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Hacker News·Jun 16·5 min read
TIL: You can make HTTP requests without curl using Bash /dev/TCP
TL;DR
When needing to check connectivity between Docker containers without curl or wget, a method using Bash's /dev/tcp can be employed. By manually crafting an HTTP request through Bash, engineers can verify service health without additional tools.
✦ Why It Matters
Engineers can use Bash's /dev/tcp to perform HTTP requests in environments lacking standard tools.
Key Takeaways
- Use /dev/tcp for HTTP requests in minimal Docker images.
- Manually craft requests to check service health without curl.
- Add custom headers by including lines before the request's end.
- Understand that /dev/tcp is a Bash feature, not a physical file.
Full Summary
In scenarios where minimal Docker images lack common tools like curl or wget, engineers may struggle to perform HTTP requests. However, Bash provides a unique feature through /dev/tcp, allowing users to open TCP connections directly from the shell.
By redirecting to /dev/tcp followed by the hostname and port, users can send raw HTTP requests, including custom headers. For example, to check a service's health, one can send a GET request to the appropriate endpoint.
The response includes the status line, headers, and body, all printed to the console. This method is particularly useful in lightweight environments where traditional tools are unavailable.
Understanding this technique can enhance troubleshooting and service verification in containerized applications.