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agent_certificate Puppet Module

This module allows to auto-renew Puppet Agent certificates

Table of Contents

  1. Description
  2. Workflow
  3. Security
  4. Usage
  5. Limitations

Description

Ever struggled with the renewal of your Puppet Agent certificates? Then this module might be what you're looking for. It has been designed to renew your certificates in an automated way.

Workflow

This module ships three additional facts:

  • agent_certificate_csr: a new CSR for the very same certificate name and private key. Shipped only when agent_certificate_expires is true
  • agent_certificate_expires: whether the current certificate reached 85% of it's lifetime
  • agent_certificate_path: Agent hostcert setting

During catalog compilation, a pending CSR will be validated. If accepted (read the Security section for details), the following steps take place on your compile master during (one single) catalog compile time:

  • in case the CA knows about the former certificate, it will be deleted (NOT revoked)
  • the new CSR will be sent to the CA
  • your CA server will be told to sign the new CSR
  • the new Certificate will be fetched
  • the Puppet catalog will contain file definitions backing up your old and creating the new certificate file on your Agent

The next Puppet Run should then take place with the renewed certificate.

Security

We cannot trust facts, so the following checks are applied at server side:

  • No CSRs are signed for Puppet runs without a trusted certificate (read: $::trusted['certname']).
  • CSRs that haven't been signed are rejected
  • CSRs with a subject not matching the nodes former certificate name are rejected
  • CSRs with subject alternative names are rejected in case the former certificate doesn't show the very same alternative names
  • Other CSR extensions are only allowed if the match the one in the former certificate (not yet, currently we reject requests with extensions)

Above checks involving the former certificate will result in the request being rejected in case the CA doesn't know the former certificate. CSRs with no subjectAlternativeName and no extension are processed even if the former certificate has been removed (but not revoked) on your CA server.

Usage

Usually all you have to do is to somehow assign this class:

include agent_certificate::auto_renew

Setting a custom TTL

You might want to tune the TTL, as automatic renewal allows for shorter TTLs:

class { 'agent_certificate::auto_renew':
  # TTL for renewed certificates
  # - MUST be Integer (seconds)
  # - defaults to the ca_ttl setting if not given
  # - this default is 86400 * 365 * 5 = 157680000
  # - example shows 90 days:
  expiration => 86400 * 90,
}

Advantage: you can keep your revocation lists smaller. We'd recommend to change the ca_ttl setting instead of using this feature. However, this parameter allows to have different TTLs for different types of host. No need to pollute your CRL (Certificate Revocation List) with lots of entries for short-lived containers or virtual machines.

Running in Dry Mode

Dry Mode allows to run simulation. Log will show notices telling you what WOULD happen when running in wet mode:

class { 'agent_certificate::auto_renew':
  dry_mode => true,
}

No Operation Mode

Don't let dry mode scare you, it is not a requirement for noop/test runs. This module also supports --noop. The challenge was that Facter doesn't care about --noop (there is no reason it should), and server-side Puppet functions are triggered run in noop mode too. So as experienced Puppet users might expect, this could have had undesired side-effects if we wouldn't care.

But we do, so be assured: --noop "just works" as expected.

Limitations

  • Agent Certificates only: this module replaces Agent Certificates, it doesn't care about expiring CA certificates
  • No support for Certificate Extenstions: Certificate extensions (like pp_*) are currently ignored, but we're working on this