Orphan Single-Board Computers

A little side-excursion on hardware infrastructure.

pi_kube is a product of my fascination with Raspberry Pi and other single-board computers. The Raspberry Pi part is pretty much standard stuff in the IT-oriented parts of the maker universe. Other SBCs, though, are interesting both in terms of their technical capabilities and the ecosystems and communities they spawn. My home network includes two of these.

The first non-RPi hardware I acquired was a Rock PI 4B. Getting the device configured and running was a bit of a challenge; it doesn’t use either Raspberry Pi OS images or (AFAIK) standard arm64 boot images. I was only able to get it working with the purpose-built images that Radxa has on their website. Since I wanted to use it as a server rather than as a desktop or media center, I chose the Ubuntu “server” image, which as it turns out is a very minimal distribution indeed. It took quite a bit of wrangling to get it working consistently. Most of the problems I had were with the network configuration, which was in a confused state. I ended up disabling netplan and NetworkManager, and got it to work with a fixed address. I had high hopes of using the Rock PI as a NAS for the kubernetes cluster, but that’s a still-evolving project. Sourcing add-on boards and components for the board means ordering them from China, and with the current trade and travel restrictions and lockdowns due to the pandemic, I’m still about 35 days out from receiving what’s needed to attach an NVME SSD to the system. So more will come on this one.

My second foray into the SBC wilderness was to acquire an Atomic PI board. This is a full Intel CPU system, so it works with any amd64 OS you can get onto it. I’ve had less time to play with it, but it seems like a fairly capable system. It will handle the USB-Sata case from Amazon Basics that my RPi systems can’t drive (due to power limits, I suspect). With only a single USB port, getting it wired up to everything you want might be a challenge; fortunately, that’s an easy-to-solve issue. I was able to get the standard Ubuntu 19.10 distribution images to boot off an SSD, and then installed the server onto a USB drive. The BIOS on this system can be a little confusing, and I wasn’t able to install anything to the EMMC onboard, but I’ve got a functional mini-server running on it. I’m not quite sure what I’ll do with this system, but it’s fanless and thus quiet; it might make a good media center, or perhaps a backup for Kepler, my main development system, which runs Ubuntu 19 on an old Mac Mini that’s been tricked out with extra RAM and an SSD. The Atomic Pi has 2gb onboard, so it might not be the best desktop system, but it seems fast enough as a server.

Refactoring update

This is going to be kind of a rambling post. Sorry in advance.

I’ve done some reworking of both the hardware and software. These are presented in no particular order.

My original stack had a 1tb external HD wired up via a SATA2-to-USB3 connector which has proved problematic; I was connecting it to the master node, but I had persistent low voltage warnings. I’ve got some plans to run the HD off a powered USB hub, but with COVID-19 messing with everyone’s work and shipment schedule, it might be a month before the parts required arrive. So in the meantime, I’ve replaced the drive with a USB flash drive. This is only a 16gb drive, but it’s enough to let me tinker with NFS and persistent volumes.

With that settled, I’ve done some ansible work to get an NFS server configured on the master node, and have NFS clients running on each of the worker nodes. This lets me have a common pool for persistent volume claims to work off. I haven’t actually started using PVCs yet, so no idea how well this will work, but it’s a start.

I’ve added a Rock Pi 4 from Radxa to the stack. Eventually, once the power issues are resolved, my plan is to convert this to a dedicated NAS (perhaps using Open Media Vault) and take the NFS server burden off the master node. The Rock Pi might be a challenge, as support for it seems spotty and it seems to run off images specifically created for it; we will see how this experiment works out. If all else fails, I’ve managed to pick up an Atomic Pi that might serve nicely.

I’ve replaced the BrambleCase with a Cloudlet Cluster case, also from C4Labs. I like the BrambleCase a lot, but the Cloutlet case offers easier access to the boards installed in it, which works better at this phase of the project. I’d still recommend, guardedly, the BrambleCase; it’s a fine piece of engineering, albeit a bit tough to assemble (especially with my near-60 eyes and fingers.) I’ve kept the Bramble for some other RPi projects I’m planning.

After struggling with internal name resolution issues, I’ve made two sweeping changes. First, I’ve added a dedicated RPi 4 running pihole. My main reason for doing this is because I’ve got a DNS spoofing requirement, which I’ll cover below. The second change was to systematically disable systemd-resolved on all the Ubuntu 19 systems I’m running (which includes Kepler, my day-to-day Linux desktop, which is built off an old Mac Mini, and which probably deserves a whole series of posts itself.) I have had nothing but grief and misfortune with systemd-resolved, and it’s bad enough that I’ve decided to disable it anywhere I can. There are a lot of critiques and defenses of systemd and related project out on the web; I won’t go into the controversies, because I’m not firmly in either the pro- or anti- camps as far as systemd goes, but systemd-resolved violates the principle of least surprise, and the way it works both obscures DNS resolution and intentionally breaks how classic resolv.conf/glibc resolver works. Systemd-resolved expects a world where there is one contiguous DNS namespace, and all DNS servers agree on all hosts. That doesn’t work for internal networks, which is basically every corporate network and a lot of home networks as well.

I’ve been trying to follow the series that Lee Carpenter has been doing on his RPi/k3s cluster, but I am hung up on getting cert-manager to work. I’ll update more on those issues in another post once I land on a solution, but the gist of things is: the external interface of my router is not reachable from my internal net. As a result of this, cert-manager fails its self-check, because the self-check tries to make sure that the ACME challenge url is reachable (from its container) before it actually forwards the request to letsencrypt. This doesn’t work with “regular” DNS for me, because the internet DNS resolves project.kube.thejimnicholson.com to my external IP, and the container (inside my network) can’t reach that IP. To try and solve this, I use dnsmasq internally (via pihole.) So far, this hasn’t helped, which I’ve tracked down to one of two things: either coreDNS is configured wrong in my cluster, or the cert-manager containers are hard-wired to use some external DNS rather than refer back to the node’s DNS configuration for resolving names. I’ll have more to say about this once I’ve solved it.

Installing vcgencmd on Ubuntu 19.10

  • Add the ppa for it: sudo add-apt-repository ppa:ubuntu-raspi2/ppa
  • Edit /etc/apt/sources.list.d/ubuntu-raspi2-ubuntu-ppa-eoan.list. Change eoan to bionic, because bionic is the latest supported release.
  • Do sudo apt update
  • Do sudo apt install libraspberrypi-bin

This will install vcgencmd.

This can be easily automated using ansible:

  - name: Set up the ppa for vcgencmd
    become: true
        repo: ppa:ubuntu-raspi2/ppa
        codename: bionic

  - name: Install ubuntu raspberry pi support library
        name: libraspberrypi-bin

Taken from here.

Preparing the system OS image

Download the Ubuntu raspberry pi image from the Ubuntu Server for Raspberry Pi page.

Then use the gnome-disks program to copy it onto an SD card.

And then wait.

Once the image has been written, remove the SD card and then reinsert it (if necessary; about half the time it just mounted the new partitions for me.) Then you need to do things:

  1. Create an empty file called “ssh” on the system-boot partition. There are any number of ways to do this, but something like touch /media/$USER/system-boot/ssh should work if you like working from the command line.
  2. There will be a file in the system-boot partition named nobtcmd.txt. This file contains the kernel command line options used when linux is started. To work with k3s, you want to add cgroup_memory=1 cgroup_enable=memory to the end of the line.
  3. If you want to overclock your Pi, you should add your overclock parameters to usrcfg.txt in the system-boot partition. This is slightly different from the way you do it in Raspbian, where you edit config.txt directly; The Ubuntu boot system has things broken out a bit more.

You need to do these things for each SD card you’re setting up. Once this is done, you will have a system image that will boot Ubuntu on your cards, and you’re ready to start deploying things.

Hardware Choices

The hardware I used to create the cluster consists of:

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