30 Minutes With MCP and flyctl

well, Cursor built I built the most basic MCP server for flyctl I could think of. It took 30 minutes. MCP, for those unaware, is the emerging standard protocol for connecting an LLM (or an app that drives an LLM in the cloud, like Claude Desktop) to

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Fly.io
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Kurt Mackey
•5 min read•intermediate•
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CDNClaudeJavaScriptJSONKong

Overview

The article discusses the implementation of a basic Model Context Protocol (MCP) server for the flyctl command-line tool, highlighting its utility in connecting large language models (LLMs) to various tools. It details the process of building the server in 30 minutes and showcases its functionality through real-world examples, including monitoring application health and logs.

What You'll Learn

1

How to build a basic MCP server for flyctl

2

Why MCP is essential for connecting LLMs to various tools

3

How to troubleshoot application health using MCP

Prerequisites & Requirements

  • Basic understanding of JSON and command-line tools
  • Access to flyctl and a suitable environment for running MCP servers

Key Questions Answered

What is the Model Context Protocol (MCP) and its purpose?
MCP is an emerging standard protocol designed to connect large language models (LLMs) to various tools and applications. It defines an exchange of JSON blobs, allowing LLMs to discover and utilize the tools exported by an MCP server, facilitating seamless integration and functionality.
How does the MCP server interact with flyctl commands?
The MCP server exposes specific flyctl commands, such as 'fly logs' and 'fly status', allowing LLMs to execute these commands and retrieve their outputs. This interaction enables the LLM to monitor application health and status through simple JSON exchanges.
What issues can be identified using the MCP server?
The MCP server can help identify critical issues such as memory usage problems in applications. For instance, it can reveal when a machine is in a 'critical' health status due to memory constraints, as demonstrated with the Bun process consuming excessive memory.

Key Statistics & Figures

Memory usage of Bun process
3.7GB
This was the memory consumption observed before the process was killed due to exceeding the 4GB limit allocated to the machine.
Number of machines running the application
10 machines
The application is distributed across multiple global regions to ensure low-latency access.

Technologies & Tools

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Protocol
Mcp
Used to connect LLMs to various tools and facilitate communication through JSON exchanges.
Command-line Tool
Flyctl
Utilized to manage and monitor applications deployed on Fly.io.
Runtime
Bun
The JavaScript runtime used for running the application in the example.

Key Actionable Insights

1
Implementing an MCP server can significantly streamline the integration of LLMs with various tools, enhancing automation and efficiency.
By utilizing MCP, developers can create a more interactive and responsive environment for LLMs, allowing them to perform tasks that would typically require manual intervention.
2
Regularly monitor application health using the MCP server to preemptively address potential issues.
The ability to retrieve logs and status updates through MCP can help identify and resolve performance bottlenecks before they escalate into critical failures.
3
Consider using JSON modes for commands in flyctl to facilitate easier automation.
This approach can enhance the usability of commands within scripts and automated workflows, making it simpler to integrate with other systems.

Common Pitfalls

1
Running an MCP server locally can pose security risks, especially when allowing LLMs to execute commands on the host machine.
To mitigate this risk, it's advisable to run such servers in isolated environments to prevent unauthorized access or execution of harmful commands.

Related Concepts

Model Context Protocol (mcp)
Large Language Models (llms)
Command-line Tools
Application Health Monitoring