gpk blog

Resetting an Ideal Halo Zigbee Thermostat

Thu, 27 Nov 2025 20:59:00 +0000

I recently bought a house with an Ideal boiler and a wireless thermostat called a “Halo”. The boiler has a “Halo Smart Interface” fitted into it, which should tell the boiler when to fire. The Halo itself contains the thermostat and communicates with the Smart Interface using Zigbee.

During some decorating work the thermostat became disconnected from the boiler. This really confused the boiler, causing it to remain on, burning gas, indefinitely. This is quite concerning and doesn’t give me much faith in the system, but that’s a future problem. Right now I just need it to work.

My Homelab

Sun, 26 Oct 2025 22:25:00 +0000

It’s been about eight years since I started running network services in my home. It all started with Pi-hole, which I ran not on a Raspberry Pi, but an Atom-powered Dell Mini “thin client” I acquired from eBay. Today I run a lot more and it’s become what is now known as a Homelab.

I’m quite fond of it all, so thought I might as well write about it.

NAS

I built my NAS around five years ago. At the time my PC was in a Fractal Design Node 804 case, but I decided this was much more suitable for use as a NAS, so I transplanted my PC into a smaller case and used the Node for my NAS. The specs are as follows:

Run AI Agents in Lightweight Sandboxes

Sun, 31 Aug 2025 12:18:00 +0000

Currently, “AI agents” like Claude Code are all the rage for software development. These programs facilitate feeding context into LLMs directly from your codebase and environment by empowering the LLM to read/write files and run arbitrary code on your system.

If you’re at all security conscious, the above should make you very uncomfortable. An intentionally non-deterministic model running arbitrary code and reading arbitrary files? No thanks. What’s worse is programs like Claude Code are not even open source. As a rule I go to lengths to avoid proprietary software, but I decided to cave on Claude Code just to see what all the fuss is about.

Think Twice about Boolean Fields in your Data Model

Sun, 31 Aug 2025 11:50:00 +0000

The SQL standard includes a boolean type which, unsurprisingly, represents a Boolean value. This can be useful, but I’m going to argue that it should almost never be used in a normalised data model.

The Problems with Boolean

Here are few of the problems you’ll inevitably run into if you use boolean in a normalised data model:

It’s not really binary

So you’re chatting to your domain expert and he says something like “books are either hardback or paperback”. Something twigs in your mind: two options… binary… that’s a Boolean! So you duly write:

Just Send Me the Prompt

Thu, 31 Jul 2025 09:41:00 +0000

If you are thinking about using an LLM to communicate with me, you will be glad to hear I’ve just developed an exciting new technique which will save us both time. Rarely are such wins possible, so this is surely cause for a celebration.

The technique goes as follows:

Type up your LLM prompt,
(Here’s where it gets really exciting), instead of sending your prompt to an LLM, just send the prompt directly to me!

“What?” I hear you crying, “My prompt doesn’t contain all the information you need!”

Automating Metabase Upgrades on Kubernetes with Flux

Tue, 27 May 2025 21:04:00 +0000

Metabase is a really nice free software business intelligence tool. It’s quite easy to deploy; they provide a Docker image and all you really need for a production instance is your own database.

I use Flux to manage my cluster so I thought it would be nice to utilise image update automation to keep up to date with updates automatically. But Metabase makes this slightly difficult because it doesn’t use proper semantic versioning on the image tags.

Clean Domain Models with SQLAlchemy

Sun, 08 Dec 2024 21:42:00 +0000

One of the most tried and tested techniques in programming is to build components that map closely to the real-world problems you are trying to solve. In domain-driven design (DDD), one of the key tenets is to have a domain model at the centre of your application.

The domain model should be built in close collaboration with domain experts and, crucially, should consist purely of high-level domain logic and be completely free of low-level application logic like databases, GUIs, web frameworks etc.

Talos Linux on XCP-ng

Sat, 09 Nov 2024 16:19:00 +0000

Talos Linux is a minimal Linux distribution designed purely for running Kubernetes nodes. It’s pretty neat, check out its website here: https://www.talos.dev/

I use XCP-ng in my homelab for running virtual machines and decided to set up a Talos cluster there. I followed the excellent Getting Started guide but there are a few additional things I wanted to do right from the start:

Have the Xen Guest Tools (aka Xen Guest Utilities, xe-guest-utilities. xen-guest-agent etc.) installed on the nodes,
Have static IP addresses.

I also had to configure the installation disk as mentioned in the guide, to /dev/xvda.

Hillshading on my Static Maps

Tue, 15 Oct 2024 21:43:00 +0000

In a previous article I wrote about adding maps to my blog, which is a static site. I use these maps to write about walks I’ve done. These maps can be dragged, rotated and zoomed, but there is no backend tileserver supporting it, it all comes from a single static file. This is thanks to the PMTiles format and support by the frontend renderer maplibre-gl.

In the original article I took a pre-made pmtile file of the world from the Protomaps project and extracted a smaller part using the pmtiles CLI. Later I ended up making my own pmtiles directly from OpenStreetMap data, which I’ll describe below. This provides a lot of geographic data like coastlines, forests, roads etc., but what I really wanted was hillshading, which I’ve now figured out.

West Highland Way

Thu, 10 Oct 2024 22:33:00 +0000

The West Highland Way is a waymarked, long-distance path in Scotland. It starts just north of Glasgow and ends at Fort William in the Highlands. It is probably the most famous of Scotland’s Great Trails (similar to the National Trails in England and Wales). In September 2024 I walked the West Highland Way over seven days with my partner Vicki.

Planning

At 154 km the WHW will take most people between 5-10 days to complete. We didn’t fancy any super long days, so we decided to do it in 7 days.

Kubernetes Ingress vs Load Balancer

Tue, 06 Aug 2024 21:10:00 +0000

I’ve been using Kubernetes successfully for a while, but I felt like I still didn’t fully understand the difference between an Ingress and a LoadBalancer. Whenever I tried to find an explanation I’d find some vague thing like “they are sort of the same, but not really”.

The problem is I was thinking about these things wrong. One is not a replacement for the other; they exist in different planes of abstraction within k8s. For someone who just wants to deploy a web service, there are three orthogonal concepts you need to understand in k8s.

Make Reading a Habit

Sun, 04 Aug 2024 12:18:00 +0000

Habits are really important. Long-term goals are too but, ultimately, habits are what you are doing to yourself day in, day out. Your habits determine what goes into your body (your diet), your physical condition (diet and exercise) and your mental condition (sleep and everything else).

I think you should make reading one of your habits.

The benefits of reading are many. First of all, it’s a great form of entertainment. You can read anywhere; you won’t disturb anyone. I love films, but the books are almost always better than the films. Really. A good book can conjure images in the mind that a film could never capture and these images never age. You’ll never go back to a favourite book and be disappointed at how bad the CGI looks now.

Odd Problem Accessing OPNsense Web UI via "OPT1" Interface

Wed, 24 Apr 2024 21:50:00 +0000

I ran into a weird problem where I couldn’t access the OPNsense web UI using an OPT1 interface. The fix is easy, but it can be very confusing and it’s all caused by an unintuitive default.

tl;dr

If you can’t access the web UI via an OPT1 interface, try disabling the “reply-to” feature: https://docs.opnsense.org/manual/interfaces.html

I’ve been playing around with OPNsense inside a VM as I prepare to replace my current pfSense router which is no longer fast enough. I have a quad network card which is passed through at the hardware level and, in addition, I have the virtual network interface provided by the hypervisor, xcp-ng.

Git is a Version Control System

Sat, 24 Feb 2024 17:23:00 +0000

The title of this post isn’t supposed to be provocative. After all, it’s simply the textbook definition of what git is. So why bother stating it? Well, I’ve worked with a fair few junior developers now and I’m starting to see a pattern. Many of these developers have never programmed without git and they see git simply as “the way to get new code into a repository”. A glorified copy, essentially—but an annoying one that is prone to going wrong.

Norfolk Coast Path

Thu, 15 Feb 2024 23:33:00 +0000

The Norfolk Coast Path (NCP) is a waymarked, long-distance footpath and National Trail in England. It stretches from Hunstanton all the way along the Norfolk coastline to Hopton. I walked it with my partner Vicki over the course of seven days in September 2022.

Planning

The NCP is around 135 km (83 miles) long and quite flat. The way is mostly on good, well trodden paths with some slower sections on sandy and shingle beaches (but you can often choose to walk inland on firmer ground instead). Fortunately there are no pebbles and the shingles didn’t become too tiring.

Emacs Undo Redo

Thu, 14 Dec 2023 22:18:00 +0000

At first glance, undo seems like a simple thing expected of most software these days and hardly worth writing about. Indeed, when I say Emacs has a very powerful undo system—probably more so than any other text editor—you may wonder what could make an undo system powerful. So let’s start by considering two big problems most undo systems have:

If you undo something, make some changes, then change your mind, what you undid is now lost and unrecoverable,
If you make changes in two parts of the same file you cannot undo changes in the first part without undoing changes in the second part too.

Emacs comes with solutions to each of these out of the box. Read on to understand how it works and how we can improve upon the defaults even more.

Bash History Hacks

Tue, 05 Dec 2023 22:22:00 +0000

When you work a lot on the command line, history can be invaluable. I’ve lost count of the number of times I’ve forgotten how I ran some earlier command and used my bash history to find out what it was. This is one of the big advantages of using CLIs over GUIs.

Accessing history

The main interface I use to my history is ^P (Ctrl-P). This recalls the previous command from history. Subsequent presses step further back and ^N steps forward again. These keys are set in muscle memory at this point, I use them that much (they also work in emacs and many other places).

A Lament for the Firefox Quick Find Key

Thu, 16 Nov 2023 20:14:00 +0000

For as long as I’ve been a Firefox user—almost 20 years at this point—it has featured a “quick find” bound to the venerable / (forward slash) key.

Following a pattern established by other software like less, man, and vi the slash key was simple: it finds stuff in the current page.

Common patterns like this are great. It’s why everyone has agreed on what Ctrl-C and Ctrl-V (or very similar) should do across all operating systems. The / key used to be like this, but not any more.

Using Nerd Icons in Org Agenda

Tue, 14 Nov 2023 23:56:00 +0000

Org mode supports icons in its agenda views. The icons can be given as either file paths to images (like SVGs), as image data or as a display property. I use a Nerd Font along with the nerd-icons package in my Emacs config, so I thought I might as well enable icons in my org agenda views.

The nice thing about using nerd fonts is this works perfectly in text mode too (assuming you have a nerd font configured for your terminal emulator).

Custom Static Vector Maps on your Hugo Static Site

Fri, 27 Oct 2023 00:11:00 +0000

This blog is a static site built with Hugo. Being static means it can be served from a basic, standard (you might say stupid) web server with no server-side scripting at all. In fact, this blog is currently hosted on Github Pages, but it could be anywhere.

Up until now, if you wanted to include an interactive map on a static site you were limited to using an external service like Google Maps or Mapbox and embedding their JS into your page. This would then call to their non-static backend service to produce some kind of tiles for your frontend.

Working on Multiple Web Projects with Docker Compose and Traefik

Mon, 02 Oct 2023 09:00:00 +0000

Docker Compose is a brilliant tool for bringing up local development environments for web projects. But working with multiple projects can be a pain due to clashes. For example, all projects want to listen to port 80 (or perhaps one of the super common higher ones like 8000 etc.). This forces developers to only bring one project up at a time, or hack the compose files to change the port numbers.

Resolving Private IP Addresses with pfSense DNS Resolver

Sun, 01 Oct 2023 23:10:00 +0000

I use the Unbound DNS resolver built in to pfSense. By default the resolver filters out any results that are private IP addresses. Normally this makes sense: no public domain should have a private address. But sometimes it does make sense. For example there are some useful services like sslip.io that will resolve to any IP address that you like. So 127.0.0.1.sslip.io resolves to to 127.0.0.1. This is can be useful for local development, especially when working with containers and reverse proxies and the like.

Why is Emacs Hanging?

Thu, 21 Sep 2023 14:10:00 +0000

Even after using Emacs for 15 years there’s still so much I can learn. I probably should have already known this, but there’s a first time for everything.

It’s rare that Emacs hangs. Exceedingly rare. Which is probably why I didn’t know how to deal with it. Today Emacs started hanging when trying to open files over a remote TRAMP session (SSH).

The most important key of all that everyone who uses Emacs knows is C-g. This is the universal “quit” key and it has the power to interrupt any long running processes. What I didn’t know about is M-x toggle-debug-on-quit. I’ve used toggle-debug-on-error extensively when programming Elisp (I even have it bound to a key in Elisp buffers). toggle-debug-on-quit is similar except the debugger is invoked when you C-g.

Replacing Strings in an Entire Project

Tue, 22 Aug 2023 14:22:00 +0000

This is a little trick I just applied and thought was cool enough to write down.

Let’s say you want to replace a name that is used throughout a project. Due to various conventions/restrictions in use the name might appear in several forms like: MY_COOL_NAME, my-cool-name, my_cool_name etc.

In Emacs you can invoke regexp replace across an entire project by invoking project-query-replace-regexp, by default bound to C-x p r. This will first prompt for the regexp to search for, then what to replace it with.

My 2023 Emacs Python Setup

Tue, 15 Aug 2023 14:19:00 +0000

I’ve been using Emacs for almost 15 years now. Somewhat surprisingly, I hadn’t touched my config in three years! It’s been working that well. But now that Emacs 29 has been released I’ve decided to take a look at what’s new and there have been some big changes, particularly for Python.

Goodbye Elpy, Goodbye Projectile

Elpy has been the primary mode for Python development for me for years now. But sadly, it looks like the project is no more. The good news is there are better ways to do what it did. It’s bittersweet to say goodbye to it and I will be eternally grateful to the authors, but progress is progress.

Install Calibre without Root

Sun, 13 Aug 2023 13:23:00 +0000

On Linux, software should generally be installed with your system package manager (apt, yum, portage etc.) However, Calibre is a bit “special” in this respect. While well-loved, it’s known to be a bit difficult to package (to say the least) and most distro packages you’ll find are out of date. The official website recommends against using any distro packages and instead installing it directly from the site.

Unfortunately, the official instructions are problematic for a number of reasons. For a start, copying and pasting commands from the browser is considered dangerous. But that’s easy to fix, in bash do Ctrl-X Ctrl-E and your preferred text editor will be opened for you to type your command. This means you can inspect what is pasted before is run (save the file then exit the editor to run the command). Very important. Always do this when copy/pasting from the web.

Cooking with Make

Thu, 03 Aug 2023 00:00:00 +0000

In which I compare cooking food with building software

Arduino Programming with Emacs

Mon, 31 Jul 2023 19:30:00 +0000

If you want to start Arduino programming you’ll notice a lot of the documentation and tutorials are centred around the Arduino IDE. Now, obviously, as an Emacs user you’ll be loath to install something like Arduino IDE, let alone actually use it. The good news is it’s super easy to get started with Arduino with any editor, including Emacs and even Vim if you so desire.

All the Arduino IDE is doing is calling a cross-compiler toolchain then using avrdude to communicate with the Arduino to upload software. The Arduino Uno and Nano both use the Atmel AVR platform so what you need is a toolchain that can target that platform. Now, you could install your own toolchain and call avrdude directly. If you know how to do that then I guess you can stop reading now. But if you don’t, or aren’t interested in learning how (it’s not very interesting), then read on.

Building a Home Cinema on a Shoestring

Mon, 24 Jul 2023 14:25:00 +0000

I love going to the cinema, but I’ve always been disappointed that I can’t see older films and I can’t see them when it’s convenient for me. There have always been ways to watch films at home, but even today when large screens and high-definition formats are ubiquitous, it’s just not the same as the cinema experience. There’s something completely different about the big screen that a TV in a living room can’t replicate. For that reason I’ve wanted my own home cinema for as long as I can remember. The problem is I don’t want to spend a lot of money on it.

Writing a Blog with Org-mode

Sat, 15 Jul 2023 13:43:00 +0000

I’ve always thought I should write a blog, but I just never got around to setting it up. I know there are services you can simply sign up to and start writing, but that isn’t for me. I have two requirements for this thing:

I can write using tools of my choice,
I can host it anywhere.

My tool of choice for writing anything is emacs and, for natural language in particular, org-mode. This is a bit like markdown, but better. For version control and deployment I use git.