how to install a cluster with propellor

Hello joey,

I would like to know your opinion, on the best way to install from scratch a cluster of at least 20 machines all identical, with propellor. I saw the FAI project, but I am wondering if this can be achieved with propellor only. The installation should be done remotly without human intervention except the propellor config and Indeed power on the cluster

Fred

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comment 1

Don't know that I have an answer to this question. I've never done that.

I think it breaks down into several independant questions, although due to lack of experience I could be missing some.

Initial installation

I'm working on getting propellor to be able to generate bootable disk images. http://joeyh.name/blog/entry/then_and_now/ Once that works, it might provide a way to generate images to install machines in a cluster. But, any method for installing the base system and propellor could work too, and there are probably many cluster-specific OS installation tools.

Expressing the cluster in a propellor config file

Propellor's config is a list of hosts, and defaultMain looks at the hostname to determine which host it is provisioning. A cluster might have many hosts that are very similar or identical, and you probably want it to be easy to add more.

So, you'll probably want a way to generate a Host from a HostName with the desired Properties you want nodes in the cluster to have:

clusterNode :: HostName -> Host
clusterNode hn = host hn
    & foo
    & bar

Then you could feed a list of hostnames to defaultMain to finish the config file:

main :: IO ()
main = defaultMain (map clusterNode hostnames)
  where
    hostnames = 
        [ "node1"
        , "node2"
        -- etc
        ]
    -- alternatively...
    -- hostnames = map (\n -> "node" ++ show n) [1..100]

Or, you could even look up the current hostname, and feed defaultMain a Host containing that hostname; so this single propellor configuration could be used on any number of hosts:

main = IO ()
main = do
    hn <- takeWhile (/= '\n') <$> readProcess "hostname" ["-f"]
    defaultMain [ clusterNode hn ]

Triggering propellor on nodes

When you change your propellor config.hs, you need a way to trigger the nodes to update. Propellor has a couple of different ways to do this; you could just use Propellor.Property.Cron.runPropellor to run it periodically from cron on all the nodes. (With a central git repository holding the propellor configuration, naturally.)

Or you could run propellor --spin against all the hosts in the cluster to push out a change. (It would be a nice enhancement to make propellor be able to --spin multiple hosts concurrently; there's nothing really preventing it but the output would be a mess.)

There's certianly room for improvement here. Also you'll probably want some monitoring, which propellor doesn't provide in itself, etc.

Comment by joey — Mon Aug 31 20:55:38 2015

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