Separate health check endpoint using puma

Puma offers a way to query its internal stats by enabling a controll app in a separate port, this can be useful when we need to know if the app is alive, this is different than normal health check endpoints because it does not get processed by rails at all.

To enable this functionality, all you need to do is to add this line in your puma.rb file:

activate_control_app 'tcp://0.0.0.0:9293', { no_token: true }

It will start a second web server in the port 9293 that can be queried by monitoring tools or even balancer healthcheck.

ecruz@Edwins-MBP % curl 'http://127.0.0.1:9293/stats'
{"started_at":"2021-10-15T21:39:55Z","workers":2,"phase":0,"booted_workers":2,"old_workers":0,"worker_status":[{"started_at":"2021-10-15T21:39:55Z","pid":44969,"index":0,"phase":0,"booted":true,"last_checkin":"2021-10-15T21:40:05Z","last_status":{"backlog":0,"running":5,"pool_capacity":5,"max_threads":5,"requests_count":0}},{"started_at":"2021-10-15T21:39:55Z","pid":44970,"index":1,"phase":0,"booted":true,"last_checkin":"2021-10-15T21:40:05Z","last_status":{"backlog":0,"running":5,"pool_capacity":5,"max_threads":5,"requests_count":0}}]}%
ecruz@Edwins-MBP %

Check the documentation for more options/usages

Numberic separators JavaScript

Numberic separators is a new JavaScript feature that allows you to use underscores as separators to help to improve readability using a visual separation between groups of digits.

// A billion
const amount = 1_000_000_000;

// Hundreds of millions     
const amount = 1_475_938.38;

// 6234500 cents (62345 dollars)
const amount = 62345_00;

// 1,734,500
const amount = 1_734_500; 

// 20^30000
const amount = 2e30_000;

Javascript event loop

The event loop is the secret behind JavaScript's asynchronous programming. JS executes all operations on a single thread, but using a few smart data structures, it gives us the illusion of multi-threading but first we have to understand the Call Stack.

Call Stack

The call stack works based on the LIFO principle(last in first out) When you execute a script, the JavaScript engine creates a Global Execution Context and pushes it on top of the call stack.

function multiply(a, b) {
    return a * b
}

function squere(n) {
    return multiply(n, n)
}

function printSquere(n) {
    var result = squere(n)
    console.log(result)
}

printSquere(4)

**Stack**
4- multiply
3- squere
2- printSquere
1- main

Result: 16

Call Stack with async callbacks (Even loop)

The event loop facilitates this process; it constantly checks whether or not the call stack is empty. If it is empty, new functions are added from the event queue. If it is not, then the current function call is processed.

An example of this is the setTimeout method. When a setTimeout operation is processed in the stack, it is sent to the corresponding API which waits till the specified time to send this operation back in for processing.

console.log('hi')

setTimeout(()=> {
  console.log('there')
},5000)

console.log('bye')

**Stack**
3- there
2- bye
1- hi

**webapis**
setTimeout callback(cb)

**taskqueue**
callback(cb)

**evenloop**
move cb to stack

In the example the setTimeout Callback enters the webapi stack executes and then goes to the task queue and waits for the stack to become empty and the event loop moves the callback to the stack.

module_function

What it does?

• module_function allows exposing instance’s methods so they can be called as they would be class methods.

module User
  def name
    'Hello Sam'
  end
end

If you try to do this:

user = User.new
user.name

You're gonna receive an error because modules do not respond to the new method.

How can we use it?

You can use this useful method module_function:

module User
  module_function

  def name
    'Hello Sam'
  end
end

And call the name method like User.name

1. Use module_function to use all the methods inside a module as class methods or
2. Use module_function :name to only apply it in a specific method

A second option to do it

Another option to do so is using extend self instead:

module User
  extend self

  def name
    'Hello Sam'
  end
end

Truthy and Falsy Values

If JavaScript's built-in type coercion makes it true, thats mean that the values is a truthy.

  true
  {}
  []
  42
  "0"
  "false"
  new Date()
  -42
  12n
  3.14
  Infinity
  -Infinity

and in Javascript a falsy value is a value that is considered false

  false
  0
  0n: 0 as a BigInt
  '': Empty string
  null
  undefined
  NaN

Underscores are not allowed as part of domain names

According to rfc1035, underscores (_) are not allowed as part of domain names.

The labels must follow the rules for ARPANET host names. They must start with a letter, end with a letter or digit, and have as interior characters only letters, digits, and hyphen (-). There are also some restrictions on the length. Labels must be 63 characters or less.

This means domain names like my_domain.com or sub_domain.main-domain.com are invalid.

Special thanks to @jclopezdev for finding this out.

JavaScript null vs undefined

In JavaScript null and undefined are rather strange values, both serve a very similar purpose, which is to indicate the absence of a value.

Null

Null is used to assign a reference to an object that you will no longer need or, directly, you want to have the variable declared but initialize it with a value that you still do not know what it will be exactly. In all these cases the best thing to do is to assign a null value.

  var miVariable = null;
  console.log(miVariable);

//log null

undefined

For undefined means that the variable is declared but its value has not yet been defined.

  var miVariable
  console.log(miVariable);

//log null

Both values are values of type false, so if you do a non-strict comparison you will get true undefined, which means that the variable is declared but its value has not yet been defined.

if (null == undefined) {
  return true
 }
//log true

and if you do a strict comparison, because they are not really the same, it returns a false:

if (null === undefined) {
   return true
 }
return false
//log false

Javascript Hoisting

This means that variable and function declarations are physically moved to the beginning of the code and are allocated in memory during the compilation phase.

function welcomeTo(name) {
  console.log("Welcome to " + name);
}

welcomeTo("Magmalabs");
//returns welcome to magmalabs

As you can see hoisting allows you to use a function before declaring it in the code.

welcomeTo("Magmalabs");

function welcomeTo(name) {
  console.log("Welcome to " + name);
}
//returns welcome to magmalabs

And also allows you to use a function after declaring it in the code.

For variables, hoisting only applies to the declaration, not to their assignment. example:

We declare the variable name but we got an undefined

console.log(name); 
var name = magmalabs;
//return undefined

That’s because JavaScript only hoist the declaration

var name;

console.log(name); 
name = magmalabs;
//return undefined

To avoid these errors, it is very important to keep in mind that hoisting only applies to the declaration.

Profiles in docker compose, specify default services

It is common to have multiple services listed in the docker-compose file, sometimes with dependencies, but also, a normal workflow sometimes is to just start everything, like:

docker-compose -f docker-compose.yml -d

And it will start all servies listed with their dependencies, but, what happens if you need to add another service and you do not need it to start along with the rest? The answer is: profiles:

services:
  db:
    image: pg
  cache:
    image: redis
  rails:
    depends_on:
      - db
      - cache
    command: puma
  sidekiq:
    profiles: [ 'jobs' ]
    depends_on:
      - db
      - cache
    command: sidekiq

So, in this case, whenever you do docker-compose up -d it will start only rails with its dependencies: db and cache, it wont start sidekiq by default, but if you really want to start sidekiq, then you need to explicitly type it: docker-compose up sidekiq -d.

Eager load rails associations with nested scopes

It is common to apply some extra scopes when fetching AR relationships, for examples, if we have countries and states, we might want all the countries starting with the letter A and all their states that starts with the letter B, this will automatically create a n+1 query problem since it nees to iterate over each country and fetch all states, but, Rails provides a way to eager load these associations easily:

states_scope = State.where("name ilike 'b%'")
countries = Country.where("name ilike 'a%'")
# This is the magic
ActiveRecord::Associations::Preloader.new.preload(countries, :states, states_scope)

# Now you can invoke coutries.each(:states) and it wont cause queries N+1
countries.map {|country| { country.id => country.states.size }

Normally, you would have to define another relationship in order to eager load the association, but it is not needed using this approach:

class Country < AR::Base
  has_many :states
  has_many :states_starting_with_b, -> { where("name ilike 'b%'") }, foreign_key: :state_id, class_name: "State"
end

# Then
Country.includes(:states_starting_with_b).where("name ilike 'a%'")

But this approach does not scale, it requires to define tons of relationships

Docker compose services with health checks

If you need to add extra checks for services to be up and running before starting another one, you can use healtcheck property:

services:
  pg:
    image: pg/pg-12
    ports:
      - 5432:5432
    healtcheck:
      test: [ "CMD-SHELL", "pg_isready -U postgres" ]
      interval: 5s
      timeout: 5s
      retries: 5
  redis:
    image: redis:5.0.4-alpine
    ports:
      - 6380:6379
    healthcheck:
      test: [ "CMD", "redis-cli", "ping" ]
      interval: 5s
      timeout: 5s
      retries: 5
  app:
    image: railsapp
    depends_on:
      pg:
        condition: service_healthy
      redis:
        condition: service_healthy
    ports: ['3000:3000']
    command: |
      bash -c "bundle exec rails s"

Typeprof Ruby Interpreter in Ruby 3.0+

TypeProf is a Ruby interpreter that abstractly executes Ruby programs at the type level. It executes a given program and observes what types are passed to and returned from methods and what types are assigned to instance variables. All values are, in principle, abstracted to the class to which the object belongs, not the object itself.

Example: 1

 $ typeprof user.rb
# TypeProf 0.12.0

# Classes
class User
  attr_accessor skip_add_role: untyped
  def self.from_omniauth: (?Hash[bot, bot] auth) -> User

  private
  def assign_default_role: -> nil
end

Example 2:

 $ typeprof skill.rb
# TypeProf 0.12.0

# Classes
class Skill
  private
  def acceptable_image: -> nil
end

Example 3:

 $ typeprof ability.rb
# TypeProf 0.12.0

# Classes
class Ability
  attr_accessor user: untyped
  def initialize: (untyped user) -> untyped

  private
  def alias_actions: -> untyped
  def register_extension_abilities: -> untyped
end

Rollback a specific Rails migration

bundlde exec rails db:migrate:down VERSION=202101010000001

Where 202101010000001 is the migration you want to rollback

Rails + Facebook Oauth Locally with SSL

Recently I had the need to test Oauth with Facebook locally and after creating and configuring the App and everything was working wonderfully ...

until it was not.

Facebook now forces SSL so I had to setup it locally by creating a self signed certificate and running my server with it.

1. Create your certificate, this script create it as localhost.mumoc.crt and localhost.mumoc.key. Mumoc is my username in my working machine.

name=localhost.$(whoami)
openssl req \
  -new \
  -newkey rsa:2048 \
  -sha256 \
  -days 3650 \
  -nodes \
  -x509 \
  -keyout $name.key \
  -out $name.crt \
  -config <(cat <<-EOF
  [req]
  distinguished_name = req_distinguished_name
  x509_extensions = v3_req
  prompt = no
  [req_distinguished_name]
  CN = $name
  [v3_req]
  keyUsage = nonRepudiation, digitalSignature, keyEncipherment
  extendedKeyUsage = serverAuth
  subjectAltName = @alt_names
  [alt_names]
  DNS.1 = $name
  DNS.2 = *.$name
EOF
)

Make sure to at least add digitalSignature and keyEncipherment to KeyUsage or you won't be able to use it in Chrome

1. Trust the certificate (I moved it to a config/ssl directory inside my app folder)

mv localhost.mumoc.* config/ssl
sudo security add-trusted-cert -d -r trustRoot -k /Library/Keychains/System.keychain config/ssl/localhost.mumoc.crt

1. Run server binding the ssl with the key and certificate

rails s -b 'ssl://localhost:3000?key=config/ssl/localhost.mumoc.key&cert=config/ssl/localhost.mumoc.crt'

ON DUPLICATE KEY UPDATE

When you're doing an INSERT query, you could be trying to insert a row containing a primary key that already exists in the table. Instead of doing a previous query to see if the key exists or not, you could try ON DUPLICATE KEY UPDATE.

INSERT INTO table (
  field1, 
  field2
) 
VALUES (
  "foo", 
  "bar"
) 
ON DUPLICATE KEY UPDATE 
  field1="foo", 
  field2="bar"