I find it very easy to keep track of all language features using cheat sheet.

I have been coding for the last 10 years. I have been through Quick Basic, Visual Basic, C, PHP, Ruby, Javascript and Web UI with CSS, HTML and Bootstrap. Its impossible for anyone to remember all the features and syntax of everything.

Then, I found https://ohmycheatsheet.com . It has everything I need like CSS, HTML, jQUery, Ruby and Javascript cheat sheets.

Some useful links are:-









Links to my new site shivab.com

Installing and configuration of Nginx Web/(Reverse proxy) server in ubuntu

First you will have to install ubuntu

$ sudo apt install nginx

this will install the software and it will generate default configurations in /etc/nginx/site-available folder. You can see those files there. You can modify the default.conf file. Default content is

# Default server configuration
server {
        listen 80 default_server;
        listen [::]:80 default_server;

        # SSL configuration
        # listen 443 ssl default_server;
        # listen [::]:443 ssl default_server;
        # Note: You should disable gzip for SSL traffic.
        # See: https://bugs.debian.org/773332
        # Read up on ssl_ciphers to ensure a secure configuration.
        # See: https://bugs.debian.org/765782
        # Self signed certs generated by the ssl-cert package
        # Don't use them in a production server!
        # include snippets/snakeoil.conf;

        root /var/www/html;

        # Add index.php to the list if you are using PHP
        index index.html index.htm index.nginx-debian.html;

        server_name _;

        location / {
                # First attempt to serve request as file, then
                # as directory, then fall back to displaying a 404.
                try_files $uri $uri/ =404;

        # pass PHP scripts to FastCGI server
        #location ~ \.php$ {
        #       include snippets/fastcgi-php.conf;
        #       # With php-fpm (or other unix sockets):
        #       fastcgi_pass unix:/var/run/php/php7.0-fpm.sock;
        #       # With php-cgi (or other tcp sockets):
        #       fastcgi_pass;

        # deny access to .htaccess files, if Apache's document root
        # concurs with nginx's one
        #location ~ /\.ht {
        #       deny all;

# Virtual Host configuration for example.com
# You can move that to a different file under sites-available/ and symlink that
# to sites-enabled/ to enable it.
#server {
#       listen 80;
#       listen [::]:80;
#       server_name example.com;
#       root /var/www/example.com;
#       index index.html;
#       location / {
#               try_files $uri $uri/ =404;
#       }

To configure reverse proxy

server {
  listen 80;
  listen [::]:80;

  server_name example.com;

  location / {
      proxy_pass http://localhost:3000/;

here, your application server is running at port 3000 in localhost.

Problems I faced

I was trying to serve the Rails app from folder other than /var/www like /root/projects/production/myapp dir, but the nginx could not render the app. It return the permission denined issue. I changed the owner of all the folders and files and also I changed the file permission to 777. But I failed.

So I moved the project to /var/www

How I Hosted Rails app

I moved the rails app to /var/www and set the permission to chmod -R 755 /myapp

node-pre-gyp ERR! build error | yarn install | Rails | Mac – Mojave

I encountered a series of errors when I tried to run my existing Rails5 app in my freshly installed macOS Mojave.

$ bundle exec rails s

this generated some errors like, node not found, then I installed node using brew.

$ brew install node


$ npm install yarn
$ yarn install 
gyp ERR! build error
gyp ERR! stack Error: `make` failed with exit code: 2
gyp ERR! stack     at ChildProcess.onExit (/Users/john/projects/sifaris/node_modules/node-gyp/lib/build.js:262:23)
gyp ERR! stack     at ChildProcess.emit (events.js:196:13)
gyp ERR! stack     at Process.ChildProcess._handle.onexit (internal/child_process.js:256:12)
gyp ERR! System Darwin 18.5.0
gyp ERR! command "/usr/local/Cellar/node/12.1.0/bin/node" "/Users/john/projects/sifaris/node_modules/node-gyp/bin/node-gyp.js" "rebuild" "--verbose" "--libsass_ext=" "--libsass_cflags=" "--libsass_ldflags=" "--libsass_library="
gyp ERR! cwd /Users/john/projects/sifaris/node_modules/node-sass
gyp ERR! node -v v12.1.0
gyp ERR! node-gyp -v v3.8.0
gyp ERR! not ok
$ bundle exec rails s
=> Booting Puma
=> Rails 5.2.3 application starting in development
=> Run `rails server -h` for more startup options
error Lockfile does not contain pattern: "yarn@^1.15.2"
error Couldn't find an integrity file
error Found 2 errors.

  Your Yarn packages are out of date!
  Please run `yarn install --check-files` to update.


$ rm yarn.lock
$ yarn cache clean
$ yarn install
$ yarn install v1.15.2

now it installs all the dependencies properly

bundle exec rails s
=> Booting Puma
=> Rails 5.2.3 application starting in development
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.12.1 (ruby 2.6.0-p0), codename: Llamas in Pajamas
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://localhost:3000
Use Ctrl-C to stop
yarn install v1.15.2

Rails | Apartment gem | Resets AR objects when tenant switched

I ran into a weird situation today. Active Record objects stored in vars are removed when I switched from one tenant to another on the fly. This will create a weird test-failing scenario and you never know why its happening.

def switch(name)

@customers = [1,2,3]
switch('shiva') do |name|
  puts name
  puts @customers

# Gives output
# shiva
# 1
# 2
# 3


but when I do this

@roles     = Role.all
@customers = org.branches
@list      = [1, 2]

puts 'Role count' + @roles.count.to_s
puts 'Customer count' + @customers.count.to_s
puts 'list count' + @list.count.to_s

puts '-------'
puts 'Role count' + @roles.count.to_s
puts 'Customer count' + @customers.count.to_s
puts 'list count' + @list.count.to_s

output is

Role count2
Customer count2
list count2
Role count0
Customer count0
list count2



# apartment-2.2.0/lib/apartment/adapters/abstract_adapter.rb
#   Switch to a new tenant
#   @param {String} tenant name
def switch!(tenant = nil)
  run_callbacks :switch do
    return reset if tenant.nil?

    connect_to_new(tenant).tap do

Rails : PaperTrail gem : Custom events to track fields changed

In my project, I was asked to keep track of changes in records. I found PaperTrails gem, and its found to be pretty useful.

But it lacks a straightforward feature to know the fields changed in that particular version. Then I thought to write custom event name so that I could grep the field_name I wish to check.

# == Schema Information
# Table name: tasks
#  id                :integer          not null, primary key
#  worker_id         :integer
#  customer_id       :integer
#  kind              :integer          default(0)
#  status            :integer          default(0)
#  note              :text
#  start_on          :datetime
#  complete_on       :datetime
#  started_on        :datetime
#  completed_on      :datetime
#  created_at        :datetime         not null
#  updated_at        :datetime         not null
#  driver_acceptance :integer          default(0)
#  refuel_id         :integer
#  shift_id          :integer

class Task < ActiveRecord::Base
  include Timeable
  # Update event-name on update
  before_save :paper_trail_events, on: :update

  enum status: { scheduled: 0, started: 1, skipped: 2, completed: 3, paused: 4, rescheduled: 5 }
  enum kind: { inter_location: 0, refuel: 1, break: 2 }
  enum driver_acceptance: { pending: 0, accepted: 1, rejected: 2, sent: 3 }


    def paper_trail_events
      changed_fields         = self.changes.keys - ['created_at', 'updated_at']
      self.paper_trail_event = "Updated #{changed_fields.join(',')}"

In Rails Console

> Task.find(1768).versions.map &:event
=> ["Updated start_on,complete_on,status", "Updated worker_id"]


Invalid CSS after “(min-width: “: expected expression (e.g.

Two possible reasons:

  • You might be @importing minified version of css assets like bootstrap.min.css
    • I did same and later solved using normal version css file
  • Search the suspect file if it has the content (min-width: and (max-width on the same line
    • see if there is any variable used
    • there might be px unit missing after the var
    • see if there is any possibility of var being nil
    • use @if condition to solve problem
    • eg:
@if  $min != null and $max != null{
  @media (min-width: $min + 'px') and (max-width: $max + 'px') {