10 Oct 2020
Last week the UK government announced more than 12,000 cases
of COVID-19 - more than double the number from the day before. This increase was accompanied by the following
message on the Government’s Data Dashboard.
Due to a technical issue, which has now been resolved, there has been a delay in publishing a number of
COVID-19 cases to the dashboard in England. This means the total reported over the coming days will
include some additional cases from the period between 24 September and 1 October, increasing the number
of cases reported.
This turned out to be an issue with the reporting of positive tests caused by a limit in Excel. An interesting
part of the story is the way it was initially reported in the media. Their focus is on the number of the cases
reported each day, which due to the delay in processing tests is not accurate normal, but with this delay is
a pretty meaningless number. The key measure used to make important decisions is the rolling average of new
case over the last seven days, and with this number you can’t at a glance know how the average is changing.
What is particularly odd, is that it turns out that the government do publish the number of positive cases by
the date the sample was taken. It’s just that for the last few days the media narrative has been “huge number
of cases”, even though that’s largely an artefact of the old incorrect data. Sure they’re high, but they went
up a week before, not last Saturday.
Read More...
30 Sep 2020
tap, tap, tap Hello, is this thing on?
I started this blog way back in 2008 and was fairly active through to 2012. Unfortunately, apart from a period in 2017, it
has been dormant since then. Working for a hedge fund, who are notoriously secretive, and having children, who are
notoriously good at sucking up all your free time, meant that blogging really wasn’t an option. Now I work for a
more open company (Ocado Technology) and my kids are a little
older, so require a bit less time, I’m hoping to resurrect my blog.
Originally I created the blog on Wordpress.com, which worked great. It was free, reliable, and easy
to use. Unfortunately, when I started writing a new post the editor had become unusable for me. Perhaps I’m an old
fuddy-duddy, but I just want to be able to write my text, add some simple pictures, and have the editor get out of my way.
Sadly, it quickly became clear that WordPress was going to get in my way, so it was time to give the blog a new home and a
new lick of paint.
For many years I’ve had a Linode server, which I use
to host a few small websites. I’ve always been a fan of Markdown, so a static site generated by Jekyll seemed like the obvious choice.
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22 Nov 2017
Docker is a great tool for running your applications in a consistent and
repeatable environment. One issue that I’ve come across occasionally is getting data into and out of the
environment when it’s running.
In this post I want to talk about exposing ports that are published by applications running inside a
container. When you start up the container it’s pretty easy to configure the ports you want to expose using
the --publish or -p parameter. It’s followed by the internal port number, a colon, and the
external port number. For example:
docker run --publish 80:8080 myapp
This will publish port 80 from inside the container as port 8080 on the host.
This works great if you know want ports you want to expose before you run the container. Once it’s running,
if you decide you need access to a port, you can’t expose it. Unless that is, you cheat.
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15 Nov 2017
I’m currently working with some large Java monoliths which talk to each other over ActiveMQ. There are several
aspects of the architecture that I’d like to change. Certainly, new production environments (Kubernetes, etc)
mean that monoliths are not required because of the overhead of deployment, and the benefits of easier testing
and more modular architecture mean that I think the expense of migrating to smaller services will be well
worth it. With such an established code base though, the question I’m grappling with is how can we transition
to a better, more open technology stack without needing to rewrite from scratch and do a big bang deployment.
Currently I’m toying with the idea of writing an ActiveMQ to Web Sockets bridge. Web Sockets are a way of
emulating a direct TCP connection in a web browser, although a more normal use case is to send and receive a
stream of JSON encoded events. Although Web Sockets were created for use in browsers all languages have
libraries available which will allow you to connect to a server.
ActiveMQ natively supports connecting over Web Sockets, so why would I propose building a bridge application?
In our case the messages being exchanged are binary encoded, so you can’t decode them unless you’re running
Java and have the same library used to send the messages. By building an application to act as a bridge you
get much more control over the Web Socket API than if you use the native ActiveMQ implementation, so you can
tidy up the JSON representations you use and easily make any other improvements to the API that you want.
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08 Nov 2017
In a previous post
, I talked about network booting a Raspberry Pi MythTV frontend. One issue that I had to solve was how
to turn on my Onkyo surround sound speakers, but only if they are not
already turned on.
I already had an MCE remote and receiver which can both
transmit and receive, so it is perfect for controlling MythTV and switching the speakers on. There are plenty
of tutorials out there, but the basic principle is to use irrecord to record the signals from the
speaker’s remote control, so the Raspberry Pi can replay them to switch it on when the Pi starts up. In my
case, I needed two keys, the power button and VCR/DVR input button. Once you’ve recorded the right signals,
you can use irsend to repeat them.
Initially, I had it set up to always send the power button signal on boot. This had the unfortunate
side-effect of switching the speakers off if they were already on, for example, if I had been listening to
music through Sonos before deciding to watch TV.
Read More...
