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Jens is the Puppet modules/hostgroups librarian used by the [CERN IT department] (https://cern.ch/it). It is basically a Python toolkit that generates [Puppet environments] (https://docs.puppetlabs.com/puppet/latest/reference/environments.html) dynamically based on some input metadata. Jens is useful in sites where there are several administrators taking care of siloed services (mapped to what we call top-level "hostgroups", see below) with very service-specific configuration but sharing configuration logic via modules.
This tool covers the need of several roles that might show up in a typical shared Puppet infrastructure:
- Developers writing manifests who want an environment to test new code: Jens provides dynamic environments that automatically update with overrides for the modules being developed that point to development branches.
- Administrators who don't care: Jens supports simple dynamic environments that default to the production branch of all modules and that only update automatically when there's new production code.
- Administrators looking for extra stability who are reluctant to do rolling updates: Jens implements snapshot environments that are completely static and don't update unless redefined, as all modules are pinned by commit identifier.
Right now, the functionality is quite tailored to CERN IT's needs, however all contributions to make it more generic and therefore more useful for the community are more than welcome.
This program has been used as the production Puppet librarian at CERN IT since August 2013.
In Jens' realm, Puppet environments are basically a collection of modules, hostgroups, hierarchies of Hiera data and a site.pp. These environments are defined in environment definition files which are stored in a separate repository that's known to the program. Also, Jens makes use of a second metadata repository to know what modules and hostgroups are part of the library and are therefore available to generate environments.
With all this information, Jens produces a set of environments that can be used by Puppet masters to compile Puppet catalogs. Two types of environments are supported: dynamic and static. The former update automatically as new commits arrive to the concerned repositories whereas the latter keep static pointing to the specified commits to implement the concept of "configuration snapshot" (read the environments section for more information).
Jens is composed by several CLIs: jens-config, jens-gc, jens-reset, jens-stats and jens-update to perform different tasks. Manual pages are shipped for all of them.
Basically, the input data that's necessary for an execution of jens-update (the core tool provided by this toolset) is two Git repositories:
- The repository metadata repository (or the library)
- The environment definitions repository (or the environments)
More details about these are given in the following sections.
Jens uses a single YAML file stored in a Git repository to know what are the modules and hostgroups available to generate environments. Apart from that, it's also used to define the paths to two special Git repositories containing what's called around here the common Hiera data and the site manifest.
This is all set up via two configuration keys: repositorymetadata (which is
the directory containing a clone of the repository) and repositorymetadatadir
(the file itself).
The following is how a skeleton of the file looks like:
---
repositories:
common:
hieradata: http://git.example.org/pub/it-puppet-common-hieradata
site: http://git.example.org/pub/it-puppet-site
hostgroups:
...
aimon: http://git.example.org/pub/it-puppet-hostgroup-aimon
cloud: http://git.example.org/pub/it-puppet-hostgroup-cloud
...
modules:
...
apache: http://git.example.org/pub/it-puppet-module-apache
bcache: http://git.example.org/pub/it-puppet-module-bcache
...
The idea is that when a new top-level hostgroup is added or a new module is needed this file gets populated with the corresponding clone URLs of the repositories. Jens will add new elements to all the environments that are entitled to get them during the next run of jens-update.
Another example is available in examples/repositories/repositories.yaml.
There are two bits that are declared via the library file that require some extra clarifications, especially because they are fundamentally traversal to the rest of the declarations and are maybe a bit hardcoded to how our Puppet infrastructure is designed.
The repository pointed to by site must contain a single manifest called site.pp that serves as the catalog compilation entrypoint and therefore where all the hostgroup autoloading (explained later) takes place.
it-puppet-site/
├── code
│ └── site.pp
└── README
OTOH, the common hieradata is a special repository that hosts different types of Hiera data to fill the gaps that can't be defined at hostgroup or module level (operating system, hardware vendor and environment dependent keys). The following is an example of how the hierarchy in there should look like.
it-puppet-common-hieradata/
├── data
│ ├── common.yaml
│ ├── environments
│ │ ├── production.yaml
│ │ └── qa.yaml
│ ├── hardware
│ │ └── vendor
│ │ ├── foovendor.yaml
│ │ └── ...
│ └── operatingsystems
│ └── RedHat
│ ├── 5.yaml
│ ├── 6.yaml
│ └── 7.yaml
└── README
common.yaml is the most generic Hiera data YAML file of all the hierarchy as it's visible for all nodes regardless of their hostgroup, environment, hardware type and operatingsystem. It's useful to define very top-level keys.
Working examples of both repositories (used during the installation tutorial later on) can be found in the following locations
- examples/example-repositories/common-hieradata
- examples/example-repositories/site
Also, an example of a Hiera hierarchy configuration file that matches this structure is available on examples/hiera.yaml.
Each module/hostgroup lives in a separate Git repository, which contains two top-level directories: code and data.
- code: this is where the actual Puppet code resides, basically where the manifests, lib, files and templates directories live.
- data: all the relevant Hiera data is stored here. For modules, there's only one YAML file named after the module.
Example:
it-puppet-module-lemon/
├── code
│ ├── lib
│ │ └── facter
│ │ ├── configured_kernel.rb
│ │ ├── lemon_exceptions.rb
│ │ └── ...
│ ├── manifests
│ │ ├── config.pp
│ │ ├── init.pp
│ │ ├── install.pp
│ │ ├── klogd.pp
│ │ ├── las.pp
│ │ └── ...
│ ├── Modulefile
│ ├── README
│ └── templates
│ └── metric.conf.rb
└── data
└── lemon.yaml
For those already wondering how we manage to keep track of upstream modules with this strutucture: Git subtree :)
Hostgroups are just Puppet modules that are a bit special, allowing us to automatically load Puppet classes based on the hostgroup a given host belongs to (information which is fetched at compilation time from an ENC).
This is a CERNism and unfortunately we're not aware of anybody in the Puppet community doing something similar. However, we found this idea very useful to classify IT services, grouping machines belonging to a given service in the same top-level hostgroup. Modules are normally included in the hostgroup manifests (along the hierarchy) and configured via Hiera.
In short, hostgroups represent the service-specific configuration and modules are reusable "blocks" of code that abstract certain recurrent configuration tasks which are typically used by several hostgroups.
Getting back to the structure itself, the code directory serves the same purpose as the one for modules, however the data one is slightly different, as it contains FQDN-specific Hiera data for hosts belonging to this hostgroup and data that applies at different levels of the hostgroup hierarchy.
Next, a partial example of a real-life hostgroup and its subhostgroups with the corresponding manifests and Hiera data:
it-puppet-hostgroup-punch/code/manifests/
├── aijens
│ ├── app
│ │ └── live.pp
│ ├── app.pp
...
├── init.pp
it-puppet-hostgroup-punch/data/hostgroup
├── punch
│ ├── aijens
│ │ ├── app
│ │ │ ├── live
│ │ │ │ └── primary.yaml
│ │ │ └── live.yaml
│ │ └── app.yaml
│ ├── aijens.yaml
...
└── punch.yaml
it-puppet-hostgroup-punch/data/fqdns/
├── foo1.cern.ch.yaml
For instance, if foo1.cern.ch belonged to punch/aijens/app/live, it'd be entitled to automatically include init.pp, aijens.pp (which does no exist in this case), app.pp and live.pp. Also, Hiera keys will be looked up using files foo1.cern.ch.yaml, punch.yaml, aijens.yaml, app.yaml and live.yaml
To avoid clashes during the autoloading with modules that might have the same name, the top-most class of the hostgroup is prefixed with hg_.
~ $ grep ^class it-puppet-hostgroup-punch/code/manifests/aijens/app.pp
class hg_punch::aijens::app {
~ $ grep ^class it-puppet-hostgroup-punch/code/manifests/init.pp
class hg_punch {
There's more information about how this all works filesystem-wise below. An example of the autoloading mechanism can be found in the example site.pp mentioned above.
One of the parameters that can be configured via the configuration file is the
path to a clone of the Git repository containing the environment definitions
(configuration key environmentsmetadatadir). Each file with .yaml extension
is a candidate environment and will be considered by Jens during the update cycle.
An example of a very simple one can be located in examples/environments.
That said, environments are mostly useful for development, for instance to validate the effect of a change in an specific module using the stable version of the remaining configuration. This is accomplished by using environment overrides:
~/it-puppet-environments $ cat devticket34.yaml
---
default: master
notifications: higgs@example.org
overrides:
modules:
apache: dev34
See ENVIRONMENTS.md for further details on this subject, including how to create configuration snapshots instead of dynamic environments :)
Environments are cool to quickly get a development sandbox. They go in and out in a very rapid fashion, as new features are needed or finished. However, these are indeed not ideal for production nodes. Because of this, it's also interesting to have some kind of special environments and use them as the place where all the code converges at some point after development/testing/QA and place the bulk of the service there.
This section is just a recommendation that describes how things are done over here, however Jens does not enforce the existence or the structure of any environment at all.
In our site there's the concept of golden environment. These are long-lived, simple and unmodifiable dynamic environments used for production and QA (mandatory for all changes in modules impacting several unrelated services). The following are the definitions:
~/it-puppet-environments $ cat production.yaml qa.yaml
---
default: master
notifications: higgs@example.org
---
default: qa
notifications: higgs@example.org
As you can see, these are very simple environments that collect all the master
and qa branches of all modules and hostgroups available in the library. This
of course relies on one of our internal policies that say that all the
repositories containing Puppet code must have at least two branches: master
and qa, meaning that they will always be expanded by Jens. This behaviour can
be configured by the mandatorybranches configuration key.
As environment definitions are just Yaml files, the files can be easily protected from unauthorized/accidental modification via, for instance, Gitolite rules :)
Internally, Jens uses different directories to keep track of what's going on
with the Git repositories it has to be aware of. There's one called clone
that contains a checked out working tree of all the branches that are necessary
by environments for a each module/hostgroup. This way, an environment is just a
collection of symbolic links to these directories, which targets depend on the
environment definition. As an example, this is how the whole tree for the
hypothetical environment devticket34 declared previously would look like:
environments/devticket34/
├── hieradata
│ ├── common.yaml -> ../../../clone/common/hieradata/master/data/common.yaml
│ ├── environments -> ../../../clone/common/hieradata/master/data/environments
│ ├── fqdns
│ │ ├── aimon -> ../../../../clone/hostgroups/aimon/master/data/fqdns
│ │ ├── cloud -> ../../../../clone/hostgroups/cloud/master/data/fqdns
│ │ └── ...
│ ├── hardware -> ../../../clone/common/hieradata/master/data/hardware
│ ├── hostgroups
│ │ ├── aimon -> ../../../../clone/hostgroups/aimon/master/data/hostgroup
│ │ ├── cloud -> ../../../../clone/hostgroups/cloud/master/data/hostgroup
│ │ └── ...
│ ├── module_names
│ │ ├── apache -> ../../../../clone/modules/apache/dev34/data
│ │ ├── bcache -> ../../../../clone/modules/apache/bcache/data
│ │ └── ...
│ └── operatingsystems -> ../../../clone/common/hieradata/master/data/operatingsystems
├── hostgroups
│ ├── hg_aimon -> ../../../clone/hostgroups/aimon/master/code
│ ├── hg_cloud -> ../../../clone/hostgroups/cloud/master/code
│ └── hg_...
├── modules
│ ├── apache -> ../../../clone/modules/apache/dev34/code
│ ├── bcache -> ../../../clone/modules/apache/master/code
│ └── ...
└── site -> ../../clone/common/site/master/code
As shown, the master branch of all available repositories are used (as the default dictates) however the module apache has been overridden to use a different one.
Environments will be written to the directory specified by the configuration
key environmentsdir.
It's an execution of jens-update, which is normally trigged by a cronjob. It will determine what's new, what branches have to be updated and what environments have to be created/modified/deleted. The following is an example of what's typically found in the log files after a run where there was not much to do (a hostgroup got new code in the QA branch and a new environment was created):
INFO Obtaining lock 'aijens' (attempt: 1)...
INFO Refreshing metadata...
INFO Setting 'aijens' lock TTL to 8 secs...
INFO Refreshing repositories...
INFO Fetching repositories inventory...
INFO Refreshing bare repositories (modules)
INFO New repositories: []
INFO Deleted repositories: []
INFO Setting 'aijens' lock TTL to 1040 secs...
INFO Cloning and expanding NEW bare repositories...
INFO Expanding EXISTING bare repositories...
INFO Purging REMOVED bare repositories...
INFO Refreshing bare repositories (hostgroups)
INFO New repositories: []
INFO Deleted repositories: []
INFO Setting 'aijens' lock TTL to 600 secs...
INFO Cloning and expanding NEW bare repositories...
INFO Expanding EXISTING bare repositories...
INFO Updating ref '/mnt/puppet/aijens-3afegt67.cern.ch/clone/hostgroups/vocms/qa'
INFO Purging REMOVED bare repositories...
INFO Refreshing bare repositories (common)
INFO New repositories: []
INFO Deleted repositories: []
INFO Setting 'aijens' lock TTL to 8 secs...
INFO Cloning and expanding NEW bare repositories...
INFO Expanding EXISTING bare repositories...
INFO Purging REMOVED bare repositories...
INFO Persisting repositories inventory...
INFO Executed 'refresh_repositories' in 6287.78 ms
INFO Refreshing environments...
INFO New environments: ['am1286']
INFO Existing and changed environments: []
INFO Deleted environments: []
INFO Setting 'aijens' lock TTL to 2 secs...
INFO Creating new environments...
INFO Creating new environment 'am1286'
INFO Processing modules...
INFO Processing hostgroups...
INFO hostgroups 'aimon' overridden to use treeish 'am1286'
INFO Processing site...
INFO Processing common Hiera data...
INFO Purging deleted environments...
INFO Recreating changed environments...
INFO Refreshing not changed environments...
INFO Executed 'refresh_environments' in 1395.03 ms
INFO Releasing lock 'aijens'...
INFO Done
See INSTALL.md
As mentioned before, Jens, as it is now, is very coupled to the Puppet deployment that it was designed to work with. Probably the main goal we're trying to achieve making it free software is to try to attract the interest of more Puppeteers so we can all together improve the tool and make it useful for as many Puppet installations out there as we possibly can.
Hence, we'd be more than happy to get contributions of any kind! Feel free to submit bug reports and pull requests via Github.
There's also a DEVELOPERS.md that explains how to run the testsuite that is available for developers.
Jens has been written and it's currently being maintained by Nacho Barrientos, however it has been designed the way it is and has evolved thanks to the feedback provided by staff of the CERN IT department.
See COPYING
Jens was named after M. Jens Vigen, CERN's librarian.