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Table of Contents

  1. Usage TLDR
  2. Overview
  3. How it works
  4. Installing
  5. Workflow
  6. The Templates

Usage TLDR

gem install modulesync
msync --help


ModuleSync was written as a simple script with ERB templates to help the Puppet Labs module engineers manage the zoo of Puppet modules on GitHub, and has now been restructured and generalized to be used within other organizations. Puppet modules within an organization tend to have a number of meta-files that are identical or very similar between modules, such as the Gemfile, .travis.yml, .gitignore, or spec_helper.rb. If a file needs to change in one module, it likely needs to change in the same way in every other module that the organization manages.

One approach to this problem is to use sed in a bash for loop on the modules to make a single change across every module. This approach falls short if there is a single file that is purposefully different than the others, but still needs to be managed. Moreover, this approach does not help if two files are structured differently but need to be changed with the same meaning; for instance, if the .travis.yml of one module uses a list of environments to include, and another uses a matrix of includes with a list of excludes, adding a test environment to both modules will require entirely different approaches.

ModuleSync provides the advantage of defining a standard template for each file to follow, so it becomes clear what a file is supposed to look like. Two files with the same semantics should also have the same syntax. A difference between two files should have clear reasons, and old cruft should not be left in files of one module as the files of another module march forward.

Another advantage of ModuleSync is the ability to run in no-op mode, which makes local changes and shows the diffs, but does not make permanent changes in the remote repository.

How It Works

ModuleSync is a gem that uses the GitHub workflow to clone, update, and push module repositories. It expects to be activated from a directory containing configuration for modulesync and the modules, or you can pass it the location of this configuration directory. The configuration for the Puppet Labs modules, can be used as an example for your own configuration. The configuration directory contains a directory called moduleroot which mirrors the structure of a module. The files in the moduleroot are ERB templates, and MUST be named after the target file, with .erb. appended. The templates are rendered using values from a file called config_defaults.yml in the root (not moduleroot) of the configuration directory. The default values can be overridden or extended by adding a file called .sync.yml to the module itself. This allows us to, for example, have a set of "required" gems that are added to all Gemfiles, and a set of "optional" gems that a single module might add.

Within the templates, values can be accessed in the @configs hash, which is merged from the values under the keys :global and the target file name (no .erb suffix).

The list of modules to manage is in managed_modules.yml in the configuration directory. This lists just the names of the modules to be managed.

ModuleSync can be called from the command line with parameters to change the branch you're working on or the remote to clone from and push to. You can also define these parameters in a file named modulesync.yml in the configuration directory.


gem install modulesync

For developers:

gem build modulesync.gemspec
gem install modulesync-*.gem


Default mode

With no additional arguments, ModuleSync clones modules from the puppetlabs github organization and pushes to the master branch.

Make changes

Make changes to a file in the moduleroot. For sanity's sake you should commit and push these changes, but in this mode the update will be rendered from the state of the files locally.


Do a dry-run to see what files will be changed, added and removed. This clones the modules to modules/<namespace>-<modulename> in the current working directory, or if the modules are already cloned, does an effective git fetch origin; git checkout master; git reset --hard origin/master on the modules. Don't run modulesync if the current working directory contains a modules/ directory with changes you want to keep. The dry-run makes local changes there, but does not commit or push changes. It is still destructive in that it overwrites local changes.

msync update --noop

Offline support

The --offline flag was added to allow a user to disable git support within msync. One reason for this is because the user wants to control git commands external to msync. Note, when using this command, msync assumes you have create the folder structure and git repositories correctly. If not, msync will fail to update correctly.

msync update --offline

Damage mode

Make changes for real and push them back to master. This operates on the pre-cloned modules from the dry-run or clones them fresh if the modules aren't found.

msync update -m "Commit message"

Amend the commit if changes are needed.

msync update --amend

For most workflows you will need to force-push an amended commit. Not required for gerrit.

msync update --amend --force

Automating Updates

You can install a pre-push git hook to automatically clone, update, and push modules upon pushing changes to the configuration directory. This does not include a noop mode.

msync hook activate

If you have activated the hook but want to make changes to the configuration directory (such as changes to managed_modules.yml or modulesync.yml) without touching the modules, you can deactivate the hook.

msync hook deactivate

Submitting PRs/MRs to GitHub or GitLab

You can have modulesync submit Pull Requests on GitHub or Merge Requests on GitLab automatically with the --pr CLI option.

msync update --pr

In order for GitHub PRs or GitLab MRs to work, you must either provide the GITHUB_TOKEN or GITLAB_TOKEN environment variables, or set them per repository in managed_modules.yml, using the github or gitlab keys respectively.

For GitHub Enterprise and self-hosted GitLab instances you also need to set the GITHUB_BASE_URL or GITLAB_BASE_URL environment variables, or specify the base_url parameter in modulesync.yml:

    token: 'EXAMPLE_TOKEN'
    base_url: ''

    token: 'EXAMPLE_TOKEN'
    base_url: ''


  • Set the PR/MR title with --pr-title or in modulesync.yml with the pr_title attribute.
  • Assign labels to the PR/MR with --pr-labels or in modulesync.yml with the pr_labels attribute. NOTE: pr_labels should be a list. When using the --pr-labels CLI option, you should use a comma separated list.
  • Set the target branch with --pr-target-branch or in modulesync.yml with the pr_target_branch attribute.

More details for GitHub:

Using Forks and Non-master branches

The default functionality is to run ModuleSync on the puppetlabs modules, but you can use this on your own organization's modules. This functionality also applies if you want to work on a fork of the puppetlabs modules or work on a non-master branch of any organization's modules. ModuleSync does not support cloning from one remote and pushing to another, you are expected to fork manually. It does not support automating pull requests.


If you dry-run before doing the live update, you need to specify what namespace to clone from because the live update will not re-clone if the modules are already cloned. The namespace should be your fork, not the upstream module (if working on a fork).

msync update -n puppetlabs --noop

Damage mode

You don't technically need to specify the namespace if the modules are already cloned from the dry-run, but it doesn't hurt. You do need to specify the namespace if the modules are not pre-cloned. You need to specify a branch to push to if you are not pushing to master.

msync update -n puppetlabs -b sync_branch -m "Commit message"

Configuring ModuleSync defaults

If you're not using the puppetlabs modules or only ever pushing to a fork of them, then specifying the namespace and branch every time you use ModuleSync probably seems excessive. You can create a file called modulesync.yml in the configuration directory that provides these arguments automatically. This file has a form such as:

namespace: mygithubusername
branch: modulesyncbranch

Then you can run ModuleSync without extra arguments:

msync update --noop
msync update -m "Commit message"

Available parameters for modulesync.yml

  • git_base : The default URL to git clone from (Default: '')
  • namespace : Namespace of the projects to manage (Default: 'puppetlabs'). This value can be overridden in the module name (e.g. 'namespace/mod') or by using the namespace key for the module in managed_modules.yml.
  • branch : Branch to push to (Default: 'master')
  • remote_branch : Remote branch to push to (Default: Same value as branch)
  • message : Commit message to apply to updated modules.
  • pre_commit_script : A script to be run before commiting (e.g. 'contrib/')
  • pr_title : The title to use when submitting PRs/MRs to GitHub or GitLab.
  • pr_labels : A list of labels to assign PRs/MRs created on GitHub or GitLab.
namespace: MySuperOrganization
branch: modulesyncbranch
pr_title: "Updates to module template files via modulesync"
git_base: ''
namespace: MySuperOrganization
branch: modulesyncbranch
namespace: stackforge
git_base:  ssh://
branch: msync_foo
remote_branch: refs/publish/master/msync_foo

Filtering Repositories

If you only want to sync some of the repositories in your managed_modules.yml, use the -f flag to filter by a regex:

msync update -f augeas -m "Commit message"    # acts only on the augeas module
msync update -f puppet-a..o "Commit message"

If you want to skip syncing some of the repositories in your managed_modules.yml, use the -x flag to filter by a regex:

msync update -x augeas -m "Commit message"    # acts on all modules except the augeas module
msync update -x puppet-a..o "Commit message"

If no -f is specified, all repository are processed, if no -x is specified no repository is skipped. If a repository matches both -f and -x it is skipped.

Pushing to a different remote branch

If you want to push the modified branch to a different remote branch, you can use the -r flag:

msync update -r master_new -m "Commit message"

Automating updates

If you install a git hook, you need to tell it what remote and branch to push to. This may not work properly if you already have the modules cloned from a different remote. The hook will also look in modulesync.yml for default arguments.

msync hook activate -n puppetlabs -b sync_branch

Updating metadata.json

Modulesync can optionally bump the minor version in metadata.json for each modified modules if you add the --bump flag to the command line:

msync update -m "Commit message" --bump

Tagging repositories

If you wish to tag the modified repositories with the newly bumped version, you can do so by using the --tag flag:

msync update -m "Commit message" --bump --tag

Setting the tag pattern

You can also set the format of the tag to be used (printf-formatted) by setting the tag_pattern option:

msync update -m "Commit message" --bump --tag --tag_pattern 'v%s'

The default for the tag pattern is %s.

Updating the CHANGELOG

When bumping the version in metadata.json, modulesync can let you updating in each modified repository.

This is one by using the --changelog flag:

msync update -m "Commit message" --bump --changelog

This flag will cause the file to be updated with the current date, bumped (minor) version, and commit message.

If is absent in the repository, nothing will happen.

Working with templates

As mentioned, files in the moduleroot directory must be ERB templates (they must have an .erb extension, or they will be ignored). These files have direct access to @configs hash, which gets values from config_defaults.yml file and from the module being processed:

<%= @configs[:git_base] %>
<%= @configs[:namespace] %>
<%= @configs[:puppet_module] %>

Alternatively some meta data is passed to the template. This will allow you to add custom Ruby extensions inside the template, reading other files from the module, to make the template system more adaptive.

module: <%= @metadata[:module_name] %>
target: <%= @metadata[:target_file] %>
workdir: <%= @metadata[:workdir] %>

Will result in something like:

module: puppet-test
target: modules/github-org/puppet-test/test
workdir: modules/github-org/puppet-test

The Templates

See Puppet's modulesync_configs and Vox Pupuli's modulesync_config repositories for different templates currently in use.

Transfer Notice

This plugin was originally authored by Puppet Inc. The maintainer preferred that Vox Pupuli take ownership of the module for future improvement and maintenance. Existing pull requests and issues were transferred over, please fork and continue to contribute at



This gem is licensed under the Apache-2 license.

Release information

To make a new release, please do:

  • update the version in the gemspec file
  • Install gems with bundle install --with release --path .vendor
  • generate the changelog with bundle exec rake changelog
  • Check if the new version matches the closed issues/PRs in the changelog
  • Create a PR with it
  • After it got merged, push a tag. GitHub actions will do the actual release to rubygems and GitHub Packages