These are my notes as I am working my way through this book from PragProg. I am reading a beta version of the book so things may change. I’ll be posting this to my github repo: (https://github.com/chriseyre2000/designing_elixir)

The introduction starts by building a simple counter application as the domain and wraps it in a send/receive process with an API.

The code samples here are clean and clearly ordered. The only note that I have found so far is that I needed to delete the autogenerated Count.ex file to avoid a warning.

Takeaway from the intro: Supervisors are about lifecycles.

Takeaway from type introductions: Send the functions to the data!

Chapter 3 typo: response.ex is misspelt (reported).

excoveralls looks to be a better code coverage tool.

I spent some of today trying to work out why a Docker image that I was using did not work correctly.

This is the most useful command for debugging a docker image:

docker run -it ubuntu /bin/bash

This is based upon the ubuntu image but feel free to replace it with whatever you are trying to debug.

You can do the same with a docker-compose

docker-compose run --entrypoint /bin/bash

I am now looking at how to run a gradle build inside a docker container and then extract the log files. It will be especially useful to be able to view the log files. It may be possible to add a web server to view them.

It’s now also possible to stand up a Jenkins server on your dev machine to test Jenkinsfiles before deploying them to the build server.

docker run -p 8080:8080 -p 50000:50000 jenkins/jenkins:lts

Chapter 4

I am still working my way through this book.

The main difficulty that I am finding with chapter 4 is the scattered nature of the example code. It’s all small snippets, some of which references code in the previous chapter.

This is in addition to the Erlang => Elixir translations:

• atom => :atom
• VariableName => variable_name
• moduleName => ModuleName

Some of the Elixir functions are reordered for consistency.

#Erlang
1> gen_server:start_link({local, timeout}, timeout, [], []).

#Elixir
1> c "Timeout.ex"
2> GenServer.start_link(Timeout, [], name: :timeout)
3> GenServer.call(:timeout, {:sleep, 100})
4> GenServer.call(:timeout, {:sleep, 5001})

The GenServer will by default timeout if a message takes more than 5 seconds to respond.

Samples for Chapter 4 have been pushed to

https://github.com:chriseyre2000/scalability_ex with hash: cc8dd44

Chapter 5

The Erlang sys module can be reference from iex using :sys

The the log commands require atoms.

:sys.log(Frequency, :print)

:sys.log(Frequency, :get)

Now at hash: 830c1ea

Chapter 6

This is an odd chapter for Elixir as the Finite State Machine was considered defective and was not adapted as a wrapper. I am going to skip this chapter

Chapter 7

GenEvent has also been Deprecated

This is another of my book walk through series. This time I am working on Designing for Scalability with Erlang/OTP.

This is the book that goes into detail about OTP in general.

Chapter 2 : Introducing Erlang

https://github.com/chriseyre2000/scalability_ex (edc0862)

The above is a repo with commit hash of where I have currently got to.

So far we have some basic recursion and some manual send/receive logic.

We have now seen the first use of ets – Erlang Term Storage a simple persistence layer.

You build it you support it (even if not first line). It’s the other side of continuous delivery. You also need the right to fix anything that could wake you up. It focuses the developers minds to proper testing, logging, auditing and error handling. There is no wall.

Management frequently believes that the value of the advice is proportional to the cost. Also, knowledge gained outside an organisation is more valuable than that gained within.

I have been encouraging my team to automate everything.

To live by this principle I have started to automate my bank spreadsheet. I keep a spreadsheet with all of my banking transactions. This comes in handy should I need to investigate an old transaction. My current sheet covers the last 9 years. I had been manually copying the details over.

My bank allows statements to be exported as CSV files.

Here is a simple bash script that allows the data to be put into the format that I want:

cat filename.csv | awk -F, ‘{print $1 “,” $5 “,” $7 “,” $6 }’ | sed ‘1d’ | tail -r

I like the newest transactions at the bottom and credits before debits.

This becomes much easier to import into a google sheet rather than fighting with open office.

I have multiple current accounts and rebalance the main current account to a fixed amount at the end of each month. The remainder is moved into an offset mortgage. Credit card bills get paid (when due) from the mortgage account. This maximised the offset benefit.

Commands are sent to dependabot by commenting on a pull request.

@dependabot ignore this major version

This command will prevent dependabot from suggesting any further upgrade to a given dependency until it has been manually advanced past a certain point. This is really useful if you want to keep your node to a LTS version and don’t want to keep getting notified of bleeding edge changes.