perspective, there is only one MCP endpoint. The gateway hides the complexity of the enterprise MCP landscape. Internally, however, it maintains connections to multiple MCP servers as shown above.
So the gateway effectively has two faces: Northbound (Gateway = MCP Server) and Southbound (Gateway = MCP Client)
This allows the agent to interact with one logical MCP endpoint while the gateway handles discovery and routing behind the scenes.
The Control Plane
I would separate the gateway into a control plane and a data plane.
The control plane manages relatively slow-changing information:
The data plane handles high-volume runtime traffic:
This separation is important for scalability.
A synchronization operation that takes a few seconds should never block a runtime tools/call request.
MCP Target Registry
The first component of the control plane is the MCP Target Registry.
A target represents a downstream MCP server.
For example:
The registry answers:
What MCP servers exist and how do I connect to them?
It does not need to contain every detail required for semantic search. That belongs in the capability catalog.
Capability catalog
When a target is registered, the gateway connects to the MCP server and discovers its capabilities.
For example:
Instead of treating these merely as tool names, I would build an enriched capability representation.
For example:
Why hierarchical discovery matters
At enterprise scale, searching 20,000 tools for every request isn’t ideal. So, I would prefer a Hierarchy.
Lets take a Financial Services example:
This allows discovery to happen progressively. This hierarchical approach also improves both latency and relevance.
Semantic tool search
The semantic search is not something the downstream MCP servers do. It is a capability of the gateway’s control/discovery plane, exposed to the agent through the gateway’s single, virtual MCP server interface.
This is perhaps the most important design question in an enterprise MCP gateway. The downstream MCP servers know about their own tools. They don’t know about the complete enterprise tool landscape.
Suppose the agent asks:
“Can I book this trade against legal entity ABC?”
Which MCP server should the agent contact?
It shouldn’t have to know!
This is precisely where the semantic discovery layer of the MCP Gateway comes in. The gateway maintains a global capability catalog containing the tools exposed by all registered MCP targets.
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Conceptually:
The gateway as a Virtual Server is important. The gateway presents one logical MCP server to the agent. Therefore, the gateway effectively creates a virtual enterprise-wide MCP server.
However, I would be careful with the terminology:
The gateway is not magically merging the downstream MCP servers into one physical server. It is aggregating their capabilities into one logical MCP endpoint. The capability catalog is what makes that abstraction possible. The semantic search layer sits behind that virtual MCP interface.
The downstream MCP server’s job is not discovery across the enterprise. Its job is to expose and execute capabilities belonging to its own domain/system.
Think of the gateway as an enterprise capability directory + router, while each MCP server is the actual capability provider.
MCP target registration and synchronization
The capability catalog cannot be static. MCP servers evolve. The gateway therefore needs a synchronization service. The synchronization service compares the current MCP capability definition with the stored version.
For detecting schema changes, a normalized tool definition can be hashed. This avoids unnecessarily regenerating embeddings for thousands of unchanged tools.
e.g.
tool_hash =
SHA256(
name +
description +
inputSchema +
annotations
)How should synchronization be triggered?
An enterprise MCP Gateway maintains a centralized capability catalog containing information about MCP servers and their tools. However, MCP servers are not static. Tools can be added, removed, renamed, or have their descriptions and schemas modified.
Therefore, the gateway needs a reliable synchronization strategy.
A production-grade design should use three mechanisms together:
- Explicit synchronization
- Event-driven synchronization
- Periodic reconciliation
1. Explicit Synchronization
Explicit synchronization is an on-demand mechanism.
When an MCP server is initially registered, or when an administrator knows that the server has changed, the gateway can explicitly synchronize its capabilities.
The synchronization worker retrieves the current tool definitions and compares them with the gateway’s stored version.
2. Event-Driven Synchronization
For a large enterprise, relying only on explicit synchronization doesn’t scale operationally.
Suppose 500 MCP servers are managed by different teams. A team deploys a new tool but forgets to notify the gateway.
A better approach is to make synchronization event-driven.
Typical events could be:
MCP_TARGET_REGISTERED
MCP_TARGET_UPDATED
MCP_TARGET_DECOMMISSIONED
TOOL_ADDED
TOOL_UPDATED
TOOL_REMOVED
The event should ideally contain enough information for the gateway to identify the affected target, for example:
{
target_id: "booking-mcp-prod",
event_type: "TOOL_UPDATED",
version: "v42"
}The synchronization worker can then retrieve the authoritative tool definition from the MCP server and update the catalog.
I prefer this over putting the entire tool definition into Kafka because the MCP server remains the source of truth.
3. Periodic Reconciliation (optional / Good-to-have)
Event-driven synchronization improves freshness, but it cannot guarantee correctness by itself.
Distributed systems fail.
An event may be:
- Lost
- Incorrectly generated
- Generated before a deployment completes
- Consumed after a temporary outage
- Generated by one system but not another
Therefore, I would always introduce periodic reconciliation.
Gateway Observability
Monitor the gateway at three levels.
Gateway metrics
Request rate
P50 latency
P95 latency
P99 latency
Error rate
Authentication failures
Authorization failures
ThroughputMCP target metrics
Availability
Latency
Timeouts
Error rate
Circuit breaker state
Tool failure rate
Connection failuresSearch metrics
Search latency
Zero-result queries
Top-K relevance
Tool-selection accuracy
Index freshness
Stale capability count
Search failuresLatency Design
A critical design principle is:
Never perform enterprise-wide MCP discovery synchronously at runtime.
A bad design would be:
This creates unacceptable latency and makes the gateway dependent on the availability of every MCP server.
Instead: The gateway searches its pre-built capability index.
The downstream MCP server is contacted only after the gateway has identified the target.
Failure Handling
In an enterprise MCP Gateway, failure handling is not simply about adding retries and timeouts. The gateway sits between an autonomous agent and potentially hundreds of enterprise capabilities, so a failure in one component must be contained, observable, recoverable, and most importantly must not result in an unsafe action.
Failures will occur across the control plane, data plane, search layer, downstream MCP servers, networks, identity systems, and even the AI agent itself.
1. First, Separate Control-Plane and Data-Plane Failures
A failure in the control plane should not automatically take down the data plane. For example, suppose the embedding service is temporarily unavailable. The gateway should not suddenly stop an already-known tool from being invoked.
This is one reason why asynchronous synchronization and pre-built indexes are so important.
Lastly, briefly touching on Security Architecture
Security should exist at multiple levels.
Use enterprise identity and OAuth/token-based authentication.
Authorization should be performed both: During Discovery and during Invocation.
This is important because:
Discovering a tool does not mean the caller is authorized to execute it.
Conclusion
The MCP Gateway becomes the central intelligence layer that connects an agent to a growing ecosystem of MCP servers. Its Control Plane handles registration, capability synchronization, metadata, and semantic indexing, while the Data Plane uses that context to discover and route the right tools based on the agent’s intent and domain semantics. This decouples the agent from individual MCP servers and lets new domain capabilities plug into the enterprise without changing the agent itself.
