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Network Design for N+1 Failover

The design of the host network is critical to a successful failover configuration.

The essential concept of active-active failover is that resources that are required for a cluster to serve client

requests are organized into "failover groups". For any cluster, the required resources include:

l the cluster object and all objects to which it points including server pools, server instances, servers,

responders, certificates, etc.

l the subnet on which the cluster IP address resides

l the subnet (or subnets) on which all server IP addresses in the server pool reside

If you instead locate a cluster IP address on one subnet and the servers in the cluster’s server pool all reside on

another subnet, then both those subnets would be considered part of the cluster’s failover group.

So, in order to allow each cluster to fail over separately to another Equalizer, the cluster IP address and all server

IP addresses need to be located on Equalizer subnets that are distinct from the subnets on which other cluster and

server IP addresses reside.

Once you configure cluster and server IPs and enable active-active failover, the clusters, servers, subnets, etc.,

are organized into "failover groups" that can be passed between all the peers at network connectivity issues occur.

How a Peer is Chosen for Failover in N+1

Configuration

A failover occurs when Equalizer detects that there is an issue with one of the subnets on which a cluster’s IP

address or one of its server IP addresses resides. This typically means that Equalizer has lost connectivity on a

subnet, and can happen for any number of reasons; for example, the failure of a downstream hub, router, or other

networking device.

A failover event can be simulated by either removing a cable from Equalizer’s front panel or rebooting a peer.

In our example configuration, each VLAN subnet is connected to Equalizer through a separate port. When you

remove a cable from Equalizer, it recognizes that it has lost connectivity on that subnet and attempts to fail over all

the resources on that subnet (the "failover group") to another peer.

When Equalizer detects a network connectivity failure, it does the following:

1. It determines which failover groups are affected by the failure.

2. It examines the heartbeat information it has received from the other peers in the failover set, and determines

which other peers can provide connectivity on the subnets that have failed.

3. If there is only one peer that can provide the required connectivity, the failover group is moved to that peer.

4. If there is more than one peer that can provide the required connectivity, Equalizer checks the ‘preferred

peer’ setting on the cluster (or clusters) in the failover group (or groups), and if the preferred peer can provide

connectivity, the failover groups are moved to that peer.

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Coyote Point Systems Equalizer Especificaciones Pagina 461