(#236) agent_state_summary: Count nodes without report as unhealthy

It's possible that a Puppet Agent was stopped or disabled and all old
reports were garbage collected from PuppetDB. The node still exists in
PuppetDB, but when checking for a report the timestamp is null:

```
puppet query nodes[certname,report_timestamp]{}
```

```json
[
  {
    "certname": "pe.tim.local",
    "report_timestamp": "2024-09-30T13:21:17.042Z"
  },
  {
    "certname": "pe2.tim.local",
    "report_timestamp": null
  }
]
```

Previously we always assumed that `report_timestamp` has a valid
timestamp. With this patch we explicitly validate the timestamp and
count nodes withhout a timestamp as unhealthy.

Now with the fix:

```
puppet plan run pe_status_check::agent_state_summary --environment peadm log_healthy_nodes=true log_unhealthy_nodes=true
```

```json
{
    "responsive": [
        "pe.tim.local",
        "pe2.tim.local"
    ],
    "healthy_counter": 0,
    "total_counter": 2,
    "unhealthy_counter": 2,
    "noop": [],
    "unhealthy": [
        "pe2.tim.local",
        "pe.tim.local"
    ],
    "healthy": [],
    "changed": [
        "pe.tim.local"
    ],
    "no_report": [
        "pe.tim.local"
    ],
    "corrective_changes": [],
    "used_cached_catalog": [
        "pe2.tim.local"
    ],
    "unresponsive": [],
    "failed": []
}
```

README.md

@@ -168,6 +168,7 @@ The plan `pe_status_check::agent_state_summary` provides you a hash with all nod
   "failed": [ ],
   "changed": [ "student2.local" ],
   "unresponsive": [ "student3.local", "student4.local", "student1.local", "login.local" ],
+  "no_report": [ "newnode.with.report.local" ],
   "responsive": [ "pe.bastelfreak.local"],
   "unhealthy": [ "student2.local", "student3.local", "student4.local", "student1.local", "login.local" ],
   "unhealthy_counter": 5,
@@ -181,6 +182,7 @@ The plan `pe_status_check::agent_state_summary` provides you a hash with all nod
 * `failed`: The last catalog couldn't be compiled or catalog application raised an error
 * `changed`: A node reported a change
 * `unresponsive`: Last report is older than 30 minutes (can be configured via the `runinterval` parameter)
+* `no_report`: The node exists in PuppetDB but has no reports
 * `corrective_changes`: A node reported corrective changes
 * `used_cached_catalog`: The node didn't apply a new catalog but used a cached version
 * `unhealthy`: List of nodes that are in any of the above categories

plans/agent_state_summary.pp

@@ -16,10 +16,15 @@
   $nodes = puppetdb_query('nodes[certname,latest_report_noop,latest_report_corrective_change,cached_catalog_status,latest_report_status,report_timestamp]{}')
   $fqdns = $nodes.map |$node| { $node['certname'] }
 
-  # check if the last catalog is older than X minutes
+  # check if the node has a report
+  # `report_timestamp` will be undef, or null, if no report exists
+  $no_report_nodes = $nodes.filter |$node| { $node['report_timestamp'] =~ Undef }
+  $no_report = $no_report_nodes.map |$node| { $node['certname'] }
+
+  # check if the last report is older than X minutes, for all nodes that have a report
   $current_timestamp = Integer(Timestamp().strftime('%s'))
   $runinterval_seconds = $runinterval * 60
-  $unresponsive = $nodes.map |$node| {
+  $unresponsive = $no_report_nodes.map |$node| {
     $old_timestamp = Integer(Timestamp($node['report_timestamp']).strftime('%s'))
     if ($current_timestamp - $old_timestamp) >= $runinterval_seconds {
       $node['certname']
@@ -45,7 +50,7 @@
   $changed = $nodes.map |$node| { if ($node['latest_report_status'] == 'changed'){ $node['certname'] } }.filter |$node| { $node =~ NotUndef }
 
   # all nodes that aren't healthy in any form
-  $unhealthy = [$noop, $corrective_changes, $used_cached_catalog, $failed, $changed, $unresponsive].flatten.unique
+  $unhealthy = [$noop, $corrective_changes, $used_cached_catalog, $failed, $changed, $unresponsive, $no_report].flatten.unique
 
   # all healthy nodes
   $healthy = $fqdns - $unhealthy
@@ -58,6 +63,7 @@
       'failed'              => $failed,
       'changed'             => $changed,
       'unresponsive'        => $unresponsive,
+      'no_report'           => $no_report,
       'responsive'          => $responsive,
       'unhealthy'           => $unhealthy,
       'unhealthy_counter'   => $unhealthy.count,