Customer is currently running ISE 2.1, fully-distributed, and needs to upgrade to 2.2 in order to gain Hyper-V support due to the server team changing hypervisor strategy. Customer wants to control the upgrade process, site by site, as opposed to letting the GUI-based "wizard" roll out the upgrade across the deployment.
I understand the upgrade sequence to be:
1. Secondary Admin Node
2. Primary Monitoring Node
3. Policy Service Nodes
4. Secondary Monitoring Node
5. Primary Admin Node
1. Is the CLI the best method to achieve the fine-grained control the customer is looking for?
2. If it is, and let's say steps 1 and 2 (above) are completed successfully, how long can the customer take to complete the rest of the nodes?
2a. For example, can they upgrade the PSN's at the first site one weekend, then wait to perform the upgrade of the next site's PSN's the following weekend, etc., until finally upgrading the Primary Admin Node a month or so after the start of the overall upgrade process?
2b. If so, what risks or caveats are there to running in this split-version capacity for multiple weeks?