Advantages of Parallel vs. In-place Upgrade:
1. Low Outage Window - The outage window is very low in Parallel. Since you would already have the new version environment built with migrated configuration from the old version and certificates. You need to switch the traffic from the old to the new environment at the LB or VIP level.
You can add the new version environment to the same LB or VIP pool and remove the old version servers one by one. So, that your client traffic will slowly go to the new version environment.
2. NO Rollback process - If client applications have any issues with the new version environment, the rollback process will be to flip the switch at the Load Balancer to move to the old version environment. You don't need to remove the newer environment or revert to old backups.
3. Easy Troubleshooting - If there are any issues with the newer version environment, we can lose all the corresponding logs and configuration for troubleshooting in case of rollback. Here, the logs and configuration are untouched and can be used for troubleshooting issues.
4. Know issues beforehand - During deployment of a newer environment, it will be easier to catch any issues through smoke or functional tests. No client traffic is needed to validate those.
5. License to set up - Since the newer version environment will be used in the future and with the agreement that the older version environment will be decommissioned eventually. In such cases, we provide Temporary licenses to set up this newer version environment, OR you can use the original license keys provided via email when you purchased them.
NOTE: Copying License keys from one machine to another machine will NOT work.