User Manual

148 | SMSEagle NXS-9700-3G | User’s Manual
Failover (HA-cluster) feature
"High-availability clusters (also known as HA clusters or fail over clusters) are groups of computers (...) that can be
reliably utilized with a minimum of down-time. They operate by using high availability software to harness
redundant computers in groups or clusters that provide continued service when system components fail. Without
clustering, if a server running a particular application crashes, the application will be unavailable until the crashed
server is fixed. HA clustering remedies this situation by detecting hardware/software faults, and immediately
restarting the application on another system or whole node without requiring administrative intervention, a process
known as failover." (source: Wikipedia)
SMSEagle NXS family has its own HA-cluster feature. For service to work you need at least 2 gateways
('aka' nodes). Our service monitors devices working in cluster and detects faults with following functions:
1. Apache2 WWW server
2. PostgreSQL database
3. SNMP agent
4. Modem software (Gammu-SMSD daemon)
5. Accessibility (response to ping) of whole node.
Every node in a cluster can have one of three states:
• Master: first healthy node which became available in a cluster, and is accessible through Virtual IP
• Backup: second healthy node in a cluster, ready and waiting for replacing Master when needed
• Fault: node with detected service fault
Basically devices (nodes) should see each other on the network. By default HA-nodes use 224.0.0.18 IP
address for VRRP (Virtual Router Redundancy Protocol) for communication between two nodes for health
check. If nodes are on the same network (same subnet & IP range) there is no need for any network
configuration. If two nodes are behind firewalls, make sure firewall is configured to accept multicast and
VRRP protocol (IP Protocol #112).