# Run Strategies

## Overview

VirtualMachines have a `Running` setting that determines whether or not there should be a guest running or not. Because KubeVirt will always immediately restart a VirtualMachineInstance for VirtualMachines with `spec.running: true`, a simple boolean is not always enough to fully describe desired behavior. For instance, there are cases when a user would like the ability to shut down a guest from inside the virtual machine. With `spec.running: true`, KubeVirt would immediately restart the VirtualMachineInstance.

## RunStrategy

To allow for greater variation of user states, the `RunStrategy` field has been introduced. This is mutually exclusive with `Running` as they have somewhat overlapping conditions. There are currently four RunStrategies defined:

* Always: A VirtualMachineInstance will always be present. If the VirtualMachineInstance crashed, a new one will be spawned. This is the same behavior as `spec.running: true`.
* RerunOnFailure: A VirtualMachineInstance will be respawned if the previous instance failed in an error state. It will not be re-created if the guest stopped successfully (e.g. shut down from inside guest).
* Manual: The presence of a VirtualMachineInstance or lack thereof is controlled exclusively by the start/stop/restart VirtualMachine subresource endpoints.
* Halted: No VirtualMachineInstance will be present. If a guest is already running, it will be stopped. This is the same behavior as `spec.running: false`.

_Note_: RunStrategy and Running are mutually exclusive, because they can be contradictory. The API server will reject VirtualMachine resources that define both.

### Virtctl

The `start`, `stop` and `restart` methods of virtctl will invoke their respective subresources of VirtualMachines. This can have an effect on the runStrategy of the VirtualMachine as below:

| RunStrategy        | start    | stop     | restart          |
| ------------------ | -------- | -------- | ---------------- |
| **Always**         | `-`      | `Halted` | `Always`         |
| **RerunOnFailure** | `-`      | `Halted` | `RerunOnFailure` |
| **Manual**         | `Manual` | `Manual` | `Manual`         |
| **Halted**         | `Always` | `-`      | `-`              |

Table entries marked with `-` don't make sense, so won't have an effect on RunStrategy.

## RunStrategy Examples

### Always

An example usage of the Always RunStrategy.

```
apiVersion: kubevirt.io/v1alpha3
kind: VirtualMachine
metadata:
  labels:
    kubevirt.io/vm: vm-cirros
  name: vm-cirros
spec:
  runStrategy: Always
  template:
    metadata:
      labels:
        kubevirt.io/vm: vm-cirros
    spec:
      domain:
        devices:
          disks:
          - disk:
              bus: virtio
            name: containerdisk
      terminationGracePeriodSeconds: 0
      volumes:
      - containerDisk:
          image: kubevirt/cirros-container-disk-demo:latest
        name: containerdisk
```
