Basic Pupet Managed Hiearchies

[Dennis Gearon]

Been burnnig up the keyboard and spewing packets to search for this answer, but haven't seen it.

From what I've read, there is only:
  A/ A Puppet Master
  B/ Infinite number of 'Agent' nodes.

Is this right?

Is there any other kinds of nodes?

Do Agent nodes ever control other nodes?

What happens when the puppet master gets overloaded, how do you cluster or use a 'super' master to divide the load?

Thanks for clearning this up for me :-)

[Jason Antman]

Agents never control other agents. Aside from supporting technology (PuppetDB, an ENC if you have one, a database to back PuppetDB), yeah, a master and N agents is the gist of it.

There are some docs online (see specifically the "Tuning and Scaling" section of the Puppet Documentation Index, https://docs.puppetlabs.com/puppet/#tuning-and-scaling ) about scaling, and a search of the mailing list archives (as well as Google - there have been quite a few blog posts on this) should help turn up other options and experiences.

Off the top of my head, I believe there are generally two paradigms used: either clustering/HA for your masters, generally load-balanced from what I gather, or (what I do) splitting up agents between different masters (by location, or network, or dev/test/prod). My current infrastructure is made up of ~450 nodes which are served by three masters - dev, test/QA and prod. We run every 30 minutes, via mcollective with a set concurrency. The masters are VMs, running on the same physical hosts as PuppetDB and its PostgreSQL instance, so I'm quite confident that I could scale each one to a few thousand nodes before I have to worry about overloading one host. In addition, since we split dev, test/QA and prod masters, we can deploy module changes (and puppet/puppetdb/etc. upgrades) to the dev environment, validate there, promote to test/QA, validate there, and then promote to prod.

-Jason

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[Dennis Gearon]

Thanks Jason. If I ever get to 1000 nodes, then I guess I'll have something to worry about, then. LOL! One final question.

An 'agent' is really a managed server instance, not a Puppet worker managing something else, (as the word 'Agent' would suggest). So really, Agents only apply catalogs to themselves, right?

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[Jason Antman]

With a very small edge-case asterisk (the puppet Device support, which I've never used), yes. The agent is a piece of software that runs (as a daemon, via cron, manually, or via some other scheduling mechanism like mcollective) on a host ("node" in Puppet nomenclature) and applies catalogs to that one node.

There's a good introduction to this at https://docs.puppetlabs.com/learning/agent_master_basic.html - I'd also encourage you to look through the rest of the Learning Puppet section on docs.puppetlabs.com.

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[Dennis Gearon]

Thanks again, Jason. I'll spin some up today and run through some more docs, tutorias.

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