---
title: "Blocking bad bots using Relayd"
category: 
- bsd
- update
- bsd-update
abstract: 
date: 2023-12-10T12:27:54+02:00
---
The bane of existence for most of small pages: web crawlers.
They create most traffic this site sees and makes my [site stats](https://michal.sapka.me/site/info/#site-stats) overly optimistic.
We can go with [robots.txt](https://en.wikipedia.org/wiki/Robots_Exclusion_Protocol), but what if it's not enough?
I can tell a valuable bot to not index some part of my site, but:  
a) some bots ignore it  
a) what if I don't want some bots to even have the chance to ask?  

Get that SEO scanning and LLM training out of here!

## Blocking crawlers

The rest of this guide assumes webstack: Relayd and Httpd.
Relayd is great and since it works on higher level than pf, we can read headers. Luckily, those crawlers send usable "User-Agents" which we can block.

First, let's see who uses my site the most. Assuming you use "forwarded" style for logs, we can do:

{{<highlight shell>}}
awk -F '"' '{print $6}' <path to log file> | sort | uniq -c | sort
{{</highlight>}}

Then we need to manually select agents we want to block. It won't be easy, as the strings are long and contain a lot of unnecessary information - which includes plain lies. You need to define which part of the full Uer-Agent is common and can be used for blocking.

Then we can create block rules in a Relayd protocol. Relayd doesn't use regexp, and instead allows using case-sensitive Lua globs. Stars will match everything.

{{<highlight shell>}}
block request method "GET" header "User-Agent" value "*<common part>*"
{{</highlight>}}

Remember that config assumes last-one-wins, so the block rules should be the last matching. I just put those end the end of my config. You can create a `block quick...` rule if you want - it will short-circuit the entire protocol.

Therefore, my "https" protocol now has a series of blocks:

{{<highlight shell "linenos=inline">}}
http protocol "https" {
# most of the procol omitted
    block request method "GET" header "User-Agent" value "*Bytespider*"
    block request method "GET" header "User-Agent" value "*ahrefs*"
    block request method "GET" header "User-Agent" value "*censys*"
    block request method "GET" header "User-Agent" value "*commoncrawl*"
    block request method "GET" header "User-Agent" value "*dataforseo*"
    block request method "GET" header "User-Agent" value "*mj12*"
    block request method "GET" header "User-Agent" value "*semrush*"
    block request method "GET" header "User-Agent" value "*webmeup*"
    block request method "GET" header "User-Agent" value "*zoominfo*"
}
{{</highlight>}}

*(using globs was proposed to me on [OpenBSD mailing list](https://marc.info/?l=openbsd-misc&m=170206886109953&w=2)*