High Availability Overview

High Availability Overview

A routing configuration we make between two devices with same hardware specs to failover production traffic in the event a device goes down. Two cables used for monitoring are used between such devices to monitor a heartbeat between the configured Master and Slave device. VRRP (protocol 112) traffic is what defines the heartbeat. These are the Keepalives that elects the roles between the cluster devices. If these packets do not see a response from the Slave to the Master, a fault state is triggered. Afterwards, the device will see fit to failover traffic to the Slave device. At that time, the role of the Slave device changes to Master.

VRRP EXPLAINED

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Virtual router Redundancy Protocol is an election protocol that dynamically assigns responsibility for a virtual router to one of the VRRP routers on a LAN. Provides dynamic fail over in the forwarding responsibility should the Master become unavailable. VRRP is a higher availability default path without requiring configuration of dynamic routing or router discovery protocols on every end-host.

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KEEPALIVED EXPLAINED

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Keepalived implements a set of checks to dynamically and adaptively maintain and manage a load balanced server pool according to their health; high-availability is achieved by VRRP protocol. Keepalived implements a set of hooks to the VRRP finite state machine ([1]FSM) providing low-level and high-speed protocol interactions .

There is a keepalived configuration file for both master and slave device. One defines the master and its state as such while the slave is defined as BACKUP state. Also defined is the priority, the virtual interface (2) in which the tests are invoked upon, one test for every virtual interface.

A fault state will be triggered in the event that one of these tests fails. Within the following log can be found the test number that the state is found in. The test number corresponds to the configuration file defining “vrrp_instance” test<#>.

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[1] The FSM is the mechanism used to equate which action or setting implementation is taken for available state, master or backup, able to sense when one state is taken over the other.