Continuous Delivery

Is an excellent book by Jez Humble and Dave Farley. As usual I'm going to quote from a few pages...
Software delivers no value until it is in the hands of its users.
The pattern that is central to this book is the deployment pipeline.
It should not be possible to make manual changes to testing, staging, and production environments.
If releases are frequent, the delta between releases will be small. This significantly reduces the risk associated with releasing and makes it much easier to to roll back.
Branching should, in most circumstances, be avoided.
Dashboards should be ubiquitous, and certainly at least one should be present in each team room.
One of the key principles of the deployment pipeline is that it is a pull system.
A corollary of having every version of every file in version control is that it allows you to be aggressive about deleting things that you don't think you need... The ability to weed out old ideas and implementations frees the team to try new things and to improve the code.
It should always be cheaper to create a new environment than to repair an old one.
The goal of continuous integration is that the software is in a working state all the time... Continuous is a practice not a tool... Continuously is more often than you think.
The most important practice for continuous integration to work properly is frequent check-ins to trunk or mainline.
Ideally, the compile and test process that you run prior to check-in and on your CI server should take no more than a few minutes. We think that ten minutes is about the limit, five minutes is better, and about 90 seconds is ideal.
Enabling developers to run smoke tests against a working system on a developer machine prior to each check-in can make a huge difference to the quality of your application.
Build breakages are a normal and expected part of the process. Our aim is to find errors and eliminate them as quickly as possible, without expecting perfection and zero errors.
Having a comprehensive test suite is essential to continuous integration.
You should also consider refactoring as a cornerstone of effective software development.


Building Microservices

Is an excellent book by Sam Newman. As usual I'm going to quote from a few pages...
Because microservices are primarily modeled around business domains, they avoid the problems of traditional tiered architectures.
Microservices should cleanly align to bounded contexts.
Another reason to prefer the nested approach could be to chunk up your architecture to simplify testing.
With an event-based collaboration, we invert things. Instead of a client initiating requests asking for things to be done, it instead says this thing happened and expects other parties to know what to do. We never tell anyone else what to do.
We always want to maintain the ability to release microservices independenty of each other.
A red build means the last change possibly did not intergrate. You need to stop all further check-ins that aren't involved in fixing the build to get it passing again.
The approach I prefer is to have a single CI build per microservice, to allow us to quickly make and validate a change prior to deployment into production.
No changes are ever made to a running server.
Rather than using a package manager like debs or RPMs, all software is installed as independent Docker apps, each running in its own container.
Flaky tests are the enemy. When they fail, they don't tell us much... A test suite with flaky tests can become a victim of what Diane Vaughan calls the normalization of deviance - the idea that over time we can become so accustomed to things being wrong that we start to accept them as being normal and not a problem.
All too often, the approach of accepting multiple services being deployed together drifts into a situation where services become coupled.
Most organizations that I see spending time creating functional test suites often expend little or no effort at all on better monitoring or recovering from failure.


Developer on Fire

Recently I was honoured to be interviewed by Dave Rael, the man behind Developer on Fire.
Click the image below to listen :-)


the design and evolution of cyber-dojo

I've talked about the design and evolution of cyber-dojo at two conferences this year. First at NorDevCon in Norwich and then also at Agile on the Beach in Falmouth. Here's the slides.



cyber-dojo traffic-lights

My friend Byran who works at the awesome Bluefruit Software in Redruth has hooked up his cyber-dojo web server to an actual traffic-light! Fantastic. Check out the video below :-)



Byran writes
It started out as a joke between myself and Josh (one of the testers at Bluefruit). I had the traffic lights in my office as I was preparing a stand to promote the outreach events (Summer Huddle, Mission to Mars, etc...) Software Cornwall runs. The conversation went on to alternative uses for the traffic lights, I was planning to see if people would pay attention to the traffic lights if I put them in a corridor at the event; we then came up with the idea that we could use them to indicate TDD test status.
Although it started out as a joke I am going to use it at the Summer Huddle, the lights change every time anyone runs a test so it should give an idea of how the entire group are doing without highlighting an individual pair.
The software setup is very simple, there is a Python web server (using the Flask library) running on a Raspberry Pi that controls the traffic lights using GPIO Zero. When the appendTestTrafficLight() function (in run_tests.js.erb) appends the traffic light image to the webpage I made it send an http 'get' request to the Raspberry Pi web server to set the physical traffic lights at the same time. At the moment the IP address of the Raspberry Pi is hard coded in the 'run_tests.js.erb' file so I have to rebuild the web image if anything changes but it was only meant to be a joke/proof of concept. The code is on a branch called traffic_lights on my fork of the cyber-dojo web repository.
The hardware is also relatively simple, there is a converter board on the Pi; this only converts the IO pin output connector of the Raspberry Pi to the cable that attaches to the traffic lights.
The other end of the cable from the converter board attaches to the board in the top left of the inside the traffic lights; this has some optoisolators that drive the relays in the top right which in turn switch on and off the transformers (the red thing in the bottom left) that drive the lights.
I have to give credit to Steve Amor for building the hardware for the traffic lights. They are usually used during events we run to teach coding to children (and sometimes adults). The converter board has LEDs, switches and buzzers on it to show that there isn't a difference between writing software to toggle LEDs vs driving actual real world systems, it's just what's attached to the pin. Having something where they can run the same code to drive LEDs and drive real traffic lights helps to emphasise this point.


cyber-dojo update

Between my recent fishing trips I have been working hard on a new cyber-dojo architecture.
  • pluggable default start-points so you can now use your own language/tests and exercises lists on the setup page
  • a new setup page for your own pluggable custom start-points
  • once I've got the output parse functions inside the start-point volumes I'll be switching the public cyber-dojo server to the new image and updating the running-your-own-server instructions
  • I've switched all development to a new github repo which has instructions if you want to try it now.


River Tone chub/roach

Last week I broke my Daiwa Spectron spliced-tip rod which has served me for 25 years+. After some searching around I replaced it with a Drennan Acolyte Ultra 14ft. I christened it yesterday with my heaviest ever bag on the Tone; 80lb+ of chub and roach with a few skimmer bream, one roach-bream hybrid, and several small perch. All caught on waggler, red/yellow/white maggot, on 1.7lb hooklength, and a size 20 Kamasan B560. Wooohooo.



Verdal salmon

Once a year a spent a glorious week fishing for salmon on the River Verdal in Norway. This year, despite the low water, I caught this cracker. A huge thanks to John Oldren who owns the beat. You will not find a more hospitable host. Also to Gary Scott for being super helpful as always.



Tulchan salmon

One of my favourite salmon beats is Tulchan on the river Spey.
On my most recent trip I caught two, including this beauty from Hunter's Pool.