headers

Recently I built the Seaberry, a Raspberry Pi Compute Module 4 mini ITX motherboard into a PC case (video coming soon...), and got the case power button, power LED, and activity LED all wired up to the Pi:

I used the GPIO and 14-pin header present on the Seaberry (which conveniently are identical to the headers on the official CM4 IO Board), and wound up with a fully functionality power button, power LED, and activity LED!

Here's how I did it:

Power button

To get the power button working, you need to connect the case's front panel 'power switch' connector to pins 12 and 14 (GLOBAL_EN and GND), as seen in the top middle of the above picture.

A colleague of mine found out that many static resource requests which should've been cached upstream by a CDN were not being cached, and the reason was an extra Vary http header being sent with the response—in this case Host.

It was hard to reproduce the issue, but in the end we found out it was related to Apache bug #58231. Basically, since we used some RewriteConds that evaluated the HTTP_HOST value before a RewriteRule, we ran into a bug where Apache would dump a Vary: Host header into the request response. When this was set, it effectively bypassed Varnish's cache, as well as our upstream CDN... and since it applied to all image, css, js, xml, etc. requests, we saw a lot of unexpected volume hitting the backend Apache servers.

To fix the issue, at least until the upstream bug is fixed in Debian, we decided to strip Host from the Vary header inside our Varnish default.vcl. Inside the vcl_backend_response, we added: