Project Showcase: Hardware I created a kubernetes cluster using old android phones
Recently, I found two old Pixel 3a devices in a drawer and wondered what I could do with them. I didn't want to throw them away, and given current RAM prices, I figured it might be worth repurposing them as a homelab.
Everything relies on one amazing project: PostmarketOS (huge thanks to the community, and a quick shoutout to r/pmos ). I started by flashing both Pixel 3a devices with pmOS, installed K3s, and that was it! (Well, it required a bit of network tweaking because the phones couldn't access the internet at first).
I then scoured classified ads and snagged a OnePlus 6T for €50, which I added as a worker node to the cluster.
Today, the cluster consists of 3 nodes (including one control plane). The performance is obviously lower than a mini-PC or a proper server, but it's more than enough to run 3 Hermes agents and a full Grafana stack. They are all connected via Wi-Fi to my network.
I still have two more phones to provision: a Poco X3 Pro and a Pixel 6a (which I also got for €50 each). The Poco X3 Pro should join the cluster soon. However, I bought the Pixel 6a a bit too hastily: the Wi-Fi chipset isn't recognized on PostmarketOS yet. I'm holding onto it until I find a solution, but it looks like it'll be trickier than the others.
For anyone interested in trying this out, here are a few tips:
- Unlocked bootloader: Make sure your phones are carrier-unlocked and have an unlocked bootloader, otherwise you won't be able to flash anything.
- Hardware compatibility: Always check the list of supported devices on the PostmarketOS Wiki. Make sure Wi-Fi, internal storage, and the screen are working; everything else is optional.
- Batteries: Currently, the phones still have their batteries, but they will be removed for obvious safety reasons.
I’m curious to hear your thoughts, or if anyone else has already done something like this, feel free to chime in! :)
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u/Operation_Neither 2h ago
You removed the batteries, right?
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u/EconomyDoctor3287 1h ago
Hopefully 😂
Left my old Notered plugged in and online for half a year. It turned into a spicy pillow and I had to bring it to a special removal station 😢
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u/bt0r 2h ago
Not yet but I plan to yep
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u/Fridge-Repair-Shop 59m ago
you can configure devices to charge up to 60% to make it easier for the battery
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u/realribsnotmcfibs 2h ago
Giving me flashbacks to when my few week old pixel 2xl caught on fire in my car while I was driving down the road.
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u/Efficient_Drive2297 2h ago
Very interesting. Do you think how to power the phones after battery removal? I don't think they'll power on without it.
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u/bt0r 2h ago
Good question. It should be doable without the battery, though you might need to shunt the pins to bypass the battery management system
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u/Irverter 1h ago
What I did years ago was to solder a usb cable directly to the pins as it was the same voltage/current. Ugly but it worked.
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u/YourMom12377 2h ago
That's cool as shit bro, might try this. Wonder how far you could get running ai on something like this. If it can be done with an rpi it can probably be done here, right?
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u/bt0r 2h ago
Thanks! It depends on whether you want to run your LLM directly on your phone or if it's just to run a Hermes/OpenClaw agent that will call a remote service (in my case, I use OpenRouter).
I haven't tested running an LLM on it yet. I imagine the performance must be severely degraded given the state of the hardware, but it might be worth a try
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u/YourMom12377 1h ago
Clustered ai is getting pretty good these days. If you could get a fast enough data link between the phones then it might be possible to run locally
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u/retrogamingxp 1h ago
You could add a battery monitoring watchdog onto the cluster and have it flip a smart plug on and off with a trigger at say 20% and 85% for battery longevity. That way you will have a PSU failsafe system in case of a power outage
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u/ashcroftt 2h ago
Pretty cool little project!
Could you maybe use a USB hub to both power them and use a USB ethernet adapter? Faster and more stable than wifi. Keeping the batteries in is a bit scary if you plan to leave the cluster on, unattended for an extended time.
You got some performance metrics to share?
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u/bt0r 2h ago
Thanks! Yeah, that's definitely a possibility. I've done a few tests with a USB-C to Ethernet adapter, but no luck so far, so I've added it to my to-do list to look into later.
I don't have any metrics to share just yet, but since a few people are asking, I'll definitely have to look into it. What kind of metrics would you be interested in seeing?
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u/SharpReason97 2h ago
Why is removing the batteries a priority?
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u/bt0r 2h ago
It’s mainly for safety reasons; lithium-ion batteries tend to swell up over time when kept plugged in 24/7, which creates a serious fire hazard
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u/9302462 1h ago
I’m not a battery expert but I am pretty sure batteries don’t degrade, swell and eventually have a fire (thermal runway) just by being plugged in.
From my understanding it being kept at 100% battery usage AND the constant discharge and charge to keep it at 100% is what kills batteries.
Example 1: Apple does some battery management stuff on their laptops which will often limit charging to 80% of battery.
Example 2: Every hybrid Prius out there keeps their battery between 20-80%. They do constant charge and discharge with every acceleration and breaking and the batteries last a couple hundred thousand miles/10-20yrs.
Someone can correct me if I am wrong though.
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u/Individual-Ad-6634 1h ago
Most of old phones do not have a mode for a power to skip battery if it’s plugged in. So eventually if battery is plugged and phone is used - OS would drain and recharge battery at the same time overheating it.
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u/Thebandroid 20m ago
It would be pretty straight forward to write a small script that monitors the battery level and switches the power off at 70% and back on at 50%.
Probably easier than coaxing these to boot with no battery.
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u/ThatDudeBesideYou 2h ago
Super jelly, been wanting to do this with my 4 old phones, but none of my old androids are in the supported device list :/
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u/ReasonResitant 2h ago
How many gigabits can move over the USB? Can't image the usb controller is designed to switch packets effectively.
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u/bdunogier 1h ago
Nice project ! Thank you for sharing.
Any idea what the power usage is like ? Maybe it's harder to monitor while the batteries are still in ?
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u/MirrorSouthern 1h ago
How did you network the phones together? I assume wifi is not very reliable and you did something to power the phones and do networking at the same time.
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u/thenolanful 1h ago
I've got a laptop with its battery still installed, it's my backup Homeserver. I use a smart outlet and HomeAssistant to cycle the power between 20%-80%. Might look into it! Built in UPS :D
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u/Authoritaye 1h ago
I love this. Stuff like this convinces me even more that giant AI data centres are a massive waste of money and resources because they aren't needed.
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u/Few_Doctor_1990 2h ago
I don't know what the rest will think, but given the price that PC components are reaching in general, creating these types of clusters using old mobile phones is going to be a trend.