Add profiles::puppet::migrate: repoint VM agents onto puppet-on-k8s (#493)

## Why

Migrate the VM puppet agents off the legacy VM puppetmasters onto the new puppet-on-kubernetes servers, one wave at a time and reversible without re-enrolment.

Changing `server`/`ca_server` alone is insufficient: each agent's ssldir holds a client certificate signed by the **old** CA, which the new k8s CA neither trusts nor recognises. Migrated nodes switch to a **fresh ssldir**, so the agent generates a new key + CSR on its next run (autosigned immediately by the k8s CA, which runs `autosign = true`), pulls its catalog from the new compilers, and leaves the old CA-signed creds intact on disk for rollback.

The reconfiguration catalog is compiled by the **old** server (the node still points there when it applies the change). `profiles::puppet::client` rewrites `puppet.conf` with the new endpoints + ssldir and notifies `Service['puppet']`, so the very next agent run lands on k8s.

**Single-boolean design (reworked):** cutover is now driven by one hiera key. `profiles::puppet::migrate` ships wired into `profiles::base` with `enabled => false`, so every node evaluates it but nothing changes until the boolean is flipped. `profiles::puppet::client` includes migrate and folds the migrate endpoints into the effective values it renders. Flip `profiles::puppet::migrate::enabled: true` at any hiera layer (node/role/common) to migrate a target -- no other keys required.

## Changes

- `profiles::base` (`site/profiles/manifests/base.pp`): `include profiles::puppet::migrate` alongside the other puppet profiles (ships disabled).
- `profiles::puppet::migrate` (`site/profiles/manifests/puppet/migrate.pp`): unchanged params (`enabled=false`, `new_server`, `new_ca_server`, `new_ssldir`); when enabled and the node is not a puppetmaster it owns the fresh ssldir directory. Class-header runbook rewritten for the single-boolean flow. No longer opt-in via `hiera_include`.
- `profiles::puppet::client` (`site/profiles/manifests/puppet/client.pp`): `include profiles::puppet::migrate` and compute `$effective_server` / `$effective_ca_server` / `$effective_report_server` / `$effective_ssldir`, feeding those to the template. Keeps the existing optional `$ssldir` / `$report_server` params as manual overrides.
- `puppet.conf.erb`: render from the `@effective_*` vars.

## Precedence

- **ssldir / report_server** (`Optional`, default `undef`): explicit `profiles::puppet::client::ssldir` / `::report_server` in hiera wins; else the migrate-derived value when `enabled`; else the legacy default (ssldir omitted -> puppet default; report_server -> effective server).
- **server / ca_server** (`String`, no undef sentinel): the migrate endpoint wins while `enabled => true`; otherwise the client param (legacy default unless set explicitly). To pin a bespoke server, leave `enabled => false` for that target and set `profiles::puppet::client::server` directly.
- No include cycle: migrate.pp never references client.pp; its guard uses `$facts['enc_role']`.

## Runbook

- **Canary (one node)** -> `hieradata/nodes/<certname>.yaml`: `profiles::puppet::migrate::enabled: true`
- **Wave (a role)** -> `hieradata/roles/<t1>/<t2>[/<t3>].yaml`: `profiles::puppet::migrate::enabled: true`
- **Estate flip** -> `hieradata/common.yaml`: `profiles::puppet::migrate::enabled: true`
- **Rollback** -> remove the key (or set `false`) at that layer; next run rewrites puppet.conf back to the legacy server + legacy ssldir (original CA-signed cert intact).
- The k8s endpoints (`new_server` / `new_ca_server` / `new_ssldir`) are `profiles::puppet::migrate` param defaults; override them in hiera if the k8s names change.

## Verification

- Render comparison: unmigrated node renders a **byte-identical** `puppet.conf` to `develop` (diff empty). Migrated render (only `enabled: true`) emits `server`/`ca_server`/`report_server` = k8s endpoints and `ssldir = /etc/puppetlabs/puppet/ssl-k8s`.
- `puppet-lint` (repo args `--no-80chars-check --no-documentation-check --no-puppet_url_without_modules-check --fail-on-warnings`): clean on all 3 manifests.
- `puppet parser validate`: OK. ERB syntax: OK. Repo pre-commit hooks (erb-validate, puppet-lint, puppet-validate): all Passed.

Reviewed-on: #493
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

site/profiles/manifests/puppet/migrate.pp

@@ -0,0 +1,87 @@
+# Class: profiles::puppet::migrate
+#
+# Repoints a VM puppet agent from the legacy VM puppetmasters onto the new
+# puppet-on-kubernetes servers.
+#
+# The agent's existing ssldir holds a client certificate signed by the OLD CA;
+# the new k8s CA will neither trust that cert nor recognise the agent. Rather
+# than revoke/clean the old creds (which would burn the rollback path), this
+# class switches the agent to a FRESH ssldir. On the next run the agent finds
+# an empty ssldir, generates a new key + CSR, submits it to the new CA
+# (autosign = true on the k8s side signs it immediately), and then pulls its
+# catalog from the new compilers. The OLD ssldir is left untouched on disk, so
+# reverting the hiera below restores the node to the legacy masters with no
+# re-enrolment.
+#
+# The catalog that performs the switch is compiled by the OLD server (the node
+# still points at it when it applies this change). profiles::puppet::client
+# rewrites puppet.conf with the new server / ca_server / report_server / ssldir
+# and notifies Service['puppet'], so the very next agent run lands on k8s.
+#
+# NOTE: this is deliberately hiera-driven per node/role so waves can be rolled
+# out and rolled back one target at a time. The class only manages the fresh
+# ssldir; the actual puppet.conf changes ride on profiles::puppet::client's
+# existing template. client.pp `include`s this class and, when enabled, folds
+# new_server / new_ca_server / new_ssldir into the effective server /
+# ca_server / report_server / ssldir it renders. Do NOT add a second File
+# resource for puppet.conf here -- client.pp already owns it.
+#
+# == Wiring (single boolean)
+#
+# This class ships wired into profiles::base with enabled => false, so every
+# node evaluates it but nothing changes until the boolean is flipped. Because
+# client.pp includes it and reads its params, setting the ONE key below at any
+# hiera layer repoints a target -- no client.pp param overrides needed.
+#
+# The endpoints (new_server / new_ca_server / new_ssldir) are param defaults
+# on this class; override them in hiera too if the k8s names ever change.
+#
+# --- Canary: one node -> hieradata/nodes/<certname>.yaml -------------------
+#   profiles::puppet::migrate::enabled: true
+# ---------------------------------------------------------------------------
+#
+# --- Wave: a whole role -> hieradata/roles/<t1>/<t2>[/<t3>].yaml -----------
+#   profiles::puppet::migrate::enabled: true
+# ---------------------------------------------------------------------------
+#
+# --- Estate flip -> hieradata/common.yaml (retires the legacy masters) -----
+#   profiles::puppet::migrate::enabled: true
+# ---------------------------------------------------------------------------
+#
+# Manual override: profiles::puppet::client::ssldir and ::report_server are
+# Optional and, when set explicitly in hiera, win over the migrate-derived
+# value. server / ca_server have no undef sentinel, so while enabled => true
+# the migrate endpoints win; to point a target at a bespoke server leave
+# enabled => false for it and set profiles::puppet::client::server directly.
+#
+# == Rollback (per target)
+#
+# Remove the profiles::puppet::migrate::enabled key (or set it back to false)
+# at the node/role/common layer. The next run rewrites puppet.conf back to the
+# legacy server + legacy ssldir, which still contains the original CA-signed
+# cert, and the node is back on the VM masters.
+#
+# site/profiles/manifests/puppet/migrate.pp
+class profiles::puppet::migrate (
+  Boolean $enabled                          = false,
+  String $new_server                        = 'puppet.k8s.syd1.au.unkin.net',
+  String $new_ca_server                     = 'puppetca.k8s.syd1.au.unkin.net',
+  Stdlib::Absolutepath $new_ssldir          = '/etc/puppetlabs/puppet/ssl-k8s',
+) {
+
+  # never touch the puppet masters themselves (same guard as client.pp)
+  if $enabled and $facts['enc_role'] != 'roles::infra::puppet::master' {
+
+    # Ensure the fresh ssldir exists with agent-correct ownership/perms. The
+    # puppet agent will create it on demand, but pre-creating it keeps the very
+    # first post-switch run from racing directory creation and makes the
+    # migration state auditable. Contents (keys, certs, crl) are populated by
+    # the agent against the new CA -- we only own the directory itself.
+    file { $new_ssldir:
+      ensure => 'directory',
+      owner  => 'root',
+      group  => 'root',
+      mode   => '0771',
+    }
+  }
+}