ZStack Resource Model

ZStack is essentially a configuration management system for resources in the Cloud. The following figure describes the resource model managed by ZStack, as shown in Figure 1.

ZStack mainly has the following resources:

Zone: the largest resource scope defined in ZStack. A zone is a logical group of resources, such as clusters, L2 networks, and primary storages.
Cluster: a logical group of analogy hosts (compute nodes).
Host: also known as a compute node, is a physical server that provides VM instances with compute, network, and storage resources.
Primary storage: a storage system that stores disk files, including root volumes, data volumes, root volume snapshots, data volume snapshots, and image caches, for VM instances. The types of primary storage include local storage, NFS, Shared Mount Point, SharedBlock, and Ceph.
Backup storage: a storage system that stores image templates. The types of backup storage include ImageStore, SFTP, and Ceph.
VXLAN pool: an underlay network in VXLAN. You can create multiple VXLAN overlay networks (VXLAN) in a VXLAN pool. The overlay networks can operate on the same underlay network device. The types of VXLAN pool include software SDN and hardware SDN.
L2 network: a layer 2 broadcast domain used for layer 2 isolation. Generally, L2 networks are identified by names of devices on the physical network. The types of L2 network include L2NoVlanNetwork, L2VlanNetwork, VxlanNetwork, and HardwareVxlanNetwork.
L3 network: a collection of network configurations for VM instances, including the IP range, gateway, DNS, and network services.
Instance offering: a specification of the VM instance CPU, memory, disk bandwidth, and network bandwidth.
Disk offering: a specification of a volume, which defines the size of a volume and how the volume will be created.
VM instance: a virtual machine instance running on a host. A VM instance has its own IP address to access public network and run application services. VM instances are core components of ZStack.
Image: an image template used by a VM instance or volume. Image template includes root volume images and data volume images. The types of root volume image include ISO and Image, while the type of data volume image is Image.
Root volume: the system disk where the VM instance operating system is installed.
Data volume: the data disk that provides additional storage for a VM instance.
Snapshot: a point-in-time capture of data in a disk. Snapshots are captured incrementally.
Network service module: a module for providing network services. This resource is hidden in the UI.
Network service: provides various network services for VM instances, including VPC firewall, security group, virtual IP (VIP), elastic IP (EIP), port forwarding, load balancing, IPsec tunnel, and flow monitoring.
VPC firewall: manages north-south traffic of the VPC network. You can manage the network access policy by configuring rule sets and rules.
Security group: provides L3 network firewall control over the VM instances, and controls TCP, UDP, and ICMP data packets for effective filtering. You can use a security group to effectively control specified VM instances on specified networks according to specified security rules.
Virtual router offering: an instance offering that defines the CPU, memory, virtual router (vRouter) image, management network, and public network used by a vRouter (including ordinary vRouter, VPC vRouter, and ARM vRouter).
Virtual router (vRouter): a custom Linux VM instance that provides network services such as DHCP, DNS, SNAT, route table, EIP, port forwarding, load balancing, and IPsec tunnel.
VPC vRouter: a router created directly from vRouter offering. VPC vRouter, which has a public network and a management network, is the core of VPC. VPC vRouter provides various network services, including DHCP, DNS, SNAT, route table, EIP, port forwarding, load balancing, IPsec tunnel, dynamic routing, multicast routing, VPC firewall, and Netflow.

The resource relationships in ZStack are as follows:

Parent-child: A resource can be the parent or child of another resource. For example, a host is the child resource of cluster, while a host is the parent resource of VM instance.
Sibling: Resources sharing the same parent resource are siblings. For example, clusters and L2 networks are sibling resources because all of them are child resources of zone.
Ancestor-descendant: A resource can be the lineal ancestor or lineal descendant of another resource. For example, a cluster is the ancestor resource of VM instance, while a host is a descendant resource of zone.
Friend: Resources that do not have the above three relationships but still need to cooperate with each other in some scenarios are friends. For example, primary storage and backup storage are friends. Also, zone and backup storage are friends.
Note: Relationship between primary storage and backup storage:
- When you create a VM instance, primary storage needs to download images of the VM instance as caches from backup storage.
- When you create an image, primary storage needs to copy the root volume to backup storage and save it as a template.

The following properties are common to almost all resources in ZStack:

UUID: the universally unique identifier. ZStack uses version 4 UUIDs to uniquely identify a resource.
Name: a human readable string that is used to identify resources. Names can be duplicated and are usually required.
Description: also known as a brief introduction that is used to briefly describe a resource. Description is usually optional.
Creation date: the date and time when a resource was created.
Last operation date: the date and time when a resource was updated last time.

Resources support full or partial Create, Read, Update, Delete (CRUD) operations.

Create: create or add a new resource.
Read: read or query information about a resource.
Update: update information about a resource.
Delete: delete a resource. Due to the cascade framework provided by ZStack, if a parent resource is deleted, its associated child resources and descendant resources will also be deleted.

Resource Pool

VM Instance

A VM instance is a virtual machine instance running on a host. A VM instance has its own IP address to access a public network and run application services. VM instances are core components of ZStack.

Volume

A volume provides storages for VM instances. A volume can either be a root volume or a data volume.

Root volume: A system disk where the VM instance operating system is installed.
Data volume: A data disk that provides additional storages for a VM instance.

Data volumes are mainly involved in the volume management.