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I've recently taken over an environment using HAProxy, and I'm attempting to learn the config and what it all means, but I'm finding some aspects of it are not clear.

I think the above means that if host header begins with "" then use the cdn cdn_name, but I'm not totally sure. Can somebody confirm for me?


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It's defining an ACL with the name cdn_name, with the criteria hdr_beg(host) -i The criteria basically means that the HTTP Host: header begins with "" and it uses case-insensitive matching (the "-i" flag).

On it's own this doesn't actually do anything, but it will be used further down your config, where you will likely see something like this:

<something something> if cdn_name

What this does is if the client request uses a Host: header that begins with "", HAproxy will do whatever is defined in the <something something> bit of the config.

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