Web Apps and MVC

These diagrams explain the flow of the web app for different use cases. These diagrams can easily be understood by stakeholders with no technical background. The conversation based on these diagrams are useful to understand the requirements and clarify any vague requirements.

This flow is also useful when developing a MVC based Web app. Because these use cases can span across different controllers and each controller can be shared by different use cases. It provides a structure and minimizes the rework required in later stages after the app is deployed.

You can read about

Dealing with Money in Rails Apps

Running Jobs in the Background

1. Active Job Async

Configure queue_adapter in config/application.rb:

config.active_job.queue_adapter = ActiveJob::QueueAdapters::AsyncAdapter.new 

  min_threads: 1,

  max_threads: 2 * Concurrent.processor_count,

  idletime: 600.seconds

2. Use perform_later when you send the email.

3. Linode $5 box has one core:

$ grep -c ^processor /proc/cpuinfo   

1

References

Rails Docs

Rails 5 Default Adapter
Rails Guides

Automatic Renewal LetsEncrypt SSL Certificate

sudo certbot renew --dry-run

If this does not show any errors, your SSL will be renewed automatically. Reference: 

How To Secure Apache with Let's Encrypt on Ubuntu 16.04

Install Wild Card SSL using LetsEncrypt on Apache

Run commands on server using Capistrano 3

Add :

require 'capistrano/console'

to Capfile

Now you can run:

bundle exec cap production console

This allows you to run commands on the server terminal. Useful to run commands like: uptime.

How to tail production log in Capistrano 3

1. Add:

to lib/capistrano/tasks/tail.rake.

namespace :logs do
  desc "tail rails logs. Usage cap production logs:tail_rails"
  task :tail_rails do
    on roles(:app) do
      execute "tail -f #{shared_path}/log/#{fetch(:rails_env)}.log"
    end
  end
end

2. You can now tail the production log from your local machine:

cap production logs:tail_rails

How to configure Capistrano 3 to play with Rails staging / production console

1. Add:

gem 'capistrano-rails-console', require: false

to Gemfile and bundle.

2. Add:

require 'capistrano/rails/console'

to Capfile.

3. Run:

cap production rails:console

to play in production rails console.

Make Capistrano Run Migration on Deploy

Make sure you have the db role in the 

config/deploy/production.rb file as follows:

:

server 'ip-address-goes-here', user: 'deploy-user', roles: %w{app web db}

Sending email in production in Rails apps

In controller:

PurchaseNotifierMailer.send_purchase_confirmation_email(@user).deliver!

In production.rb:

config.action_mailer.smtp_settings = {
  user_name: 'sendgridusername',
  password: 'sendgridpassword',
  domain: 'yourdomain.com',
  address: 'smtp.sendgrid.net',
  port: 587,
  authentication: :plain,
  enable_starttls_auto: true
}

Automatically Signin a User

sign_in(:user, @user)

Device Finger Printing

Errata for Articles on www.rubyplus.com

DK Smith has offered me his time to point out some errors, spelling mistakes etc. This page will document his findings.

Linode Box Images

git prompts for passphrase after mac os upgrade

Solution

1. Create (or edit if it exists) the following ~/.ssh/config file:
   

   Host *
     UseKeychain yes
     AddKeysToAgent yes
     IdentityFile ~/.ssh/id_rsa

2. eval "$(ssh-agent -s)" 

3. ssh-add -K ~/.ssh/id_rsa

Installing Rugged on Mac OS

Check if Mac is 64 bit: 

getconf LONG_BIT

ERROR: CMake is required to build Rugged

cat /Users/bparanj/.rvm/gems/ruby-2.3.1@headache/extensions/x86_64-darwin-17/2.3.0/rugged-0.25.1.1/gem_make.out

ERROR: CMake is required to build Rugged.

brew install cmake

Must be superuser to create this extension.

ALTER ROLE SUPERUSER;

createuser --superuser postgres2

gpg: keyserver receive failed: No route to host

Solution:

gpg-connect-agent --dirmngr 'keyserver --hosttable'

BYE

gpg --keyserver hkp://b4ckbone.de --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3 7D2BAF1CF37B13E2069D6956105BD0E739499BDB

When to Apply Memoization

Apply memoization, when two conditions are met:

1. Optimal sub structure
2. Overlapping sub problems

Make sure that `gem install libv8 -v '3.16.14.19' --source 'https://rubygems.org/'` succeeds before bundling.

This happened on Mac OS 10.10.5. I needed a specific version of libv8, so I used the -v flag in gem install.

Resolution

gem install libv8 -v 3.16.14.19 -- --with-system-v8

bundle config build.libv8 --with-system-v8

SSL Notes

git clone https://github.com/letsencrypt/letsencrypt
cd letsencrypt
./letsencrypt-auto --apache --rsa-key-size 4096


./letsencrypt-auto --apache -d example.com -d www.example.com -d foo.example.com -d bar.example.com -d baz.example.com


SSL with Let's Encrypt in Apache

Skill vs Challenge

When you work on improving your coding skill, be aware that you will experience these feelings that depends on your current skill level and the challenge level of the problem. Our goal is to be able to take on high challenges at a high skill level so that we can experience the Flow.