Experimenting With Elixir in Docker

I am working on my book Elixir Function Guide. Having noticed that there are a lot of mix tasks that I did not know about (and some that my exercism.io students don’t) then I thought that I would add some details at the start of the book.

I started using mix help to list the available functions:

mix                   # Runs the default task (current: "mix run")
mix app.start         # Starts all registered apps
mix app.tree          # Prints the application tree
mix archive           # Lists installed archives
mix archive.build     # Archives this project into a .ez file
mix archive.install   # Installs an archive locally
mix archive.uninstall # Uninstalls archives
mix clean             # Deletes generated application files
mix cmd               # Executes the given command
mix compile           # Compiles source files
mix credo             # Run code analysis (use `--help` for options)
mix credo.gen.check   # Generate a new custom check for Credo
mix credo.gen.config  # Generate a new config for Credo
mix deps              # Lists dependencies and their status
mix deps.clean        # Deletes the given dependencies' files
mix deps.compile      # Compiles dependencies
mix deps.get          # Gets all out of date dependencies
mix deps.tree         # Prints the dependency tree
mix deps.unlock       # Unlocks the given dependencies
mix deps.update       # Updates the given dependencies
mix do                # Executes the tasks separated by comma
mix escript           # Lists installed escripts
mix escript.build     # Builds an escript for the project
mix escript.install   # Installs an escript locally
mix escript.uninstall # Uninstalls escripts
mix format            # Formats the given files/patterns
mix help              # Prints help information for tasks
mix hex               # Prints Hex help information
mix hex.audit         # Shows retired Hex deps for the current project
mix hex.build         # Builds a new package version locally
mix hex.config        # Reads, updates or deletes local Hex config
mix hex.docs          # Fetches or opens documentation of a package
mix hex.info          # Prints Hex information
mix hex.organization  # Manages Hex.pm organizations
mix hex.outdated      # Shows outdated Hex deps for the current project
mix hex.owner         # Manages Hex package ownership
mix hex.publish       # Publishes a new package version
mix hex.repo          # Manages Hex repositories
mix hex.retire        # Retires a package version
mix hex.search        # Searches for package names
mix hex.user          # Manages your Hex user account
mix loadconfig        # Loads and persists the given configuration
mix local             # Lists local tasks
mix local.hex         # Installs Hex locally
mix local.phx         # Updates the Phoenix project generator locally
mix local.public_keys # Manages public keys
mix local.rebar       # Installs Rebar locally
mix new               # Creates a new Elixir project
mix phx.new           # Creates a new Phoenix v1.4.0 application
mix phx.new.ecto      # Creates a new Ecto project within an umbrella project
mix phx.new.web       # Creates a new Phoenix web project within an umbrella project
mix profile.cprof     # Profiles the given file or expression with cprof
mix profile.eprof     # Profiles the given file or expression with eprof
mix profile.fprof     # Profiles the given file or expression with fprof
mix release           # Assembles a self-contained release
mix release.init      # Generates sample files for releases
mix run               # Starts and runs the current application
mix test              # Runs a project's tests
mix xref              # Prints cross reference information
iex -S mix            # Starts IEx and runs the default task

It was only then that I realised that I have a number of mix extensions installed.

I need to start with what comes out of the box.
At this point I have three choices:

  • Uninstall the extensions (these are usefull .)
  • Manually edit out the extensions (error prone)
  • Use docker

The docker option is appealing as it will allow me to test using different versions of Elixir.

Here is the simple option that allows the use of docker:

docker run -it elixir:1.10 /bin/bash

This downloads the image and runs up the container. Note that this starts with bash, rather than the default iex.

From this mix help gives the more useful list:

mix                   # Runs the default task (current: "mix run")
mix app.start         # Starts all registered apps
mix app.tree          # Prints the application tree
mix archive           # Lists installed archives
mix archive.build     # Archives this project into a .ez file
mix archive.install   # Installs an archive locally
mix archive.uninstall # Uninstalls archives
mix clean             # Deletes generated application files
mix cmd               # Executes the given command
mix compile           # Compiles source files
mix deps              # Lists dependencies and their status
mix deps.clean        # Deletes the given dependencies' files
mix deps.compile      # Compiles dependencies
mix deps.get          # Gets all out of date dependencies
mix deps.tree         # Prints the dependency tree
mix deps.unlock       # Unlocks the given dependencies
mix deps.update       # Updates the given dependencies
mix do                # Executes the tasks separated by comma
mix escript           # Lists installed escripts
mix escript.build     # Builds an escript for the project
mix escript.install   # Installs an escript locally
mix escript.uninstall # Uninstalls escripts
mix format            # Formats the given files/patterns
mix help              # Prints help information for tasks
mix loadconfig        # Loads and persists the given configuration
mix local             # Lists local tasks
mix local.hex         # Installs Hex locally
mix local.public_keys # Manages public keys
mix local.rebar       # Installs Rebar locally
mix new               # Creates a new Elixir project
mix profile.cprof     # Profiles the given file or expression with cprof
mix profile.eprof     # Profiles the given file or expression with eprof
mix profile.fprof     # Profiles the given file or expression with fprof
mix release           # Assembles a self-contained release
mix release.init      # Generates sample files for releases
mix run               # Starts and runs the current application
mix test              # Runs a project's tests
mix xref              # Prints cross reference information
iex -S mix            # Starts IEx and runs the default task

Installing Lumen

Lumen is an alternative BEAM Implementation.
Warning that this is still at a very early stage. It promises the ability to build WebAssembly

I am not currently interested in using Rust to build it from sources, but there are now images published here

https://github.com/lumen/lumen/releases

I used the following to install the tarball (I use a mac):

sudo tar xf lumen-0.1.0-nightly-x86_64-apple-darwin.tar.gz -C /opt

This deploys the bundle to: /opt/lumen

The compiler is now available at: /opt/lumen/bin/lumen

Here are more details on lumen: https://getlumen.org/

On having a Useless Superpower

I am going to admit to having a minor superpower. I can hear high pitch sounds that most people can’t.

This is not at all useful as it results in me getting a headache in lots of shops or museums (and in one especially annoying instance a job interview). It’s typically a 50hz signal.

Minimalist Clustering Demo

This is based on code from a video that I have previously linked to.
However Elixir has made a few breaking changes since then.

This is going to demonstrate how to cluster two local Elixir nodes, deploy code from one to the other and then upgrade it while it is running.

You need to put the following code in a file called blabber.ex

defmodule Blabber do

  def start do

    spawn(fn -> loop(0) end)

  end

  def loop(uptime) do

    receive do

      :stop ->

        IO.puts "Shutting blabber down ..."

        exit(:normal)

      after 1000 ->

        IO.puts "Nice! #{uptime} seconds of bgu-free uptime on #{node()}."

    end

    Blabber.loop(uptime + 1)

  end

end

Next you need to start iex with a name and a cookie (in the same folder as blabber.ex):

iex --sname cat --cookie super-secret

In a second terminal start another iex session

iex --sname dog --cookie super-secret

From the first terminal connect the two nodes together:

Node.connect :"dog@MacBook-Pro"

Compile the code in the cat node:

c ("blabber.ex", ".")

We need to use this version of the compile function as by default since Elixir 1.5 the beam file is not output by default.

The process can be started on the cat node with:

Blabber.start

Now you can transfer the compiled beam file to all linked nodes using:

nl Blabber

Now from the dog node you can start the process:

Blabber.start

At this point we notice the typo in the code. It say bgu-free rather than bug-free.
Edit the source file save the change.

On the cat node recompile this:

c ("blabber.ex", ".")

This will immediately fix the problem on the cat node (and leave the count updating).

If you use:

nl Blabber

then the solution will be moved to the other node as well.

This demonstrates the simplest possible Clustering arrangement. It is simple to extend this to a move sophisticated service.

Twitter For Tech Support

Sometimes a companies official Tech Support channels can be a little slow.

If the official channels don’t work then you can turn to twitter. Raising a support issue on a social media site can cause the company to take action. Sometimes a DM to them will enable action that a support ticket does not.

Frequencies

This is a simple powershell script that can be used to get the frequency of the first letter from a sample file.

gc ‘./sample’ | %{ $_.substring(0,1) } | group

Running this over say the FTSE 100 symbol list returns:

Count Name                      Group
----- ----                      -----
   10 A                         {A, A, A, A...}
   11 B                         {B, B, B, B...}
    4 C                         {C, C, C, C}
    2 D                         {D, D}
    2 E                         {E, E}
    3 F                         {F, F, F}
    3 G                         {G, G, G}
    5 H                         {H, H, H, H...}
    8 I                         {I, I, I, I...}
    3 J                         {J, J, J}
    1 K                         {K}
    4 L                         {L, L, L, L}
    4 M                         {M, M, M, M}
    3 N                         {N, N, N}
    1 O                         {O}
    6 P                         {P, P, P, P...}
    8 R                         {R, R, R, R...}
   15 S                         {S, S, S, S...}
    2 T                         {T, T}
    2 U                         {U, U}
    1 V                         {V}
    2 W                         {W, W}

This highlights that the symbols are not uniformly spread across the alphabet.

A-F has 1/3 of the market as does P-Z

I found out this once when trying to use the ticker symbol to load balance market data across 3 servers.

Check the distribution of the data before you use a simple key.

Oddly the second letter is a better key:

    6 A                         {A, A, A, A...}
    3 B                         {B, B, B}
    4 C                         {C, C, C, C}
    5 D                         {D, D, D, D...}
    3 E                         {E, E, E}
    6 G                         {G, G, G, G...}
    4 H                         {H, H, H, H}
    3 I                         {I, I, I}
    2 K                         {K, K}
    8 L                         {L, L, L, L...}
    6 M                         {M, M, M, M...}
    7 N                         {N, N, N, N...}
    2 O                         {O, O}
    4 P                         {P, P, P, P}
    8 R                         {R, R, R, R...}
    9 S                         {S, S, S, S...}
    7 T                         {T, T, T, T...}
    2 U                         {U, U}
    6 V                         {V, V, V, V...}
    2 W                         {W, W}
    2 X                         {X, X}
    1 Z                         {Z}