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collections/documentation/developers/internals/zos/internals/vmd/readme.md

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+<h1>VMD Module</h1>
+
+<h2> Table of Contents </h2>
+
+- [ZBus](#zbus)
+- [Home Directory](#home-directory)
+- [Introduction](#introduction)
+	- [zinit unit](#zinit-unit)
+- [Interface](#interface)
+
+***
+
+## ZBus
+
+Storage module is available on zbus over the following channel
+
+| module | object | version |
+|--------|--------|---------|
+| vmd|[vmd](#interface)| 0.0.1|
+
+## Home Directory
+
+contd keeps some data in the following locations
+| directory | path|
+|----|---|
+| root| `/var/cache/modules/containerd`|
+
+## Introduction
+
+The vmd module, manages all virtual machines processes, it provide the interface to, create, inspect, and delete virtual machines. It also monitor the vms to make sure they are re-spawned if crashed. Internally it uses `cloud-hypervisor` to start the Vm processes.
+
+It also provide the interface to configure VM logs streamers.
+
+### zinit unit
+
+`contd` must run after containerd is running, and the node boot process is complete. Since it doesn't keep state, no dependency on `stroaged` is needed
+
+```yaml
+exec: vmd --broker unix:///var/run/redis.sock
+after:
+  - boot
+  - networkd
+```
+
+## Interface
+
+```go
+
+// VMModule defines the virtual machine module interface
+type VMModule interface {
+	Run(vm VM) error
+	Inspect(name string) (VMInfo, error)
+	Delete(name string) error
+	Exists(name string) bool
+	Logs(name string) (string, error)
+	List() ([]string, error)
+	Metrics() (MachineMetrics, error)
+
+	// VM Log streams
+
+	// StreamCreate creates a stream for vm `name`
+	StreamCreate(name string, stream Stream) error
+	// delete stream by stream id.
+	StreamDelete(id string) error
+}
+```