Single host in the cluster on a differing IP range, is this supported or best practice? Will it cause any issues with host isolation response etc?

[lukeglazebrook]

Just started working at a new company, part of the infrastructure is semi hosted by a third party who I have not been impressed with so far (only 4 host and managed with their own VC).  Three of the host all have their management on the same range i.e..

Cluster A

Host 1 176.74.183.1

Host 2 176.74.183.2

Host 3 176.74.183.3

The fourth however is ...

Host 4 83.137.132.221

Is this a supported configuration with a load of hosts in the same cluster?  Feels a tad wrong to me, any opinions ?  

[rcporto]

The fourth host has access to the same datastores and networks of the other three hosts ?? If not, I can't see a reason why maintain that host inside the cluster since you will not be able to use cluster features like HA and DRS.

[shivendraj]

Management IP should not be any issue in your case. But if you need the features to be enabled in the cluster then there might be an issue like connecting for the default gateway for HA or for enabling vMOtion in the cluster to support HA.

[lukeglazebrook]

Hmm,

The company also only has a single datastore configured for heartbeat, I'm wondering if this further increases the chances of HA not working? 

[vHaridas]

HA will work with single Datastore also.

Just make sure you use same IP subnet for management network to avoid issues.

[lukeglazebrook]

Currently its different, i.e the single host is using a completely different gateway.  I'm trying to figure out what would be a worse case scenario under these conditions

[vHaridas]

if Hosts are in different Network then Chances of Host isolation and Network partition would be high. HA may work fine as long as you don't have any network disturbance and hosts continue to communicate on management network 

Network Partition - VMware vSphere 5.1

When a management network failure occurs for a vSphere HA cluster, a subset of the cluster's hosts might be unable to communicate over the management network with the other hosts. Multiple partitions can occur in a cluster.

A partitioned cluster leads to degraded virtual machine protection and cluster management functionality. Correct the partitioned cluster as soon as possible.

Virtual machine protection. vCenter Server allows a virtual machine to be powered on, but it is protected only if it is running in the same partition as the master host that is responsible for it. The master host must be communicating with vCenter Server. A master host is responsible for a virtual machine if it has exclusively locked a system-defined file on the datastore that contains the virtual machine's configuration file.

Cluster management. vCenter Server can communicate with only some of the hosts in the cluster, and it can connect to only one master host. As a result, changes in configuration that affect vSphere HA might not take effect until after the partition is resolved. This failure could result in one of the partitions operating under the old configuration, while another uses the new settings.

If a vSphere HA cluster contains pre-ESXi 5.0 hosts and a partition occurs, vSphere HA might incorrectly power on a virtual machine that was powered off by the user or it might fail to restart a virtual machine that failed.

vSphere HA Agent is in the Network Isolated State vSphere Documentation Center

The vSphere HA agent on a host is in the Network Isolated state. User intervention is required to resolve this situation.

Problem

When a host is in the Network Isolated state, vSphere HA applies the power-off or shutdown host isolation response to virtual machines running on the host. vSphere HA continues to monitor the virtual machines that are left powered on. While a host is in this state, vSphere HA's ability to restart virtual machines after a failure is affected. vSphere HA only powers off or shuts down a virtual machine if the agent on the host determines that a master host is responsible for the virtual machine.

Cause

A host is network isolated if both of the following conditions are met:
Isolation addresses have been configured and the host is unable to ping them.
The vSphere HA agent on the host is unable to access any of the agents running on the other cluster hosts.

To avoid such issues, its recommended to keep management network in same subnet.