missing required flag heroku tail - ruby-on-rails

Question

I am working to deploy my rails app. Everything in running in local environment but I am having some issues making my first push to heroku. I am getting the standard app error, see pic:
when i run the command heroku logs --tail, i get the following error:
my gemfile is as so:
source 'https://rubygems.org'
# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.2.6'
# Use sqlite3 as the database for Active Record
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.1.0'
# See https://github.com/rails/execjs#readme for more supported runtimes
# gem 'therubyracer', platforms: :ruby
# Use jquery as the JavaScript library
gem 'jquery-rails'
# Turbolinks makes following links in your web application faster. Read more: https://github.com/rails/turbolinks
gem 'turbolinks'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.0'
# bundle exec rake doc:rails generates the API under doc/api.
gem 'sdoc', '~> 0.4.0', group: :doc
# Use ActiveModel has_secure_password
# gem 'bcrypt', '~> 3.1.7'
# Use Unicorn as the app server
# gem 'unicorn'
# Use Capistrano for deployment
# gem 'capistrano-rails', group: :development
group :development, :test do
# Call 'byebug' anywhere in the code to stop execution and get a debugger console
gem 'byebug'
end
group :development do
gem 'sqlite3'
# Access an IRB console on exception pages or by using <%= console %> in views
gem 'web-console', '~> 2.0'
group :production do
gem 'pg'
end
# Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
gem 'spring'
end
below are my heroku logs:
2
018-02-09T00:48:11.108425+00:00 app[web.1]: from /app/vendor/ruby-2.3.1/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:68:in `require'
2018-02-09T00:48:11.108427+00:00 app[web.1]: from /app/vendor/ruby-2.3.1/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:68:in `require'
2018-02-09T00:48:11.108435+00:00 app[web.1]: from bin/rails:3:in `load'
2018-02-09T00:48:11.108437+00:00 app[web.1]: from bin/rails:3:in `<main>'
2018-02-09T00:48:11.120606+00:00 app[web.1]: => Booting WEBrick
2018-02-09T00:48:11.120615+00:00 app[web.1]: => Rails 4.2.6 application starting in production on http://0.0.0.0:52651
2018-02-09T00:48:11.120619+00:00 app[web.1]: => Ctrl-C to shutdown server
2018-02-09T00:48:11.120618+00:00 app[web.1]: => Run `rails server -h` for more startup options
2018-02-09T00:48:11.120621+00:00 app[web.1]: Exiting
2018-02-09T00:49:30.407211+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=postcable.herokuapp.com request_id=ec520950-df52-44ee-95aa-890d9ad76949 fwd="67.20.250.6" dyno= connect= service= status=503 bytes= protocol=https
2018-02-09T00:49:32.372812+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=postcable.herokuapp.com request_id=ffdb944b-9293-4d96-8986-b0af2974704c fwd="67.20.250.6" dyno= connect= service= status=503 bytes= protocol=https

Answer 1

First of all, to get the log error to work correctly also pass a flag for your app name as well:
heroku logs --tail --app my_heroku_app_name
Also, it seems you have nested gem groups. I am assuming you are using postgresql as your database for production so I would recommend to move pg out of development>production group like so:
gem 'pg'
group :development do
gem 'sqlite3'
# Access an IRB console on exception pages or by using <%= console %> in views
gem 'web-console', '~> 2.0'
end
Then run
bundle install
Lastly, try pushing to heroku again with
git push heroku master

Answer 2

I solved, needed to define the PG version in my gemfile:
gem 'pg', '~> 0.18.4'