• The first 5 hosts that join the VMware HA cluster are automatically selected as “primary nodes
• All the others are automatically selected as “secondary nodes”
• When you do a reconfigure for HA the primary nodes and secondary nodes are selected again, this is random

What’s up with these primaries and secondaries?

• Primary nodes hold cluster settings and all node states which are synced between primaries
• Secondary nodes send their state info(resource occupation) to the primary nodes
• Nodes send heartbeats to each other, primary nodes send heartbeats to primary nodes only and secondary also only to primary. And they do this every second. (Which is a changeable value: das.failuredetectioninterval)

So what if a primary node fails, will a secondary be promoted?

• No, there will only be a new primary appointed when the failed one is removed from the cluster. A secondary will be promoted to primary at random.

But what if all my primary nodes fail?

• This is an unaddressed issue, that’s the reason why you can only account for 4 host failures within a cluster! There needs to be at least one primary!

So when does the gateway come in play?

• Actually the gateway, which is the default “isolation address”, will only be used when an isolation has occurred. So when the AAM client thinks it’s isolated it will check the isolation addresses.

From — Yellow Brick — a very lovely VMWare oriented site.