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how does the status monitoring website work under the hood? (programming.dev)

submitted 8 months ago* (last edited 8 months ago) by [email protected] to c/[email protected]

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I am talking about the services which let you monitor the status of a website whether the website is up and operational or down or under heavy load.

how do they work under the hood?

for example:

https://githubstatus.com

https://instatus.com

I am building something similar for monitoring my web projects.

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[–] [email protected] 8 points 8 months ago

Simple, do a GET or HEAD HTTP request to the monitored website with a 3 second timeout. If you get a 200 response code then you can assume the website is online and okay.

Why HEAD? Because:

if a URL might produce a large download, a HEAD request could read its Content-Length header to check the filesize without actually downloading the file. (...) A response to a HEAD method should not have a body

Using HEAD instead of GET will make it so your code doesn't have to actually download your frontpage to get the status. This will speed things up and reduce bandwidth usage.

Note: webservers may also return response codes for redirects, like 301 or 308 and and this case you usually do a follow up request to the URL the server pointed you at in order to check if it returns 200. Some HTTP libraries have built in ways to handling this and with a simple boolean they'll follow the redirect for you.