Load Balancing

It is possible to add load balanced (LB) Web and mail clusters to Parallels H-Sphere. Load balancing implies balancing server traffic amongst multiple computers (LB cluster) which Parallels H-Sphere regards and operates with as a single server.

Load balanced cluster solution in Parallels H-Sphere requires 4 or more physical servers:

• Load Balancer: any solution like Cytrix® NetScaler (http://www.citrix.com/English/ps2/products/subfeature.asp?contentID=22314) for balancing traffic across the web/mail servers. Load Balancer directs traffic to another server if the first one is currently overloaded. It can also allow the service to continue even if one of the servers is down.
• One master and one or more slave servers form a load balanced Web/mail cluster. All these servers are being added to Parallels H-Sphere as physical servers, with all related packages installed, but Parallels H-Sphere logical servers are created only on master servers, and Parallels H-Sphere operates with load balanced cluster only via master server.
• NAS (Network Attached Storage): shared storage for master and slave servers. NAS is a highly reliable server with enough space for storing data. Web/mail content directories are mounted to the NAS where the content is actually stored. Web and mail servers can jointly use one NAS or have their own NAS for Web and for mail.

Figure 1: Simple Load Balanced system with one Web cluster:

Figure 2: More complex Load Balanced system with two mail and two web clusters:

Load Balancers

You need to purchase, install and configure any load balancer solution, for example, Cytrix® NetScaler (http://www.citrix.com/English/ps2/products/subfeature.asp?contentID=22314).
This task is beyond the scope of Parallels H-Sphere documentation.

Supported NAS

The following file storage systems are supported by Parallels H-Sphere:

Note: All Parallels H-Sphere customers will be recommended to choose shared Linux NFS as the most simple and reliable solution.

Load Balanced Cluster

Loab balanced cluster consists of one master and one or more slave servers regarded by Parallels H-Sphere as a single server.

• Master and slave servers are added to Parallels H-Sphere as physical servers.
• Master-slave relations between these servers are set in admin CP.
• Only master server is added as Web/mail logical server to Parallels H-Sphere. CP communicates only with master server.
• Requests are passed to external IPs routed by the load balancer. Load balancer distributes requests evenly across the master and slave servers (internal IPs corresponding to external IP). For this purpose, NAT must be properly configured on load balanced cluster servers.
• Master and slave server share the same Parallels H-Sphere related directories where all user content, scripts, and the majority of Parallels H-Sphere related binaries are located. These directories are actually stored on the NAS and mounted from master and slave servers via NFS.
• Along with shared storage, master and slave servers have their own unique IP-specific logs and configs which are synchronized by special cron scripts run on these servers.

See load balanced cluster scheme with generic Linux NFS shared storage.