System upgrade under high availability constraints

摘要

An embedded step is executed to upgrade multiple layers of a system. The embedded step includes multiple nested steps, and each nested step includes a sequence of actions for upgrading one of the layers. A finite state machine defines the state transitions for each nested step. During the execution of the nested steps, an outer step of the nested steps is transitioned from an executing state into a waiting state after the outer step completes a tear-down. During the transitioning of the outer step, the outer step sends a trigger to an inner step of the nested steps to cause the inner step to transition into the executing state. When the inner step is completed, the outer step is transitioned out of the waiting state to execute a build-up phase. Execution of the embedded step is completed when an outermost step of the nested steps is completed.