This post is part of the Open Source Cloud Computing series. For an Overview, please click on the Tag.
The Management Server
The Management Server is the entry point to the CloudStack Cloud. It manages all nodes and it exposes the API as well as the graphical user interface (GUI). Typically, the Management Server runs on a dedicated machine or virtual machine. The Management Server uses Tomcat and a MySQL Database for persistence. The Management Server also assigns public and private IP addresses and it also deals with the allocation of storage to the guests as virtual disks. CloudStack allows the management of snapshots, templates and ISO images, which is also provided by the Management Server.
The Cloud Infrastructure consists of several layers. The lowest level is the host itself, which is a node where virtual instances run on. Nodes usually get added to a cluster. A cluster contains several nodes and has a primary storage attached. Clusters are part of a Pod, which is typically a hardware rack including a layer-2 switch and a secondary storage. Pods are now part of a “Zone”, which represents a datacenter.
Zones are the largest entity in a CloudStack deployment. A zone normally represents a datacenter. Building various zones has the same benefits as building more datacenters: it enables replication and redundancy. CloudStack distinguishes between public and private zones. With this concept, it is possible to provide a public zone to all users and several private zones to specific users like the marketing or accounting department. When a new instance gets started, the user must select in which zone it should be launched. Clusters provide the ability to group similar nodes. They normally share the same or a very similar hardware, the same hypervisors, are in the same subnet and they share a primary storage. In large datacenters, clusters can be built for different hardware groups such as nodes with high memory, others with high CPU and or GPU-based Nodes. There are plenty of possibilities to distinguish between different hardware with the concept of clusters. ISCSI or NFS servers provide primary Storage and it is shared within a cluster. The primary storage stores all disk images of running virtual machines within the cluster. Secondary storage is associated with the zone and it’s purpose is to store templates, snapshots and ISO images.
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