Change sets let you preview how proposed changes affect a stack before ROS applies them. You can create multiple change sets for a stack in Resource Orchestration Service (ROS) to meet your business requirements.
What is a change set
A change set captures the proposed changes to a stack template and shows you how those changes will affect stack resources. Before ROS applies any changes, you can review exactly what will be added, modified, or deleted. ROS makes the changes to your stack only after you execute the change set. For more information, see Data structures.
Scenarios
Use a change set to create a stack
When you need to manage a large number of cloud resources and want to verify the expected state before a stack goes live, use a change set together with the resource import feature. Import your existing cloud resources into a stack using resource import, then create a change set to preview how the stack will manage those resources. The stack begins managing resources only after you execute the change set. Before executing, you can review and adjust the stack template as needed.
For more information, see Create a stack from existing resources.
For more information, see Create a stack using a change set.
Use a change set to update a stack
When you want to verify the impact of a stack update before it takes effect — for example, to check whether key resources will be deleted or replaced — create a change set instead of updating the stack directly. The change set shows you what will change. The update takes effect only after you execute the change set. Before executing, you can review and modify the stack template to confirm it meets your requirements.
For more information, see Update a stack by using a change set.
Limits
Change sets can only update stacks that are in specific states. For more information, see Update a stack by using a change set.
Each stack can have up to 20 change sets.
Change sets show what changes will be made to a stack, but do not indicate whether those changes will succeed.
A change set does not check for account limit violations, updates to non-updatable resources, or insufficient permissions — any of which can cause a stack update to fail. If a stack update fails, ROS attempts to roll back your resources to their original state.
Change set vs. direct update
Compared with updating a stack directly, updating via a change set provides additional control. For more information, see Update a stack by using a change set, and Update a stack.
Changes take effect only after you explicitly execute the change set — ROS does not apply them automatically.
You can preview the exact impact of proposed changes before anything is modified.
You can review and edit the stack template before committing to the update.
Related topics
View the impacts of a change set and inspect the stack template. For more information, see View a change set, and Data structures.
After you execute a change set, ROS automatically deletes the other change sets associated with that stack. For more information, see Execute a change set.
If a change set no longer meets your requirements, delete it before it is executed. For more information, see Delete a change set.