You are browsing a read-only backup copy of Wikitech. The live site can be found at wikitech.wikimedia.org

Puppet coding: Difference between revisions

From Wikitech-static
Jump to navigation Jump to search
imported>Giuseppe Lavagetto
(→‎WMF Design conventions: Decommission classes are useless, don't suggest we should write them as we don't.)
imported>BCornwall
(BCornwall moved page Puppet coding to Puppet/Coding and style guidelines: Organizing Puppet-related items under one parent)
 
(52 intermediate revisions by 33 users not shown)
Line 1: Line 1:
This page is about writing puppet code:  how to write it, when to write it, where to put it.  For information about how to install or manage puppet, visit [[Puppet | this page]].
#REDIRECT [[Puppet/Coding and style guidelines]]
 
==Getting the source==
As simple as
git clone https://gerrit.wikimedia.org/r/p/operations/puppet
 
= When we use puppet =
 
Puppet is our configuration management system. Anything related to the configuration files & state of a server should be puppetized. There are a few cases where configurations are deployed into systems without involving puppet but these are the exceptions rather than the rule ([[How_to_deploy_code|MediaWiki configuration]], Squid configurations etc.); all package installs and configurations should happen via puppet in order to ensure peer review and reproducibility.
 
However, Puppet is ''not'' being used as a deployment system at Wikimedia. Pushing code via puppet, e.g. with git::clone should be avoided. Depending on the case, Debian packages or the use of our deployment system ([[Git-deploy]]) should be employed. Nowadays, deploying software via Trebuchet/git-deploy can be achieved in puppet by using the 'trebuchet' package provider.
 
== labs ==
 
Labs users have considerable leeway in the configuration of their systems, and the state of labs machines is frequently not puppetized.  Specific projects (e.g. toollabs) often have their own systems for maintaining code and configuration.
 
That said, any labs system being used for semi-production purposes (e.g. public test sites, bot hosts, etc.) should be fully puppetized. Labs users should always be ready for their instance to vanish at a moment's notice, and have a plan to reproduce the same functionality on a new instance -- generally this is accomplished using puppet.
 
The node definition for a labs machine is not stored in site.pp -- it lives in LDAP, and can be configured via a web interface on the instance configuration page.
 
= Style, organization and class conventions =
 
== Organization ==
 
Our code is, as of November 2014, in [[Puppet Todo | transition]] from a system of global manifests to a system of modules and roles.  Ultimately our code should be organized like this:
 
#  Nodes defined in site.pp can include role classes. They should avoid defining non-role classes; if that is happening then you probably need to create a role.
#  Use of global variables is highly discouraged.  A few actually global settings (e.g. $::site, $::realm) will crop up, but we probably don't need any new ones.
#  All manifests are declared inside modules.
#  Role classes are never parameterized, and all the classes they include are only configured using [[Puppet_Hiera|hiera]]. When using hiera, you can simply declare the class parameters in the relevant yaml file. This also allows dropping $::site-specific role classes or branches in classes, either depending on $::site, $::realm, etc. Old parametrization relied on using node-scope variables (e.g. $cluster) which had a default value as a top-scope variable. That should go away as soon as possible.
# All "main" roles - that is, the ones we apply directly to a server, as opposed to things like role::ntp or role::diamond - should include the standard class, that does most of the boilerplate base install of the system.
 
=== Nodes in site.pp ===
 
Our traditional node definitions included a lot of global variables and boilerplate that needed to be added. Nowadays, your node definitions should be as simple as possible, so ideally the must just include one role definition:
 
<source lang="ruby">
node 'redis01.codfw.wmnet' {
    role db::redis
}
</source>
this will include the class role::db::redis and look for role-related hiera configs in <tt>hieradata/role/codfw/db/redis.yaml</tt> and then in <tt>hieradata/role/common/db/redis.yaml</tt>, which may for example be:
<source lang="yaml">
cluster: redis
admin::groups:
  - redis-admins
</source>
 
Some machines, in particular miscellaneous servers, are "unique" and include an unique combination of classes; in that case, the best thing to do is '''not using''' the role keyword, and configure the variables at the host level in hiera:
 
<source lang="ruby">
node 'install2001.codfw.wmnet' {
      include standard
      include role::install-server
      include ganglia_new::collector
}
</source>
 
and then the hiera definition in <tt>hieradata/hosts/install2001.yaml</tt>
<source lang="yaml">
admin::groups:
  - mechanical-hamsters
</source>
 
== Coding Style ==
Please read the [http://docs.puppetlabs.com/guides/style_guide.html upstream style-guide]. And install [[Puppet_coding#install_puppet-lint|puppet-lint]].
===format===
Many existing manifests use two-spaces (as suggested in the style guide) instead of our 4 space indent standard; when working on existing code always follow the existing whitespace style of the file or module you are editing. Please do not mix cleanup changes with functional changes in a single patch.
====Spacing, Indentation, & Whitespace====
* Must use four-space soft tabs.
* Must not use literal tab characters.
* Must not contain trailing white space
* Must align fat comma arrows (=>) within blocks of attributes.
 
====Quoting====
* Must use single quotes unless interpolating variables.
* All variables should be enclosed in in braces ({}) when being interpolated in a string. [http://puppet-lint.com/checks/variables_not_enclosed/ like this]
* Variables standing by themselves should not be quoted.[http://puppet-lint.com/checks/only_variable_string/ like this]
* Must not quote booleans: '''<tt>true</tt>''' is ok, but not '''<tt>'true'</tt>''' or '''<tt>"true"</tt>'''
 
====Resources====
* Must single quote all resource names and their attribute, except ensure. (unless they contain a variable, of course).
* Ensure must always be the first attribute.
* Put a trailing comma after the final resource parameter.
* Again: Must align fat comma arrows (=>) within blocks of attributes.
* Don't group resources of the same type (a.k.a compression) :
do
        file { '/etc/default/exim4':
            require => Package['exim4-config'],
            owner  => 'root',
            group  => 'root',
            mode    => '0444',
            content => template('exim/exim4.default.erb'),
        }
        file { '/etc/exim4/aliases/':
            ensure  => directory,
            require => Package['exim4-config'],
            mode    => '0755',
            owner  => 'root',
            group  => 'root',
        }
don't do
        file { '/etc/default/exim4':
            require => Package['exim4-config'],
            owner  => 'root',
            group  => 'root',
            mode    => '0444',
            content => template('exim/exim4.default.erb');
      '/etc/exim4/aliases/':
            ensure  => directory,
            require => Package['exim4-config'],
            mode    => '0755',
            owner  => 'root',
            group  => 'root',
        }
* keep the resource name and the resource type on the same line. No need for extra indentation.
 
====Conditionals====
* Don't use selectors inside resources:
good:
    $file_mode = $::operatingsystem ? {
      debian => '0007',
      redhat => '0776',
      fedora => '0007',
    }
    file { '/tmp/readme.txt':
      content => "Hello World\n",
      mode    => $file_mode,
    }
bad:
    file { '/tmp/readme.txt':
      mode => $::operatingsystem ? {
        debian => '0777',
        redhat => '0776',
        fedora => '0007',
      }
    }
* Case statements should have default cases. [http://puppet-lint.com/checks/case_without_default/ like this].
 
====Classes====
All classes and resource type definitions must be in separate files in the manifests directory of their module.
* Do not nest classes.
* Ignore Inheritance as possible, puppet is not good at that. Also, inheritance will make your life harder when you need to use hiera - really, don't.
* Try not to use top-space variables, but if you do use them, scope them correctly:
$::operatingsystem
but not
$operatingsystem
* Do not use dashes in class names, preferably use alpha-betaic names only.
* In parameterized class and defined resource type declarations, parameters that are required should be listed before optional parameters. [http://puppet-lint.com/checks/parameter_order/ like this].
* It is in general better to avoid parameters that don't have a default; that will only make your life harder as you need to define that variable for every host that includes it.
 
====Including====
* One include per line.
* One class per include.
* Include only the class you need, not the entire scope.
 
== WMF Design conventions ==
* '''Always''' include the 'base' class for every node (note that ''standard'' includes ''base'' and should be used in most cases)
* For every service deployed, please use a <tt>system::role</tt> definition (defined in <tt>modules/system/manifests/role.pp</tt>) to indicate what a server is running. This will be put in the MOTD. As the definition name, you should normally use the relevant puppet class. For example:
system::role { "role::cache::bits": description => "bits Varnish cache server" }
* Files that are fully deployed by Puppet using the ''file'' type, should generally use a read-only file mode (i.e., '''0444''' or '''0555'''). This makes it more obvious that this file should not be modified, as Puppet will overwrite it anyway.
* For each service, create a nested class with the name <tt>''service''::monitoring</tt> (e.g. ''squid::monitoring'') which sets up any required (Nagios) monitoring configuration on the monitoring server.
* Any top-level class definitions should be documented with descriptive header, like this:
 
  # Mediawiki_singlnode: A one-step class for setting up a single-node MediaWiki install,
  #  running from a Git tree.
  #
  #  Roles can insert additional lines into LocalSettings.php via the
  #  $role_requires and $role_config_lines vars.
  #  etc.
 
Such descriptions are especially important for role classes.  Comments like these are used to generate our [http://doc.wikimedia.org/puppet/ online puppet documentation].
 
== Useful global variables ==
These are useful variables you can refer to from anywhere in the Puppet manifests. Most of these get defined in <tt>realm.pp</tt> or <tt>base.pp</tt>.
 
; <code>$::realm</code> : The "realm" the system belongs to. As of July 2013 we have the realms '''production''', '''fundraising''' and '''labs'''.
; <code>$::site</code> : Contains the 5-letter site name of the server, e.g. "[[pmtpa]]", "[[eqiad]]" or "[[esams]]".
 
== Before you submit a patch ==
 
=== Parser validation ===
 
You can syntax check your changes by
 
# puppet parser validate filename-here
 
=== Lint ===
You can locally install [http://puppet-lint.com/ puppet-lint] and use it to check your code before submitting, or enhance existing code by fixing puppet-lint errors/warnings.
[https://github.com/rodjek/puppet-lint puppet-lint on github]
==== install puppet-lint ====
===== on Debian/Ubuntu =====
apt-get install puppet-lint  [https://launchpad.net/ubuntu/+source/puppet-lint], [http://packages.debian.org/search?keywords=puppet-lint]
===== on Mac OS X =====
sudo gem install puppet-lint
 
===== generic (Ruby gem) =====
gem install puppet-lint
==== how to use ====
puppet-lint manifest.pp
or
puppet-lint --with-filename /etc/puppet/modules
==== common errors ====
 
===== tab character found on line .. =====
FIX: do not use tabs, use 4-space soft tabs
 
Have this in your vim config (.vimrc):
<pre>
set tabstop=4
set shiftwidth=4
set softtabstop=4
set smarttab
set expandtab
</pre>
 
or use something like this (if your local path is ./wmf/puppet/) to apply it to puppet files only.
 
<pre>
" Wikimedia style uses 4 spaces for indentation
autocmd BufRead */wmf/puppet/* set sw=4 ts=4 et
</pre>
 
open the file, :retab, :wq, done.  Make sure to review the resulting change carefully before submitting it.
 
Or put this in your emacs config (.emacs)
<pre>
;; Puppet config with 4 spaces
(setq puppet-indent-level 4)
(setq puppet-include-indent 4)
</pre>
 
===== double quoted string containing no variables =====
FIX: use single quotes (') for all strings unless there are variables to parse in it
===== unquoted file mode =====
FIX: always quote file modes with single quotes,like:  mode => '0750'
===== line has more than 80 characters =====
FIX: wrap your lines to be less than 80 chars, if you have to, there is \<newline>.
Vim can help when writing. Place this in your .vimrc
 
<pre>
set textwidth=80
</pre>
 
===== not in autoload module layout =====
FIX: turn your code into a puppet module ([http://docs.puppetlabs.com/puppet/2.7/reference/modules_fundamentals.html Module Fundamentals])
===== ensure found on line but it's not the first attribute =====
FIX: move your "ensure =>" to the top of the resource section. (don't forget to turn a ; into a , if it was the last attribute before)
===== unquoted resource title =====
FIX: quote all resource titles, single quotes
===== top-scope variable being used without an explicit namespace =====
FIX: use an explicit namespace in variable names ([http://docs.puppetlabs.com/guides/scope_and_puppet.html Scope and Puppet])
===== class defined inside a class =====
FIX: don't define classes inside classes
===== quoted boolean value =====
FIX: do NOT quote boolean values ( => true/ => false)
===== case statement without a default case =====
FIX: add a default case to your case statement
 
==== Ignoring lint warnings and errors ====
 
If you want you can always ignore specific warnings/errors by surrounding the relevant lines with a special "lint::ignore"-comment. For example, this would ignore "WARNING: top-scope variable being used without an explicit namespace" on line 54.
 
<pre>
53        # lint:ignore:variable_scope
54        default    => $fqdn
55        # lint:endignore
</pre>
 
You can get all the names of the separate checks with '''puppet-lint --help'''. More info is on http://puppet-lint.com/controlcomments/
 
==== Find out which warnings/errors are currently ignored ====
 
There are 2 parts to this. The first is to check the global .puppet-lint.rc file in the root of the puppet repo. You will see that the following 4 checks are currently ignored globally:
 
*--no-80-chars-check (This is about the lines over 80 chars, we are not planning to remove this exception)
*--no-autoloader_layout-check (This is about moving all remaining class out of manifests/role/ and https://phabricator.wikimedia.org/T119042 we want this fixed)
*--no-puppet-url_without_modules-check (Yes, we want this fixed)
*--no-documentation-check (https://phabricator.wikimedia.org/T127797)
 
The second part is checking for individual ignores, find these with a '''grep -r "lint:ignore" *''' in the root of the puppet repo. You can help by fixing and removing any of these remaining issues.
 
The tracking task for getting this to perfection is https://phabricator.wikimedia.org/T93645.
 
=== labs testing ===
 
Nontrivial puppet changes should be applies to a labs instance before being merged into production.  This can uncover some behaviors and code interactions that don't appear during individual file tests -- for example, puppet runs frequently fail due to duplicate resource definitions that aren't obvious to the naked eye.
 
To test a puppet patch:
 
1. Create a [[Help:Self-hosted_puppetmaster|self-hosted puppetmaster]]  instance.
 
2. Configure that instance so that it defines the class you're working on.  You can do this either via the 'configure instance' page or by editing /var/lib/git/operations/puppet/manifests/site.pp to contain something like this:
 
    node this-is-my-hostname {
        include class::I::am::working::on
    }
 
3. Run puppet a couple of times ('$ sudo puppetd -tv') until each subsequent puppet run is clean doesn't modify anything
 
4. Apply your patch to /var/lib/git/operations/puppet.  Do this by cherry-picking from gerrit or by rsyncing from a local working directory.
 
5. Run puppet again, and note the changes that this puppet run makes.  Does puppet succeed?  Are the changes what you expected?
 
== Manually Module testing ==
 
A relatively simple and crude testing way is
 
<pre>
puppet apply --noop --modulepath /path/to/modules <manifest>.pp
</pre>
 
Do note however that this might not work if you reference stuff outside of the module hierarchy
 
You can get around the missing module hierarchy problem by cloning a local copy of the puppet repo and symlinking in your new module directory.
 
eg.
<pre>
git clone --branch production https://git.wikimedia.org/git/operations/puppet.git
cd puppet/modules
ln -s /path/to/mymodule .
puppet apply --verbose --noop --modulepath=/home/${USER}/puppet/modules /path/to/mymodule/manifest/init.pp
</pre>
 
 
=== Unit Testing modules ===
 
==== Rake tests ====
Some modules have unit tests already written -- the other modules still need them!  Modules with tests have 'rakefile' in their top dir, and a subdir called 'spec'.
 
Modules imported from upstream typically have tests that run against other upstream modules -- we, however, seek to have tests pass when running only against our own repository.  In order to set that up you'll need to run
 
  $ rake spec
 
once in the top level directory to get things set up properly.  After that you can test individual modules by running
 
  $ rake spec_standalone
 
in specific module subdirs.
 
If you want to compare your results with the test results on our official testing box, check out this page:  https://integration.wikimedia.org/ci/job/test-puppet-rspec/
 
 
==== Custom tests ====
If you are testing a module it makes sense to group these simple tests in a tests/ directory in your modules hierarchy. Your tests can be as simple as
<pre>
#
 
include myclass
</pre>
 
in a file called myclass.pp in the tests directory.
 
or a lot more complex, calling parameterized classes and definitions.
 
All this can also be automated by including in the tests directory the following Makefile
 
<pre>
MANIFESTS=$(wildcard *.pp)
OBJS=$(MANIFESTS:.pp=.po)
TESTS_DIR=$(dir $(CURDIR))
MODULE_DIR=$(TESTS_DIR:/=)
MODULES_DIR=$(dir $(MODULE_DIR))
 
all: test
 
test: $(OBJS)
 
%.po: %.pp
puppet parser validate $<
puppet apply --noop --modulepath $(MODULES_DIR) $<
</pre>
 
and running make from the command line (assuming you have make installed)
 
Please note that --noop does not mean that no code will be executed. It means puppet wont change the state of any resource. So at least exec resources' conditionals as well puppet parser functions and facts will execute normally. So don't go around testing untrusted code.
 
= Roles =
 
A role is a particular kind of manifest that defines a specific job for a server. A role may pull in multiple other manifests, modules, etc. If you need to configure class variables specifically for this role, define one corresponding file in ''hieradata/mainrole/ROLE_NAME.yaml'' and define those variables there. We don't need global variables anymore.
 
In the ideal future, all manifests will either be roles or part of modules.  Top-level node definitions will /only/ include roles.  Any stand-alone manifests are anachronisms.  No manifest (including those in modules and the roles) should not make use of global variables.
 
Role classes should be named something like role::<function>[::subfunction].  They live in manifests/role, generally in files named after <function>. Sometimes a ::labs suffix is used, for example, modules/ldap/manifests/role/server.pp defines ldap::role::server::labs. But a ''::labs'' suffix shouldn't really be necessary now that we have hiera - just define a parameter for the role class for each functionality you may want or not want to activate, and use Hiera to configure them depending on the the realm or the site. Modules that can only be used in labs however should include a labs prefix, for example manifests/role/labsquarry.pp defines role::labs::quarry::web. In most cases, just defining class parameters for classes in modules per-environment should be enough.
 
= Puppet Modules =
 
There are currently two high level types of modules.  For most things, modules should not contain anything that is specific to the Wikimedia Foundation.  Non WMF specific modules could be useable an other puppet repository at any other organization. A WMF specific module is different: it may contain configurations specific to WMF (duh), but remember that it is still a module, so it must be useable on its own as well. Users of either type of module should be able able to use the module without editing anything inside of the module.  WMF specific modules will probably be higher level abstractions of services that use and depend on other modules, but they may not refer to anything inside of the top level manifests/ directory.  E.g. the 'applicationserver' module abstracts usages of apache, php and pybal to set up a WMF application server.
 
Often it will be difficult to choose between creating role classes and creating a WMF specific module.  There isn't a hard rule on this.  You should use your best judgement.  If role classes start to get overly complicated, you might consider creating a WMF specific module instead.
 
== 3rd party or upstream modules ==
There are so many great modules out there!  Why spend time writing your own?!
 
Well, for good reasons.  Puppet runs as root on the production nodes.  We can't import just any 3rd party module, as we can't be sure to trust them.  Not because they would do something malicious (although they might), but because they might do something stupid.
 
All 3rd party modules must be reviewed in the same manner that we review our own code before it goes to production.
 
== git submodules ==
Even so, since puppet modules are supposed to be their own projects, it is sometimes improper to maintain them as subdirectories inside of the operations/puppet repository.  This goes for 3rd party modules as well as non-WMF specific modules.  WMF specific modules can and probably should remain as subdirectories inside of operations/puppet.
 
We are starting to use git submodules to manage puppet modules.  Puppet modules must go through the same review process as anything in operations/puppet.
 
=== Adding a new puppet module as a git submodule ===
First up is adding a new puppet module.  'git submodule add' will modify the
.gitmodules file, and also take care of cloning the remote into the local
directory you specify.
 
  otto@localhost:~/puppet# git submodule add https://gerrit.wikimedia.org/r/p/operations/puppet/<my-module> modules/<my-module>
 
git status shows the modified .gitmodules file, as well as a new 'file' at
modules/<my-module>.  This new file is a pointer to a specific commit in the
<my-module> repository.
 
  otto@localhost:~/puppet# git status
  # On branch master
  # Changes to be committed:
  #  (use "git reset HEAD <file>..." to unstage)
  #
  # modified:  .gitmodules
  # new file:  modules/<my-module>
  #
 
Commit the changes and post them to gerrit for review.
 
  otto@localhost:~/puppet# git commit && git review
 
This will show up as a change in the operations/puppet repository.  This change will not show the actual code that is added, but instead, only show diffs with the SHA1s that the new submodule points at.  Once this change has been reviewed, approved, and merge, those with operations/puppet checked out will have to run
 
  git submodule update --init
 
to be sure that they get the changes required in their local working copies.  This is only really necessary if other users want to view the submodule's content locally.
 
=== Making changes to a submodule ===
 
'''You should never edit a submodule directly in the subdirectory a operations/puppet working copy.'''  If you want to make changes to a submodule, clone that submodule elsewhere directly.  Edit there and submit changes for review.
 
  git clone https://gerrit.wikimedia.org/r/p/operations/puppet/<my-module>
  cd <my-module>
  # edit stuff, push to gerrit for review.
  git commit && git review
 
Once your module change has been approved, you can update your operations/puppet working copy so that it points to the SHA1 you want it to.
 
  cd path/to/operations/puppet/modules/<my-module>
  git pull # or whatever you want to checkout your desired SHA1.
  cd ../..
  git commit .gitmodules && git review
 
This will push the update of the new SHA1 to operations/puppet for review.
 
= Miscellaneous =
 
== VIM guidelines ==
The following in ~/.vim/ftdetect/puppet.vim can help with a lot of formatting errors
 
<pre>
" detect puppet filetype
autocmd BufRead,BufNewFile *.pp set filetype=puppet
autocmd BufRead,BufNewFile *.pp setlocal tabstop=4 shiftwidth=4 softtabstop=4 expandtab textwidth=80 smarttab
</pre>
 
And for a proper syntax hightlighting the following can be done
 
<pre>
sudo aptitude install vim-puppet
mkdir -p ~/.vim/syntax
cp /usr/share/vim/addons/syntax/puppet.vim ~/.vim/syntax/
</pre>
 
And definitely have a look at https://github.com/scrooloose/syntastic which will report puppet errors directly in your buffer whenever you save the file (works for python/php etc as well).
 
Of course symlinks can be used or you can just install vim-addon-manager to manage plugins. vim-puppet provides ftplugin and indent plugin as well. Maybe there are worth the time, but it is up to each user to decide.
 
== Emacs guidelines ==
 
Syntax Highlighting
 
The puppet-el deb package can be used for emacs syntax highlighting, or the raw emacs libraries can be found
[https://github.com/puppetlabs/puppet-syntax-emacs here].
<pre>puppet-el - syntax highlighting for puppet manifests in emacs</pre>
 
The following two sections can be added to a .emacs file to help with 4 space indentions and trailing whitespace.
 
<pre>
;; Puppet config with 4 spaces
(setq puppet-indent-level 4)
(setq puppet-include-indent 4)
 
;; Remove Trailing Whitespace on Save
(add-hook 'before-save-hook 'delete-trailing-whitespace)
</pre>
 
== Puppet for Labs ==
 
There is currently only one puppet repository, and it is applied both to labs instances and production instances.  Classes may be added to the Operations/Puppet repository that are only intended for use on a labs instance.  The future is uncertain, though:  code is often reused, and labs services are sometimes promoted to production.  For that reason, any changes made to Operations/Puppet must be held to the same style and security standards as code that would be applied on a production service.
 
== Packages that use pip, gem, etc. ==
 
Other than mediawiki and related extensions, any software installed by puppet should be a Debian package and should come either from the WMF apt repo or from an official upstream Ubuntu repo.  Never use source-based packaging systems like pip or gem as these options haven't been properly evaluated and approved as secure by WMF Operations staff.
 
[[Category:Puppet]]

Latest revision as of 16:03, 29 June 2022