VM1 runs a 24/7 line-of-business app and you plan these changes: change size from D4s v3 to D8s v3; add a 500-GB managed disk; install the Puppet Agent extension; enable Desired State Configuration. Which of these changes will cause VM1 to experience downtime?

Changing a VM's size, especially to a different series or one with more vCPUs/memory, typically requires a deallocation and reallocation of the VM. This process involves a restart, leading to downtime. Adding a managed disk is an online operation and does not cause downtime. Installing the Puppet Agent extension is also an online operation performed by the Azure VM Agent, which doesn't interrupt the VM's running state. Enabling Desired State Configuration (DSC) applies configurations to the VM's operating system without requiring a restart.