Would it be possible to run Pi-hole, Octoprint and Home Assistant on the same RPi 3 mod. B?

You do not want Octoprint on a machine that is busy. Otherwise you have load spikes that cause Octoprint to not be able to send the move-commands (gcode) as fast as the printer executes the movements. This problem is pronounced with faster printers and slicers that break up arcs into small straight lines (which is practically all slicers). Otherwise your printer stutters because it has to take small breaks to wait for the next command from octoprint.

This right here.

Octoprint (or any other 3d printer controller for that matter) should not run on a device which is doing unpredictable stuff at the same time.

Op was so preoccupied with whether or not they could, they didn’t stop to think if they should.

I definitely get where they're coming from though. It seems inefficient to have all these services running on separate hardware where each service might only be using 25% of the capability (not necessarily in OPs case with the Pi3B) of the device and needing three separate electrical outlets to do some real basic computing.

I've been very casually exploring Proxmox on a micro Optiplex but haven't had the time or need to jump in head first quite yet since things are still working. The real downside is that your single piece of hardware becomes a failure point for everything but as this is just home hobby stuff and not a big business, it's not really that big of an issue.

I think it's possible to run everything in the same RPi 3b, however I think it will not be smooth, cause there is only 1GB of ram available...

I think the best is one device for each service, however I know that sometime we can't afford that, so I think you need at least 1 device for Pi-Hole and Octoprint, and another to the Home Assistant

Definitely agree they should be split up if possible. Octoprint and Home Assistant are both rather demanding on a Pi, particularly the Pi 3B.

I would however opt to run Pi-Hole on the Home Assistant device as there is a plugin built in for it, and Home Assistant is the kind of thing you would be more likely to leave on at all times.
- Just as a tangent, definitely get an SSD for whatever device is running HomeAssistant and set it as the boot drive as the constant writes will cause your SD card to explode in a huge fireball after not too long.
Thanks for the answer!

Possible: yes

Recommend: absolutely not

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters	More Letters
DNS	Domain Name Service/System
HA	Home Assistant automation software
~	High Availability
PiHole	Network-wide ad-blocker (DNS sinkhole)
RPi	Raspberry Pi brand of SBC
SBC	Single-Board Computer
SSD	Solid State Drive mass storage
VPN	Virtual Private Network

6 acronyms in this thread; the most compressed thread commented on today has 9 acronyms.

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Wouldn't put pihole or any other mission critical network service on a Pi, unless there's some kind of fallback.

Why not and what would you recommend instead?
- IMO pi is perfect fit for pihole (low power and silent), but since its mission critical you want 2 devices running pihole. If one is down the other one will still be available. I have one pihole running on the server that runs all other services (including home assistant), and 2nd pihole on rpi4. Then I have another pi4 for 3D printer
  
  Running pohole and homeassistant on the same device is not a problem for sure, but not sure about octoprint since it is using USB serial connection while printer is active (can be 12h+). Maybe it can work, but I wouldnt use 3D printer computer for anything else
- Not OP but loss of the Pi results in loss of network connectivity. A headache if you're home and never doing anything time-critical on the network. A disaster if you or anyone else is dependent on the network for anything time-sensitive (virtual doctors appointment, work call, etc), or you're away from home and unable to directly VPN to your router to reconfigure DNS settings.
- As some others mentioned, when the DNS goes down (which pihole is) your whole network is down. With the fragility (and slowness) of the PI, it'd be more likely it will go down, sooner than later.
  
  Considering the cost, a good alternative, imho, would be some sort of thin client, with an energy efficient CPU. So, instead of getting 2-3 PIs, better get one of these TCs, while keeping your PI as a DNS backup solution.
You could say that with most any hardware. You could have a dedicated server fail and have your network be down till you got another instance up or have a "fall back" kick in.

What makes Rasp Pi so much more unstable? If anything a couple PIs are definitely a cheaper solution compared to other hardware like you are suggesting?
- couple of Pis are cheaper
  
  Are they thou? In my region the 4Bs are selling at around 60 bucks (no case, no SD)... A "couple" of them (including some for backup and HA and Octoprint) would mean at least 4 of them, totalling at 240 bucks (or 300 with SD). For that money, one could get two (or even three) more-than-capable thin clients.

My home-assistant installation alone is too much for my Raspberry Pi 3. It depends entirely on how much data it's processing and needing to keep in memory.

Octoprint needs to respond in a timely manner, so you will want to have the system mostly idle (at least below 60 percent CPU at all times), preferably octoprint should be the only thing running on the system unless it's rather powerful.

If I were you, I would install octoprint exclusively on your Raspberry Pi 3, and then buy a Raspberry Pi 4 for the other services.

I'm running Pi-hole and a wireguard VPN on an old Raspberry Pi 2, which is perfectly fine if you are not expecting gigabit speeds on the VPN.

On a RPi 3 mod B? Not really. Load spikes have already been mentioned and especially Home Assistant is prone to them, PiHole can be, but it can be avoided (you still wouldn't want it to update its blocking lists while you print something as it causes load spikes).

IF you do it you need to configure it in a way that the Octopi is getting priority over everything else - which is possible with a lot of tinkering or using a VM layer like Proxmox - which is adding to the overhead again, though. This will push the 3B to its limits even more.

Personally I would advise against it heavily. If you already have a 3B, use it for the 3D Printer and buy another device for everything else (not necessarily a Pi, Arm has it's downsides - there are a lot of energy efficient x64 solutions out there these days.) And then slap Proxmox on it,run HAOS, Pihole and whatever comes your way in the future on it. (Paperless and Frigate/agentNVR seem to come along the way naturally.

I have PiHole and OpenMediaVault (with homeassistant docker, and dlna music server) running on a Pi2 2Gig. It has been totally fine