278 lines
8.6 KiB
ReStructuredText
278 lines
8.6 KiB
ReStructuredText
Best practice
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=============
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Practices used in real environments
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Passwordless connections
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------------------------
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It is recommended to run cdist with public key authentication.
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This requires a private/public key pair and the entry
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"PermitRootLogin without-password" in the sshd server.
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See sshd_config(5) and ssh-keygen(1).
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Speeding up ssh connections
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---------------------------
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When connecting to a new host, the initial delay with ssh connections
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is pretty big. As cdist makes many connections to each host successive
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connections can be sped up by "sharing of multiple sessions over a single
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network connection" (quote from ssh_config(5)). This is also called "connection
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multiplexing".
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Cdist implements this since v4.0.0 by executing ssh with the appropriate
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options (`-o ControlMaster=auto -o ControlPath=/tmp/<tmpdir>/s -o
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ControlPersist=2h`).
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Note that the sshd_config on the server can configure the maximum number of
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parallel multiplexed connections this with `MaxSessions N` (N defaults to 10
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for OpenSSH v7.4).
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Speeding up shell execution
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----------------------------
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On the source host, ensure that /bin/sh is *not* bash: bash is quite slow for
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script execution. Instead, you could use dash after installing it::
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ln -sf /bin/dash /bin/sh
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Multi master or environment setups
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----------------------------------
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If you plan to distribute cdist among servers or use different
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environments, you can do so easily with the included version
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control git. For instance if you plan to use the typical three
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environments production, integration and development, you can
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realise this with git branches::
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# Go to cdist checkout
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cd /path/to/cdist
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# Create branches
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git branch development
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git branch integration
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git branch production
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# Make use of a branch, for instance production
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git checkout production
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Similar if you want to have cdist checked out at multiple machines,
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you can clone it multiple times::
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machine-a % git clone git://your-git-server/cdist
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machine-b % git clone git://your-git-server/cdist
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Separating work by groups
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-------------------------
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If you are working with different groups on one cdist-configuration,
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you can delegate to other manifests and have the groups edit only
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their manifests. You can use the following snippet in
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**conf/manifests/init**::
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# Include other groups
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sh -e "$__manifest/systems"
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sh -e "$__manifest/cbrg"
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Maintaining multiple configurations
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-----------------------------------
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When you need to manage multiple sites with cdist, like company_a, company_b
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and private for instance, you can easily use git for this purpose.
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Including a possible common base that is reused across the different sites::
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# create branches
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git branch company_a company_b common private
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# make stuff for company a
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git checkout company_a
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# work, commit, etc.
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# make stuff for company b
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git checkout company_b
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# work, commit, etc.
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# make stuff relevant for all sites
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git checkout common
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# work, commit, etc.
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# change to private and include latest common stuff
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git checkout private
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git merge common
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The following **.git/config** is taken from a real world scenario::
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# Track upstream, merge from time to time
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[remote "upstream"]
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url = git://git.schottelius.org/cdist
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fetch = +refs/heads/*:refs/remotes/upstream/*
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# Same as upstream, but works when being offline
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[remote "local"]
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fetch = +refs/heads/*:refs/remotes/local/*
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url = /home/users/nico/p/cdist
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# Remote containing various ETH internal branches
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[remote "eth"]
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url = sans.ethz.ch:/home/services/sans/git/cdist-eth
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fetch = +refs/heads/*:refs/remotes/eth/*
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# Public remote that contains my private changes to cdist upstream
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[remote "nico"]
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url = git.schottelius.org:/home/services/git/cdist-nico
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fetch = +refs/heads/*:refs/remotes/nico/*
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# The "nico" branch will be synced with the remote nico, branch master
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[branch "nico"]
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remote = nico
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merge = refs/heads/master
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# ETH stable contains rock solid configurations used in various places
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[branch "eth-stable"]
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remote = eth
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merge = refs/heads/stable
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Have a look at git-remote(1) to adjust the remote configuration, which allows
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Multiple developers with different trust
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----------------------------------------
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If you are working in an environment that requires different people to
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work on the same configuration, but having different privileges, you can
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implement this scenario with a gateway host and sudo:
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- Create a dedicated user (for instance **cdist**)
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- Setup the ssh-pubkey for this user that has the right to configure all hosts
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- Create a wrapper to update the cdist configuration in ~cdist/cdist
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- Allow every developer to execute this script via sudo as the user cdist
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- Allow run of cdist as user cdist on specific hosts on a per user/group basis.
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- f.i. nico ALL=(ALL) NOPASSWD: /home/cdist/bin/cdist config hostabc
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For more details consult sudoers(5)
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Templating
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----------
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* create directory files/ in your type (convention)
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* create the template as an executable file like files/basic.conf.sh, it will output text using shell variables for the values
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.. code-block:: sh
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#!/bin/sh
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# in the template, use cat << eof (here document) to output the text
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# and use standard shell variables in the template
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# output everything in the template script to stdout
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cat << EOF
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server {
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listen 80;
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server_name $SERVERNAME;
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root $ROOT;
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access_log /var/log/nginx/$SERVERNAME_access.log
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error_log /var/log/nginx/$SERVERNAME_error.log
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}
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EOF
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* in the manifest, export the relevant variables and add the following lines to your manifest:
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.. code-block:: console
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# export variables needed for the template
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export SERVERNAME='test"
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export ROOT='/var/www/test'
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# render the template
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mkdir -p "$__object/files"
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"$__type/files/basic.conf.sh" > "$__object/files/basic.conf"
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# send the rendered template
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__file /etc/nginx/sites-available/test.conf \
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--state present
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--source "$__object/files/basic.conf"
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Testing a new type
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------------------
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If you want to test a new type on a node, you can tell cdist to only use an
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object of this type: Use the '--initial-manifest' parameter
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with - (stdin) as argument and feed object into stdin
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of cdist:
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.. code-block:: sh
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# Singleton type without parameter
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echo __ungleich_munin_server | cdist --initial-manifest - munin.panter.ch
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# Singleton type with parameter
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echo __ungleich_munin_node --allow 1.2.3.4 | \
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cdist --initial-manifest - rails-19.panter.ch
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# Normal type
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echo __file /tmp/stdintest --mode 0644 | \
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cdist --initial-manifest - cdist-dev-01.ungleich.ch
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Other content in cdist repository
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---------------------------------
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Usually the cdist repository contains all configuration
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items. Sometimes you may have additional resources that
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you would like to store in your central configuration
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repository (like password files from KeepassX,
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Libreoffice diagrams, etc.).
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It is recommended to use a subfolder named "non-cdist"
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in the repository for such content: It allows you to
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easily distinguish what is used by cdist and what is not
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and also to store all important files in one
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repository.
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Notes on CDIST_ORDER_DEPENDENCY
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-------------------------------
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With CDIST_ORDER_DEPENDENCY all types are executed in the order in which they
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are created in the manifest. The current created object automatically depends
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on the previously created object.
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It essentially helps you to build up blocks of code that build upon each other
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(like first creating the directory xyz than the file below the directory).
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This can be helpful, but one must be aware of its side effects.
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CDIST_ORDER_DEPENDENCY kills parallelization
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Suppose you have defined CDIST_ORDER_DEPENDENCY and then, among other things,
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you specify creation of three, by nature independent, files.
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**init**
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.. code-block:: sh
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CDIST_ORDER_DEPENDENCY=1
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export CDIST_ORDER_DEPENDENCY
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...
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__file /tmp/file1
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__file /tmp/file2
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__file /tmp/file3
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...
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Due to defined CDIST_ORDER_DEPENDENCY cdist will execute them in specified order.
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It is better to use CDIST_ORDER_DEPENDENCY in well defined blocks:
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**init**
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.. code-block:: sh
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CDIST_ORDER_DEPENDENCY=1
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export CDIST_ORDER_DEPENDENCY
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...
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unset CDIST_ORDER_DEPENDENCY
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__file /tmp/file1
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__file /tmp/file2
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__file /tmp/file3
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CDIST_ORDER_DEPENDENCY=1
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export CDIST_ORDER_DEPENDENCY
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...
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unset CDIST_ORDER_DEPENDENCY
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