Nimbostratus
Altostratus
Global Traffic Manager will definately help you to provide high availability between your datacenters. Most of your points are correct, but here are some corrections:
- Yes, you need at least one GTM per site. They will run as standalone devices, but will be configured in a sync group that will enable them to work together for resolution.
- iQuery is an F5 Networks, UDP-based protocol that collects configuration and metric information and exchanges that information between 3-DNS Controllers and other F5 Networks products running the big3d agent.
- iQuery replicates any configuration changes between the GTMs. But, each device keeps its own copy of the configuration. GTM only does DNS resolution, although in a much more intelligent way than standard BIND does. If a failover happens, new DNS queries will be resolved to alternate addresses.
- if the internal heart beat is lost, the boxes will assume the other site is down, and not give out address resolutions for that site. Could be an issue if you run an active/ cold standby datacenter scenario. Not so much an issue, if it is a hot standby site.