Random outpourings of a software developer
Releases are the most complete deployment option for an Elixir project.
There are several ways to deploy an Elixir application:
The last of these is the most robust solution which will permit clean upgrades.
The term Application in Elixir is akin to a library in other languages.
An Elixir solution is more of a mini operating system with processes.
We have a Conservative leadership election in the wake of the EU election results.
Here are the facts:
The EU will not reopen negotiations.
Our current extension will run out at Halloween.
There are three options for parliament:
The first has been repeatedly rejected by parliament.
The third will not be able to win over the house of commons, but will be the default should nothing be agreed.
The Brexit party would like to be part of negotiations but since the EU are not interested that won’t help.
Something needs to move, and that will either take a fresh election or a referendum.
We have a weak opposition (unable to decide if it is pro or anti Brexit) and a minority government unable to act.
The Conservatives will consider a Step to the Right (timewarp anyone?) to appeal to the Brexit party voters.
The Brexit party had no manifesto so its impossible to know what form of Brexit that they want. The best guess would be the No Deal option.
The UK faces the prospect of a new Prime Minister selected from a list that is packed with entirely unsuitable candidates:
| Candidate | Reason |
| Boris Johnson | Mr Johnson is facing a private prosecution over claims he deliberately lied during the Referendum campaign. Mr Johnson is reported to have replied: “Fuck business.” |
| Michael Gove | I think the people in this country have had enough of experts. Stabbed Boris Johnson in the front during the previous leadership campaign. |
| Jeremy Hunt | Messed up security contracts at the Olympics. Hated by the NHS. Can’t remember which country his wife is from. |
| Andrea Leadsom | “Being a mother gives me an edge on May” Withdrew from ballot versus May |
| Ester McVey | Misled parliament over the new Universal Credit scheme |
| Dominic Raab | Surprised that Britain is an island |
There are other candidates (and more will appear over the next few days).
This is a general outline for using a headless CMS (such as Contentful).
There are other ways to do this but this is fast given a suitable size delta, and will recover from failure better than webhooks:
This has the headless CMS being polled by a Static Site Generator.
The Static Site Generator knows the current state of the site and only regenerates changed items. This may require it to keep a map of dependencies between nodes. Sometimes you may need to go 3 or 4 levels deep. Store the output in S3. Serve the website from S3, which allows some customisation of the data. Use a CDN to back the website to reduce load. Purge the pages of the site that have changed after they have been written.
We managed to use a single Heroku node for the SSG and another one for the webserver.
Some of my team have been impressed with Groovy’s support for closures:
Here is a simple closure:
def time(String message, Closure body) {
def start = Instant.now()
def result = body.call()
def finish = Instant.now()
Duration duration = Duration.between(start, finish)
log.info("$message took $duration")
result
}
This would allow you to go from:
def value = complexDatabaseQuery(1, 2, 3)
to
def msg = "Complex query 1, 2, 3"
def value = time(msg, {complexDatabaseQuery(1, 2, 3)})
This provides a simple decorating wrapper that records the time that the database call took without making the code less readable.
This could be made more sophisticated using:
def warnSlow(String message, def max_duration_in_seconds = 5, Closure body) {
def start = Instant.now()
def result = body.call()
def finish = Instant.now()
Duration duration = Duration.between(start, finish)
if (duration.getSeconds() > max_duration_in_seconds) {
warn “$message is slow, it took $duration which is longer than the threshold of $max_duration_in_seconds”
}
result
}
This permits simple performance checks to be added to code with minimal disruption.
This is the third part of an exploration of the Elixir base libraries
Here is an introduction to what you get out of the box with iex:
| Letter | Module | Description |
| C | Calendar | Date, time and calendar functions |
| CaseClauseError | This is a struct used for errors. | |
| Code | Utilities for managing code compilation, code evaluation, and code loading. | |
| Collectable | Protocol to traverse data structures. Used for putting data into things. | |
| CompileError | This is a struct used for errors. | |
| CondClauseError | This is a struct used for errors. |
Doing the same with :c gives the erlang modules
| Letter | Module | Description |
| c | c | Erlang compiler. |
| calendar | Date, time and calendar functions | |
| cerl | Core Erlang abstract syntax trees. | |
| cerl_clauses | Utility functions for Core Erlang case/receive clauses. | |
| cerl_inline | ??? | |
| cerl_sets | Set functions. | |
| cerl_trees | Basic functions on Core Erlang abstract syntax trees. | |
| code | Utilities for managing code compilation, code evaluation, and code loading. | |
| code_server | Process used for live code reloading | |
| compile | Erlang compiler interface | |
| core_lib | ??? | |
| core_lint | ||
| core_parse | ||
| core_pp | ||
| core_scan | ||
| counters | Library of mutable counters with no locking. |
This is the second part of an exploration of the Elixir base libraries
Here is an introduction to what you get out of the box with iex:
| Letter | Module | Description |
| B | BadArityError | This is a struct used for errors. |
| BadBooleanError | This is a struct used for errors. | |
| BadFunctionError | This is a struct used for errors. | |
| BadMapError | This is a struct used for errors. | |
| BadStructError | This is a struct used for errors. | |
| Base | Encoding and decoding functions for 16, 32, 64, hex, url | |
| Behaviour | Mechanism for handling behaviours (deprecated) | |
| Bitwise | Performs bit calculations. |
Doing the same with :b gives the erlang modules
| Letter | Module | Description |
| b | base64 | Base 64 encode and decode |
| beam_a | Used after code generation before optimisation. Normalises the code. | |
| beam_asm | Assembler for the beam | |
| beam_block | Erlang compiler | |
| beam_bs | Erlang compiler | |
| beam_bsm | Erlang compiler | |
| beam_clean | Erlang compiler | |
| beam_dead | Erlang compiler | |
| beam_dict | Erlang compiler | |
| beam_disam | Erlang compiler | |
| beam_except | Erlang compiler | |
| beam_flatten | Erlang compiler | |
| beam_jump | Erlang compiler | |
| beam_lib | Erlang compiler | |
| beam_listing | Erlang compiler | |
| beam_opcodes | Erlang compiler | |
| beam_peep | Erlang compiler | |
| beam_receive | Erlang compiler | |
| beam_record | Erlang compiler | |
| beam_reorder | Erlang compiler | |
| beam_split | Erlang compiler | |
| beam_trim | Erlang compiler | |
| beam_type | Erlang compiler | |
| beam_utils | Erlang compiler | |
| beam_validator | Erlang compiler | |
| beam_z | Erlang compiler | |
| binary | Handles binary data. This is the Erlang string type |
I recently found out how powerful the iex tool is for documentation.
This is the general form of getting detailed documentation:
This is the start of a long series about the modules that you get out of the box.
1> h Module.function_name/arity
This returns the documentation on this specific function in the specific module.
I also found that typing a capital letter and tab expands the known modules.
Here is an introduction to what you get out of the box with iex:
| Letter | Module | Description |
| A | Access | Key based access to structures. |
| Agent | Simple abstraction around state | |
| Application | Working with applications and their callbacks | |
| ArgumentError | This is a struct used for errors. | |
| ArithmeticError | This is a struct used for errors. | |
| Atom | Convenience functions for working with atoms. |
Translating Elixir/Erlang terms:
An application is equivalent of a windows DLL, something that you compose a system out of. A typical application would be a logging system.
Atoms are a non-garbage collected resource. They make convenient aliases to global things.
Doing the same with :a gives the erlang modules
| Letter | Module | Description |
| a | application | Generic OTP Application |
| application_controller | Kernel supplied application controller | |
| application_master | Kernel supplied application master. Responsible for knowing the topmost supervisor | |
| application_starter | Responsible for starting applications in a defined order | |
| array | Array structure, fixed or extensible | |
| atomics | Provides atomic operations using hardware instructions | |
| auth | Erlang network authentication server (deprecated) |
I have returned to this book now that the book is out of beta.
I also started using a different repo: https://github.com/chriseyre2000/property_testing
The only difference between my code and the samples is that I am using the pipe syntax where possible. My Execism.IO background in Elixir is also forcing me to make style changes to keep the code in Elixir format.
Part 1 chapter 4 does use the erlang queue library. It would be good to be able to get Elixir documentation on erlang packages.
The part 2 sample code is broken but I am working on fixing in my repo.
It turned out to be easier to download the code from the pragprog site.
I have continued working through this beta book and have updated the github repo: github.com/chriseyre2000/designing_elixir with the samples.
So far this book is easier to follow than say Programming Phoenix since it does not keep changing the code that you are working on. The testing code is normally close to where you have typed it, so finding mistakes does not require too much effort. I would recommend using mix test after each code sample has been typed in as fixing errors can be tricky.
Note the only difference between my code and the supplied sample is the use of the british name Maths rather than Math for the sample code. My degree is in Mathematics so I can’t let a typo like that stand!
The main points from the second half of the book are the very clean validation techniques used. I like that they called the process returned by start_link a session.
The book currently stops at the end of chapter 6, so I will have to resume work on this series once it has been updated.
Developer Rants 