Plan a configuration backup, take note on total time required to complete the task, and notify customers about the availability of the services during the execution process. Keep a backup server/service ready in case major outage. Most importantly keep all the stakeholders aware regarding the upgradation process and ensure instant support.

Communicate communicate communicate, and engage your users early and often. The best plan is the one they help test and endorse. Literally everything else is a distant second to having your users vested in the plan, and owning the timing.

Recently we have done a major migration of one of ERP application SAP. We have been planned very detailed way existing system matrix collection and made benchmark with 5 years plan for new system in terms of capacity planning / high availability etc and with sequence of mock migration plan which given lot deep insight and understanding of current system performance / bottleneck / measuring migration strategy and meticulous planning to achieve migration with minimum of business impact. Analysis and record the pre/post system migration using monitor tool and finally getting user feedback and submit the assurance report to management with stability and sustainability of new migrated system

Software upgrade requires a number of planning, validation and testing. While the scale or granularity of the tasks may grow per different projects and platforms, the below steps may always help mitigate the unknown issues: First, analyze and plan the objective to determine what needs to be upgraded and why? Second, get a list of dependencies (other related software, utilties and tools) and all parties, including users being impacted. Next, backup the impacted environment and dependencies as well as all configurations and docs. In additon, test the upgrade in DEV, then in INT, and finally schedule to apply in PROD when all testing pass. Any issue found during DEV or INT should be fixed before scheduling for the final PROD upgrade.