For a few years I put mine inside an IKEA FRIHETEN sofa (the kind that just pulls†).
Pros:
- easy access
- completely invisible save for 1 power wire + 1 fiber (WAN) + 1 eth (LAN)††
- structure allows easy cable routing out (worst case you punch a hole on the thin low-end)
- easy layout/cable routing inside
- noise reduction for free
- doubles as warming in winter a seated butt is never cold
- spouse enjoys zero blinkenlights
- spouse didn't even notice I bought a UPS + a disk bay
Cons:
- a bit uncomfortable to manipulate things inside
- vibrations (as in, spinning rust may not like it) when sitting/seated/opening/closing
- heat (was surprisingly OK, not worse than a closet)
- accidental spillage risks (but mostly OK as design makes it flow around, not inside the container, worst case: put some raisers under hardware)
- accidental wire pull e.g when unsuspecting spouse is moving furniture around for housecleaning (give'em some slack)
I had a similar thought about the IKEA KIVIK sofa (non-sleeper variants), which has wide boxy armrests that are open to the underside, and could fit towers of little SFF PCs, or maybe rackmount gear sideways. There's also space underneath the seat, where rackmount gear could fit.
One of the reasons I didn't do this was I didn't want a fire with sofa fuel right above/around it. I wasn't concerned about the servers, but a bit about the UPS. Sheet metal lining of the area, with good venting if the UPS battery type could leak gases, I'd feel a bit better about, but too much work. So the gear ended up away from upholstery, in rack/shelving, where I could keep an eye on it.
Unfortunately no. I moved its content out when I added big spinning rust to the system.
Although I did some yelling^Wsitting test and found it to be surprisingly impervious it was not so much to the furniture moving scenario.
That, and the UPS being the unlikely-but-real fire hazard. Old man printers-and-shotguns, y'know.
(disclaimer: I'm an internet rando, not a fireman, seek professional guidance)
But then again it's going to be a fire hazard anywhere except in a fireproof enclosure: it may give warm fuzzies that it's kept in sight but a) these things pack a ton of energy and would burn fast and long; b) fire propagates stupidly quick in residential locations; c) you're not looking at it 24/7, far from it.
In a way, ok the whole thing is fuel surrounding it, but this fuel first needs to be consumed for the fire to fully break out. IKEA products are also already designed with some form of fireproofness in mind (e.g textile and foam won't burn as easily as you'd think). It won't resist long but it may comparatively give a few seconds delay before it makes it worse and breaks out to the whole room.
This time could be improved by lining the interior with fire retardant panels, including the underside of the sitting area. Given the roomy boxy shape of it it should be quite easy to do. If done right it could even be near-airtight, so that fire could delay/choke itself due to lack of O2. This would need active ventilation for thermals, but it could shut itself down on a reasonable heuristic indicating trouble. Heck now I'm thinking automatically injecting CO2/spraying water droplets to further quench. Oh, an engineer's imagination running wild.
The most recommended - and much cheaper - investment though would be a fire/smoke detector, as whether in sight or not, with such fires the most sensible general recommendation one could make would be:
a) be alerted as early
as possible, preferably before any flame/smoke is visible.
b) immediately get out, like, RIGHT NOW. Think after. Life is the one thing of true value that cannot be replaced.
I'm not kidding. You have ~30s tops from the beep to get the whole family out. After that smoke is irrevocably incapacitating and flashover is only a short minute away.
Then watch it again, roleplaying yourself having to be woken up by the alarm, then having to navigate through smoke, heat, and panic to get the spouse and kids out. These 30s are going to be awfully shorter IRL than they already appear watching the video.
End of interlude.
Ventilation was passive yet OK, temps were higher that open air of course but good. A thing that helped is that I did not put your run-of-the-mill Xeon server blade in there, that would be dumb, although it would make for a nice synesthetic experience when watching Top Gun.
So I aimed for passive cooled stuff (ISP ONT+router, RPis, bunch of USB portable SSDs and HDDs) or active but low thermal requirements (headless Mac Mini, 5-disk bay, UPS). I monitored temps and they were well within parameters, I've seen much worse numbers in actual server rooms. The most noisy things were the 3.5" 7200rpm drives spinning up and seeking (constant rotation was inaudible) and the disk bay fan (lousy unlubricated bearing).
Given the side panel size, pretty sure one could hack active ventilation with big near-silent fans.
For a few years I put mine inside an IKEA FRIHETEN sofa (the kind that just pulls†).
† https://www.ikea.com/us/en/images/products/friheten-sleeper-...†† that I conveniently routed to a corner in the back then hidden in the wall to the nearest plugs, so really invisible in practice.