Can not install gem 'pg' to deploy rails app to heroku

Question

I am trying to deploy my rails app to heroku and have replaced my gem 'sqlite3' with gem 'pg'. I have done this because I was getting an error trying to push my git to my heroku saying sqlite3 is not supported. whenever I try to run bundle install I get this error.

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    /Users/ipbyrne/.rvm/rubies/ruby-2.2.1/bin/ruby -r ./siteconf20150722-14766-1b3cg9.rb extconf.rb
checking for pg_config... no
No pg_config... trying anyway. If building fails, please try again with
 --with-pg-config=/path/to/pg_config
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
    --with-opt-dir
    --without-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/Users/ipbyrne/.rvm/rubies/ruby-2.2.1/bin/$(RUBY_BASE_NAME)
    --with-pg
    --without-pg
    --enable-windows-cross
    --disable-windows-cross
    --with-pg-config
    --without-pg-config
    --with-pg_config
    --without-pg_config
    --with-pg-dir
    --without-pg-dir
    --with-pg-include
    --without-pg-include=${pg-dir}/include
    --with-pg-lib
    --without-pg-lib=${pg-dir}/lib

extconf failed, exit code 1

Gem files will remain installed in /Users/ipbyrne/.rvm/gems/ruby-2.2.1/gems/pg-0.18.2 for inspection.
Results logged to /Users/ipbyrne/.rvm/gems/ruby-2.2.1/extensions/x86_64-darwin-14/2.2.0-static/pg-0.18.2/gem_make.out
An error occurred while installing pg (0.18.2), and Bundler cannot continue.
Make sure that `gem install pg -v '0.18.2'` succeeds before bundling.

Here is what my Gemfile looks like

source 'https://rubygems.org'


# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.0.0'

# Use sqlite3 as the database for Active Record
gem 'pg'

# Use SCSS for stylesheets
gem 'sass-rails', '~> 4.0.0'

# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'

# Use CoffeeScript for .js.coffee assets and views
gem 'coffee-rails', '~> 4.0.0'

# See https://github.com/sstephenson/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', '~> 1.2'

group :doc do
  # bundle exec rake doc:rails generates the API under doc/api.
  gem 'sdoc', require: false
end

gem 'devise', '~> 3.3.0'

gem 'bootstrap-sass', '~> 3.2.0.2'

gem 'acts_as_votable', '~> 0.10.0'

gem 'simple_form', '~>3.0.2'


# Use ActiveModel has_secure_password
# gem 'bcrypt-ruby', '~> 3.0.0'

# Use unicorn as the app server
# gem 'unicorn'

# Use Capistrano for deployment
# gem 'capistrano', group: :development

# Use debugger
# gem 'debugger', group: [:development, :test]

And here is the error I get whenever i try to manually install the gem running 'gem install pg -v '0.18.2' like it says at the end of the first error.

Building native extensions.  This could take a while...
ERROR:  Error installing pg:
    ERROR: Failed to build gem native extension.

    /Users/ipbyrne/.rvm/rubies/ruby-2.2.1/bin/ruby -r ./siteconf20150722-14778-10kqj2o.rb extconf.rb
checking for pg_config... no
No pg_config... trying anyway. If building fails, please try again with
 --with-pg-config=/path/to/pg_config
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
    --with-opt-dir
    --without-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/Users/ipbyrne/.rvm/rubies/ruby-2.2.1/bin/$(RUBY_BASE_NAME)
    --with-pg
    --without-pg
    --enable-windows-cross
    --disable-windows-cross
    --with-pg-config
    --without-pg-config
    --with-pg_config
    --without-pg_config
    --with-pg-dir
    --without-pg-dir
    --with-pg-include
    --without-pg-include=${pg-dir}/include
    --with-pg-lib
    --without-pg-lib=${pg-dir}/lib

extconf failed, exit code 1

Gem files will remain installed in /Users/ipbyrne/.rvm/gems/ruby-2.2.1/gems/pg-0.18.2 for inspection.
Results logged to /Users/ipbyrne/.rvm/gems/ruby-2.2.1/extensions/x86_64-darwin-14/2.2.0-static/pg-0.18.2/gem_make.out

Answer 1

You're missing the development headers which come in the libpq-dev package. That needs to be installed through whatever package manager you use (or if you're using a mac you can just do brew install postgresql)