Adding docs around the Subnet Available collector and analyzer

docs/source/host-collect-analyze/subnetAvailable.md

@@ -0,0 +1,81 @@
+---
+title: Subnet Available
+description:  Collect and analyze information about checking for an available (IPv4) subnet.
+---
+
+## Subnet Available Collector
+
+To check if there is an available (IPv4) subnet on a node, you can use the `subnetAvailable` collector. This is useful for Pod/Service CIDR ranges.
+
+This collector searches for overlap with the routing table of the node to help avoid conflicts.
+
+### Parameters
+
+In addition to the [shared collector properties](/collect/collectors/#shared-properties), the `subnetAvailable` collector accepts the following parameters:
+
+#### `CIDRRangeAlloc` (Required)
+The overarching subnet range to search for available CIDR blocks to use. The format must be `"x.x.x.x/y"`, with an IPv4 network and `y` being a CIDR mask between 1 and 32.
+
+#### `desiredCIDR` (Required)
+An integer between 1 and 32.
+
+Searches in `CIDRRangeAlloc` for an IP subnet of this CIDR block size.
+
+### Example Collector Definition
+
+```yaml
+apiVersion: troubleshoot.sh/v1beta2
+kind: HostPreflight
+metadata:
+  name: subnet-available
+spec:
+  collectors:
+    # would output yes/no depending if there is a /22 available in 10.0.0.0/8
+    - subnetAvailable:
+      CIDRRangeAlloc: "10.0.0.0/8"
+      desiredCIDR: 22
+```
+
+### Included Resources
+
+The results of the `subnetAvailable` collector are stored in the `host-collectors/subnetAvailable` directory of the support bundle.
+
+#### `[collector-name].json`
+
+If the `collectorName` field is not set, the file is named `result.json`.
+
+Example of the resulting JSON file:
+
+```json
+{
+  "CIDRRangeAlloc": "10.0.0.0/8",
+  "desiredCIDR": 22,
+  "status": "a-subnet-is-available"
+}
+```
+
+## Subnet Available Analyzer
+
+The `subnetAvailable` analyzer supports the following outcomes:
+
+- `a-subnet-is-available`: Indicates that a subnet of the `desiredCIDR` size is available within `CIDRRangeAlloc`.
+- `no-subnet-available`: Indicates that the entirety of `CIDRRangeAlloc` is exhausted by the node routing table, and that no subnets can be allocated of the `desiredCIDR` size.
+
+### Example Analyzer Definition
+
+```yaml
+apiVersion: troubleshoot.sh/v1beta2
+kind: HostPreflight
+metadata:
+  name: subnet-available
+spec:
+  analyzers:
+    - subnetAvailable:
+      outcomes:
+        - fail:
+          when: "no-subnet-available"
+          message: failed to find available subnet
+        - pass:
+          when: "a-subnet-is-available"
+          message: available /22 subnet found
+```