119 lines
3.9 KiB
Markdown
119 lines
3.9 KiB
Markdown
[[!meta title="Propellor configuration for the Haskell newbie"]]
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Propellor's config file is written in Haskell, and
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[Haskell](http://www.haskell.org/) is invaluable to extend Propellor with
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your own custom properties. But you don't need to know about monads to
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configure Propellor!
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Let's take a quick tour of the `config.hs` file..
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[[!format haskell """
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-- | This is the main configuration file for Propellor, and is used to build
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-- the propellor program.
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"""]]
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So, `-- ` starts a comment in this file.
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[[!format haskell """
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import Propellor
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import Propellor.CmdLine
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import qualified Propellor.Property.File as File
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import qualified Propellor.Property.Apt as Apt
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import qualified Propellor.Property.User as User
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import qualified Propellor.Property.Cron as Cron
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"""]]
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This loads up Propellor's modules. You'll almost certainly want these;
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many more can be found in the [API documentation](http://hackage.haskell.org/package/propellor).
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[[!format haskell """
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main :: IO ()
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main = defaultMain hosts
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"""]]
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This config file *is* the Propellor program, and so it needs a little
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stub to go run itself. No need to ever change this part.
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`hosts` is the list of hosts that you configure, and it comes next:
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[[!format haskell """
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-- The hosts propellor knows about.
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-- Edit this to configure propellor!
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hosts :: [Host]
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hosts =
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[ host "mybox.example.com"
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& Apt.stdSourcesList Unstable
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, host "server.example.com"
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& Apt.stdSourcesList Stable
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& Apt.installed ["ssh"]
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]
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"""]]
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This defines a list of hosts, with two hosts in it.
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The configuration for the mybox host tells propellor to configure its
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`/etc/apt/sources.list` to use Debian `Unstable`.
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Of course you might want to change that to `Stable`.
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Each property of the host is prefixed with an "&" operator. This just makes
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a list of properties. Above, the first host has only 1 property, while
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the second host has 2 properties.
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Some other properties you may find in your config.hs, or want to add:
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[[!format haskell """
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& Apt.unattendedUpgrades
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& User.hasSomePassword "root"
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& "/etc/default/foodaemon" `File.containsLine` "ENABLED=yes"
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& Cron.runPropellor "30 * * * *"
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"""]]
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Some of these properties can be reverted -- this makes Propellor undo whatever
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effects they might have. For example, unattended upgrades can be scary, so
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maybe you turned that on, but want to disable it now. To do so, just change
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the "&" to a "!"
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[[!format haskell """
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! Apt.unattendedUpgrades
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"""]]
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Some properties cannot be reverted. Yet. It takes coding to implement
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revertability. If you try to revert a property that does not support
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reversion, propellor will **fail to compile**! This is a good thing..
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it avoids you getting confused or bad things happening.
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The error message when this happens might look a little scary. But if
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you read through it, it's remarkably precise about what and where the problem
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is.
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<pre>
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config.hs:30:19:
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Couldn't match expected type `RevertableProperty'
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with actual type `Property'
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In the return type of a call of `Apt.installed'
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In the second argument of `(!)', namely `Apt.installed ["ssh"]'
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In the first argument of `(&)', namely
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`host "mybox.example.com" & Apt.stdSourcesList Unstable
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& Apt.unattendedUpgrades
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! Apt.installed ["ssh"]'
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</pre>
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Similarly, if you make a typo in the config file, you'll probably get a long
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but informative error message.
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<pre>
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config.hs:27:19:
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Not in scope: `Apt.standardSourcesList'
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Perhaps you meant one of these:
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`Apt.stdSourcesList' (imported from Propellor.Property.Apt)
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...
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</pre>
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That's really all there is to configuring Propellor. Once you
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have a `config.hs` ready to try out, you can run `propellor --spin $host`
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on one of the hosts configured in it.
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See the [[README]] for a further quick start.
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(If you'd like to learn a little Haskell after all, check out
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[Learn You a Haskell for Great Good](http://learnyouahaskell.com/).)
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