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[Doc] Restructure README Usage section to align heading granularity #316

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koic merged 1 commit into from
Apr 15, 2026
+25 −14
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[Doc] Restructure README Usage section to align heading granularity #316

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39 changes: 25 additions & 14 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -104,7 +104,24 @@ $ ruby examples/stdio_server.rb
{"jsonrpc":"2.0","id":"3","method":"tools/call","params":{"name":"example_tool","arguments":{"message":"Hello"}}}
```

#### Rails (mount)
#### Streamable HTTP Transport

`MCP::Server::Transports::StreamableHTTPTransport` is a standard Rack app, so it can be mounted in any Rack-compatible framework.
The following examples show two common integration styles in Rails.

> [!IMPORTANT]
> `MCP::Server::Transports::StreamableHTTPTransport` stores session and SSE stream state in memory,
> so it must run in a single process. Use a single-process server (e.g., Puma with `workers 0`).
> Multi-process configurations (Unicorn, or Puma with `workers > 0`) fork separate processes that
> do not share memory, which breaks session management and SSE connections.
>
> When running multiple server instances behind a load balancer, configure your load balancer to use
> sticky sessions (session affinity) so that requests with the same `Mcp-Session-Id` header are always
> routed to the same instance.
>
> Stateless mode (`stateless: true`) does not use sessions and works with any server configuration.

##### Rails (mount)

`StreamableHTTPTransport` is a Rack app that can be mounted directly in Rails routes:

Expand All @@ -125,7 +142,13 @@ Rails.application.routes.draw do
end
```

#### Rails (controller)
`mount` directs all HTTP methods on `/mcp` to the transport. `StreamableHTTPTransport` internally dispatches
`POST` (client-to-server JSON-RPC messages, with responses optionally streamed via SSE),
`GET` (optional standalone SSE stream for server-to-client messages), and `DELETE` (session termination) per
the [MCP Streamable HTTP transport spec](https://modelcontextprotocol.io/specification/latest/basic/transports#streamable-http),
so no additional route configuration is needed.

##### Rails (controller)

While the mount approach creates a single server at boot time, the controller approach creates a new server per request.
This allows you to customize tools, prompts, or configuration based on the request (e.g., different tools per route).
Expand Down Expand Up @@ -153,18 +176,6 @@ class McpController < ActionController::API
end
```

> [!IMPORTANT]
> `MCP::Server::Transports::StreamableHTTPTransport` stores session and SSE stream state in memory,
> so it must run in a single process. Use a single-process server (e.g., Puma with `workers 0`).
> Multi-process configurations (Unicorn, or Puma with `workers > 0`) fork separate processes that
> do not share memory, which breaks session management and SSE connections.
>
> When running multiple server instances behind a load balancer, configure your load balancer to use
> sticky sessions (session affinity) so that requests with the same `Mcp-Session-Id` header are always
> routed to the same instance.
>
> Stateless mode (`stateless: true`) does not use sessions and works with any server configuration.

### Configuration

The gem can be configured using the `MCP.configure` block:
Expand Down