My participation in most projects has been as an employee of private companies and I can not make them public. Below I discuss some projects in freelancer time.
High-Availability Cluster in a virtual environment
Technology used: Centos, XEN, CONCA, iSCSI
The cluster infrastructure consists of four servers, three serves act as nodes (Node-1, Node-2 y Nodo-3) and the other server as Storage and the virtual part consists of 6 servers offering the following services:
Nagios : With Nagios monitor all our services (System and Networking)
WEBServer_1 : Hosts Web_1 Application
PDC (Samba -> LDAP) : Domain Controller, allows us to manage access to shared resources
PCBackup : Responsible for daily backups
DHCP/DNS : This virtual server provides local DHCP and DNS services
WEBServer_2 : Hosts Web_2 Application
The following picture shows the infrastructure of the Cluster
The iSCSI protocol (SCSI over IP) allows to store the virtual servers outside the nodes, specifically in the storage server and when a node fails, other nodes temporarily take control his virtual servers
Below is outlined the functioning of the cluster when a node fails. The figure shows the case when the Node-1 fails. The control software dectecta inactivity of this node and automatically migrates virtual servers WebServer_1 to Node-2 and virtual server Nagios to Node-3.
Once solved the problem with Node-1, the cluster detects that fallen node becomes operational and automatically migrates virtual servers Nagios and WebServer_1 to its original node (Node-1).