When your organization is upgraded, Secure Agent groups A and B are upgraded simultaneously. Within each Secure Agent group, Process Server is upgraded sequentially. Therefore, while Process Server is being upgraded on agents A1 and B1, it remains up and running on agents A2 and B2. When the upgrade finishes on agents A1 and B1, Process Server is upgraded on agents A2 and B2.
Data Integration Server and Mass Ingestion do not support rolling upgrades. In groups A and B, Data Integration Server is upgraded on each agent simultaneously. In group B, Mass Ingestion is upgraded on agents B1 and B2 simultaneously.