Git error: command git clone failed - Host key verification failed

In case you encounter a git error like the following, please check your Gemfile for gems with :git attributes.

Problem

When using ssh URLS such as git@github.com:anynines/cfoundry_helper.git git will try to verify the remote host. This will fail since it is not possible to verify an unknown host's identity.

Git url making trouble:

gem "cfoundry_helper", :git => "git@github.com:anynines/cfoundry_helper.git"

Workaround

Use https git urls instead.

Git url working fine:

gem "cfoundry_helper", :git => "https://github.com/anynines/cfoundry_helper.git"

Example error message:

Staging error: failed to stage application:
Script exited with status 1
-----> Downloaded app package (4.1M)
Installing ruby.
-----> Using Ruby version: ruby-1.9.2
-----> Installing dependencies using Bundler version 1.3.2
 Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin --deployment
 Fetching gem metadata from https://rubygems.org/.........
 Fetching gem metadata from https://rubygems.org/..
 Fetching git@github.com:anynines/cfoundry_helper.git
 Host key verification failed.
 fatal: The remote end hung up unexpectedly
 Git error: command `git clone 'git@github.com:anynines/cfoundry_helper.git'
 "/tmp/staged/app/vendor/bundle/ruby/1.9.1/cache/bundler/git/cfoundry_helper-9abfb544196258e96b259e5bc5b7bdc676fe0c15"
 --bare --no-hardlinks` in directory /tmp/staged/app has failed.
 !
 ! Failed to install gems via Bundler.
 !
/var/vcap/packages/dea_next/buildpacks/lib/installer.rb:17:in `compile': Buildpack compilation step failed: (RuntimeError)
 from /var/vcap/packages/dea_next/buildpacks/lib/buildpack.rb:26:in `block in compile_with_timeout'
 from /usr/lib/ruby/1.9.1/timeout.rb:68:in `timeout'
 from /var/vcap/packages/dea_next/buildpacks/lib/buildpack.rb:25:in `compile_with_timeout'
 from /var/vcap/packages/dea_next/buildpacks/lib/buildpack.rb:16:in `block in stage_application'
 from /var/vcap/packages/dea_next/buildpacks/lib/buildpack.rb:12:in `chdir'
 from /var/vcap/packages/dea_next/buildpacks/lib/buildpack.rb:12:in `stage_application'
 from /var/vcap/packages/dea_next/buildpacks/bin/run:10:in `<main>'