Heroku destroys pg gem during deployment - ruby-on-rails

Question

I am attempting to deploy a Heroku application based on Ruby on Rails, and am having some issues. Although none of these issues existed in past deployments, Heroku randomly deletes the pg gem after deployment. This is my gemfile:
source 'https://rubygems.org'
git_source(:github) do |repo_name|
repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")
"https://github.com/#{repo_name}.git"
end
# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 5.1.3'
# User rails12 factor for heroku's native ruby support tweaks
gem 'rails_12factor'
# Use wdm for Windows poll changes
gem 'wdm', '>= 0.1.0' if Gem.win_platform?
# Use Puma as the app server
gem 'puma', '~> 3.7'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Bootstrap 3 for themeing and templating
gem 'bootstrap-sass'
# Use bootstrapformfor to allow forms to be auto-formatted as per bootstrap standards
gem 'bootstrap_form'
# Use JQuery code optimized for Bootstrap usage
gem 'jquery-rails'
# Use Dragonfly for image upload and handling
gem 'dragonfly', '~> 1.1.3'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.2'
# Turbolinks makes navigating your web application faster
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease
gem 'jbuilder', '~> 2.5'
# Use Devise for account management and authorization
gem 'devise'
# Use Cancancan for permissions enforcement
gem 'cancancan'
# Use rolify for role assignment to user accounts
gem 'rolify'
# Windows does not include zoneinfo files so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]
# Use ActiveModel has_secure_password
gem 'bcrypt', '~> 3.1.7'
group :development, :test do
# Call 'byebug' anywhere in the code to stop execution and get a debugger console
gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
# Adds support for Capybara system testing and selenium driver
gem 'capybara', '~> 2.13'
gem 'selenium-webdriver'
end
group :development do
# Access an IRB console on exception pages or by using <%= console %> anywhere in the code
gem 'web-console', '>= 3.3.0'
gem 'listen', '>= 3.0.5', '< 3.2'
# Spring speeds up development by keeping your application running in the background
gem 'spring'
gem 'spring-watcher-listen', '~> 2.0.0'
# Postgres for active record
gem 'pg'
end
Here is the deployment log:
-----> Ruby app detected
-----> Compiling Ruby/Rails
-----> Using Ruby version: ruby-2.3.4
###### WARNING:
Removing `Gemfile.lock` because it was generated on Windows.
Bundler will do a full resolve so native gems are handled properly.
This may result in unexpected gem versions being used in your app.
In rare occasions Bundler may not be able to resolve your dependencies at all.
https://devcenter.heroku.com/articles/bundler-windows-gemfile
-----> Installing dependencies using bundler 1.15.2
Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4
The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
Fetching gem metadata from https://rubygems.org/..........
Fetching version metadata from https://rubygems.org/..
Fetching dependency metadata from https://rubygems.org/.
Resolving dependencies...
Using rake 12.3.0
Using concurrent-ruby 1.0.5
Fetching minitest 5.11.1
Using thread_safe 0.3.6
Using builder 3.2.3
Using erubi 1.7.0
Using mini_portile2 2.3.0
Using crass 1.0.3
Using rack 2.0.3
Fetching nio4r 2.2.0
Using websocket-extensions 0.1.3
Using mini_mime 1.0.0
Using arel 8.0.0
Fetching public_suffix 3.0.1
Installing public_suffix 3.0.1
Installing minitest 5.11.1
Installing nio4r 2.2.0 with native extensions
Using execjs 2.7.0
Using bcrypt 3.1.11
Using rb-fsevent 0.10.2
Using ffi 1.9.18
Using bootstrap_form 2.7.0
Using bundler 1.15.2
Using cancancan 2.1.2
Using coffee-script-source 1.12.2
Using method_source 0.9.0
Using thor 0.20.0
Using orm_adapter 0.5.0
Fetching multi_json 1.13.1
Using puma 3.11.0
Using rails_serve_static_assets 0.0.5
Using rails_stdout_logging 0.0.5
Fetching rolify 5.2.0
Installing multi_json 1.13.1
Installing rolify 5.2.0
Using tilt 2.0.8
Fetching turbolinks-source 5.1.0
Using i18n 0.9.1
Using nokogiri 1.8.1
Installing turbolinks-source 5.1.0
Using tzinfo 1.2.4
Using rack-test 0.8.2
Using warden 1.2.7
Using sprockets 3.7.1
Using websocket-driver 0.6.5
Using mail 2.7.0
Fetching autoprefixer-rails 7.2.4
Fetching uglifier 4.1.3
Installing autoprefixer-rails 7.2.4
Installing uglifier 4.1.3
Using rb-inotify 0.9.10
Using coffee-script 2.4.1
Fetching addressable 2.5.2
Using rails_12factor 0.0.3
Using loofah 2.1.1
Using activesupport 5.1.4
Fetching turbolinks 5.1.0
Installing turbolinks 5.1.0
Installing addressable 2.5.2
Using sass-listen 4.0.0
Using rails-html-sanitizer 1.0.3
Using rails-dom-testing 2.0.3
Using globalid 0.4.1
Using activemodel 5.1.4
Using jbuilder 2.7.0
Fetching dragonfly 1.1.4
Fetching sass 3.5.5
Installing dragonfly 1.1.4
Installing sass 3.5.5
Using activejob 5.1.4
Using actionview 5.1.4
Using activerecord 5.1.4
Using actionpack 5.1.4
Using actionmailer 5.1.4
Using railties 5.1.4
Using sprockets-rails 3.2.1
Using coffee-rails 4.2.2
Using responders 2.4.0
Using jquery-rails 4.3.1
Fetching devise 4.4.0
Installing devise 4.4.0
Using bootstrap-sass 3.3.7
Using sass-rails 5.0.7
Using actioncable 5.1.4
Using rails 5.1.4
Bundle complete! 25 Gemfile dependencies, 72 gems now installed.
Gems in the groups development and test were not installed.
Bundled gems are installed into ./vendor/bundle.
Bundle completed (8.28s)
Cleaning up the bundler cache.
Removing rolify (5.1.0)
Removing turbolinks (5.0.1)
Removing autoprefixer-rails (7.1.6)
Removing sass (3.5.3)
Removing mime-types-data (3.2016.0521)
Removing nio4r (2.1.0)
Removing minitest (5.10.3)
Removing devise (4.3.0)
Removing mimemagic (0.3.2)
Removing cocaine (0.5.8)
Removing pg (0.21.0)
Removing uglifier (3.2.0)
Removing multi_json (1.12.2)
Removing paperclip (5.0.0)
Removing turbolinks-source (5.0.3)
Removing mime-types (3.1)
Removing climate_control (0.2.0)
The latest bundler is 1.16.1, but you are currently running 1.15.2.
To update, run `gem install bundler`
-----> Installing node-v6.11.1-linux-x64
-----> Detecting rake tasks
-----> Preparing app for Rails asset pipeline
Running: rake assets:precompile
rake aborted!
Gem::LoadError: Specified 'postgresql' for database adapter, but the gem is not loaded. Add `gem 'pg'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord).
ETCETCETC
Note how it randomly deletes the 'pg' gem after initial bundling. Could someone point me in the right direction?

Answer 1

Set your pg gem to require version 0.2x in your Gemfile:
gem 'pg', '~> 0.20'
What's happening is you're system is incorrectly attempting to use a newer, incompatible version of pg. pg 1.0.0 was released January 10, 2018, but it's not currently supported by rails. Since you aren't specifying which version of pg to use, you're system is trying to use the new version of pg, removing the old version, then failing.
See this rails issue, and this rails issue and this fix (Revert to pg 0.21.0 as Rails does not support pg 1.0.0 yet) for more discussion.

Answer 2

Put your pg gem out of development environment.

Answer 3

Remove gem pg from developement
group :development do
# Access an IRB console on exception pages or by using <%= console %> anywhere in the code
gem 'web-console', '>= 3.3.0'
gem 'listen', '>= 3.0.5', '< 3.2'
# Spring speeds up development by keeping your application running in the background
gem 'spring'
gem 'spring-watcher-listen', '~> 2.0.0'
end
and keep it outside from developement
# Postgres for active record
gem 'pg'

Answer 4

Try to the following
Remove gem 'pg' from group :development and keep that on Gemfile outside of group, then run bundler bundle update then follow these steps
git add .
git commit -m "Fixed gem pg issue"
git push heroku master
That will work
If you little bit confused again see the Heroku documentation and start from scratch
Thanks