A spinner appeared over the text INSTALL, stayed there several minutes, and then this overlay appeared:
Failed to install add-on
Can’t install homeassistant/aarch64-addon-configurator:5.8.0: 500 Server Error for http+docker://localhost/v1.47/images/create?tag=5.8.0&fromImage=homeassistant%2Faarch64-addon-configurator&platform=linux%2Farm64: Internal Server Error ("unknown: <html><body><h1>408 Request Time-out</h1> Your browser didn’t send a complete request in time. </body></html> ")
I tried installing the add-on three times over the course of about half an hour, with the same result each time.
From Nov 2018 - Apr 2024, many users encountered a 408 Request Time-out error like mine, but with slightly different wording: Internal Server Error ("error parsing HTTP 408 response body: invalid character '<' looking for beginning of value: "<html><body><h1>408 Request Time-out</h1>\nYour browser didn't send a complete request in time.\n</body></html>\n"")
In Nov 2024, a user encountered the exact same error as me.
Problem may be due to MTU size conflict with Docker CDN? If Home Assistant is on Armbian, fix by enabling MTU probing: sudo sysctl -w net.ipv4.tcp_mtu_probing=1
If we assume all the above bug reports were caused by the same underlying issue, which seems to be to do with network connectivity, we can infer that:
Between 5 Apr 2024 - 5 Nov 2024, a string or statement in HA or one of its dependencies was substituted as follows, changing the way HA reported this error to the user: s/error parsing HTTP 408 response body: invalid character '<' looking for beginning of value/unknown/
Individual instances of the error might be resolvable through network configuration changes.
When time permits, I will test this hypothesis on my install and report back.
Tentative conclusion
Subject to corroboration of hypothesis above: Home Assistant should probably check, at install time, for any network configurations that conflict with its expectations, and automatically adjust its expectations (e.g. MTU size) to avoid inconveniencing the user later on. If it cannot do so, it should warn the user to make the necessary changes manually.
Setting my router’s PPPoE MTU to 1500 bytes resolved the problem.
Notes
My router’s WAN (PPPoE) interface MTU was set to 1508 bytes. My ISP supports jumbo frames (1900 bytes), so I did not expect a 1508-byte MTU to cause problems. Attempting to install File Editor was the first time I noticed a problem. Maybe the Docker CDN requires smaller packets.
Suggestion
HA should check, upon install, for MTU configuration incompatibilities on the network path between the HA instance and the Docker CDN.