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The gem manifest is an older way to specify gem files. It has issues managing gem dependencies, and has been replaced by Bundler. When a new version of the app is pushed to Heroku, any changes to the
.gems file are detected and new gems are installed along with their dependencies.
Creating a gem manifest
The gems manifest is a simple text file that includes information about each of
the gems required by an application. Each entry in the manifest includes a
mandatory gem name along with optional
source options. The
following is an example
.gems manifest file that includes two gems:
hpricot --version '>= 0.2' --source code.whytheluckystiff.net dm-core --version 0.9.10 formtastic --ignore-dependencies
--source options have short forms just like the
gem command; use
Each line of the
.gems file includes the following:
The name of the gem, as would be specified on the
gem installcommand line.
An optional gem version specifier. This can be a basic version number like
"0.1.2"or an advanced version specifier with comparison constraints like
">= 0.1.2"(see Specifying Versions in the RubyGems manual for more information). When no explicit version is specified, the most recent version of the gem is installed.
An optional gem repository source URL, like
gems.rubyforge.orgrepository is always included as the last source. Multiple
--sourcearguments may be provided for cases where dependencies cross multiple repositories.
An optional flag to ignore installing dependencies. This can be used to manually specify gem dependencies if they’re causing conflicts.
Deploying gem changes
.gems manifest file is added or modified, it must be committed to the
app’s git repository and pushed to Heroku for changes to take effect. The actual
gem install process occurs during the
git push operation.
The following example adds a
.gems file to the app’s git repository, commits
it, and pushes to the remote heroku repository:
$ git add .gems $ git commit -m 'added gems manifest file' $ git push heroku Counting objects: 4, done. Compressing objects: 100% (3/3), done. Writing objects: 100% (3/3), 356 bytes, done. Total 3 (delta 1), reused 0 (delta 0) -----> Heroku receiving push -----> Installing gem hpricot >= 0.2 from http://code.whytheluckystiff.net Building native extensions. This could take a while... Successfully installed hpricot-0.6 1 gem installed -----> Installing gem dm-core 0.9.10 from http://gems.rubyforge.org Successfully installed addressable-2.0.2 Successfully installed extlib-0.9.10 Successfully installed data_objects-0.9.11 Successfully installed dm-core-0.9.10 4 gems installed -----> Rails app detected Compiled slug size is 4.3MB -----> Launching.............. done App deployed to Heroku To firstname.lastname@example.org:vivid-moon-60.git 91425e3..fe10e87 master -> master
The push is aborted if the gem manifest is invalid or a gem fails to install, ensuring that an application is not deployed in an inconsistent state.