Document persist_rootfs option (#2236)

* Document rootfs persistence

* Update reference/configuration.html.markerb

Co-authored-by: Kristin Martin <[email protected]>

* Update machines/api/machines-resource.html.markerb

Co-authored-by: Kristin Martin <[email protected]>

---------

Co-authored-by: Kristin Martin <[email protected]>

Author: dangra

machines/api/machines-resource.html.markerb

@@ -1182,8 +1182,9 @@ Properties of the `config` object for Machine configuration. See [Machine proper
   - `host_dedication_id`: The ID of the host dedication (group of dedicated hosts) on which to create this Machine. (beta)
   - `cpus`: int (nil) - The number of CPU cores this Machine should occupy when it runs. (default `1`)
   - `gpus`: int (nil) - The number of GPU cores this Machine should occupy when it runs. (default `1`)
-  - `kernel_args`: Optional array of strings. Arguments passed to the kernel.
   - `memory_mb`: int (nil) - Memory in megabytes as multiples of 256 (default `256`)
+  - `kernel_args`: Optional array of strings. Arguments passed to the kernel.
+  - `persist_rootfs`: string (nil) - The root filesystem will be persisted across restarts and updates. Possible values are `never` (default), `restart`, and `always`.
 
 ---
 

reference/configuration.html.markerb

@@ -840,6 +840,7 @@ All keys are optional and `size` has lower precedence than all other keys.
   gpu_kind = "a100-pcie-40gb"
   kernel_args = "no-hlt=true"
   host_dedication_id = "customer-id"
+  persist_rootfs = "never"
   processes = ["app"]
 ```
 
@@ -881,6 +882,14 @@ Additional kernel parameters provided to the kernel when booting the VM.
 
 In the case of having a dedicated host, this is the value to set so Machines are launched on dedicated hardware.
 
+### persist_rootfs
+
+The persistence of the root filesystem across restarts and updates. Valid values are `never` (default), `restart`, and `always`.
+
+- `never`: The root filesystem is ephemeral and will not be persisted across restarts or updates.
+- `restart`: The root filesystem is persisted across restarts, but not across updates.
+- `always`: The root filesystem is persisted across restarts and updates.
+
 ### `processes`
 
 Optionally, you can specify a list of [processes](#the-processes-section) to limit by process group. You can even specify two different `[[vm]]` sections to have different compute requirements per process group. Note the need to use double brackets if there are multiple `[[vm]]` sections defined.