Brian Racer anveo

Falsehoods programmers believe about time

This is a compiled list of falsehoods programmers tend to believe about working with time.

Don't re-invent a date time library yourself. If you think you understand everything about time, you're probably doing it wrong.

Falsehoods

There are always 24 hours in a day.
February is always 28 days long.
Any 24-hour period will always begin and end in the same day (or week, or month).

Scaling your API with rate limiters

The following are examples of the four types rate limiters discussed in the accompanying blog post. In the examples below I've used pseudocode-like Ruby, so if you're unfamiliar with Ruby you should be able to easily translate this approach to other languages. Complete examples in Ruby are also provided later in this gist.

In most cases you'll want all these examples to be classes, but I've used simple functions here to keep the code samples brief.

Request rate limiter

This uses a basic token bucket algorithm and relies on the fact that Redis scripts execute atomically. No other operations can run between fetching the count and writing the new count.

If you want a run-down of the 1.3 changes and the design decisions behidn those changes, check out the LonestarElixir Phoenix 1.3 keynote: https://www.youtube.com/watch?v=tMO28ar0lW8

To use the new phx.new project generator, you can install the archive with the following command:

$ mix archive.install https://github.com/phoenixframework/archives/raw/master/phx_new.ez

Bump your phoenix dep

Phoenix v1.3.0 is a backwards compatible release with v1.2.x. To upgrade your existing 1.2.x project, simply bump your phoenix dependency in mix.exs:

A composable pattern for pure state machines with effects

State machines are everywhere in interactive systems, but they're rarely defined clearly and explicitly. Given some big blob of code including implicit state machines, which transitions are possible and under what conditions? What effects take place on what transitions?

There are existing design patterns for state machines, but all the patterns I've seen complect side effects with the structure of the state machine itself. Instances of these patterns are difficult to test without mocking, and they end up with more dependencies. Worse, the classic patterns compose poorly: hierarchical state machines are typically not straightforward extensions. The functional programming world has solutions, but they don't transpose neatly enough to be broadly usable in mainstream languages.

Here I present a composable pattern for pure state machiness with effects,

	DROP TABLE if exists d_date;

	CREATE TABLE d_date
	(
	date_dim_id INT NOT NULL,
	date_actual DATE NOT NULL,
	epoch BIGINT NOT NULL,
	day_suffix VARCHAR(4) NOT NULL,
	day_name VARCHAR(9) NOT NULL,
	day_of_week INT NOT NULL,

	require 'sidekiq/api'

	# 1. Clear retry set

	Sidekiq::RetrySet.new.clear

	# 2. Clear scheduled jobs

	Sidekiq::ScheduledSet.new.clear

	# 1: Use ruby 2.3.3 as base:
	FROM ruby:2.3.3

	RUN apt-get update -qq && apt-get install -y build-essential libpq-dev

	# 2: We'll set the application path as the working directory
	WORKDIR /usr/src/app

	# 3: We'll set the working dir as HOME and add the app's binaries path to $PATH:
	ENV HOME=/usr/src/app PATH=/usr/src/app/bin:$PATH

	<!DOCTYPE html>
	<html lang="en" dir="ltr">
	<head>
	<meta charset="UTF-8">
	<title>Ionic App</title>
	<meta name="viewport"
	content="width=device-width, initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0, user-scalable=no">
	<meta name="format-detection" content="telephone=no">
	<meta name="msapplication-tap-highlight" content="no">

	# Count total EBS based storage in AWS
	aws ec2 describe-volumes \| jq "[.Volumes[].Size] \| add"
	# Count total EBS storage with a tag filter
	aws ec2 describe-volumes --filters "Name=tag:Name,Values=CloudEndure Volume qjenc" \| jq "[.Volumes[].Size] \| add"
	# Describe instances concisely
	aws ec2 describe-instances \| jq '[.Reservations \| .[] \| .Instances \| .[] \| {InstanceId: .InstanceId, State: .State, SubnetId: .SubnetId, VpcId: .VpcId, Name: (.Tags[]\|select(.Key=="Name")\|.Value)}]'
	# Wait until $instance_id is running and then immediately stop it again
	aws ec2 wait instance-running --instance-id $instance_id && aws ec2 stop-instances --instance-id $instance_id

	# Get 10th instance in the account

	gem 'stackprof', require: false
	gem 'ruby-prof', require: false