Instance Scheduler starting all instances belonging to a schedule irrespective of maintenance window

[hammadraza66]

Describe the bug

When multiple maintenance windows configured in an account and are scheduled to be executed at different times - instance scheduler starts all the instances belonging to all the maintenance windows at the same time, irrespective of maintenance window time.

To Reproduce

• Created separated maintenance windows to be executed at different times.
• Different instances were targeted for different maintenance windows.
• All of the instances including ones belonging to maintenance window and ones not belonging to maintenance window are tagged with same schedule name as configured in DDB table.
• Updated the applied schedule in instance scheduler DDB config table by adding use_maintenance_window: True(Boolean) and ssm_maintenance_window(StringSet) name_of_maintenance_window1 as field 0 and name_of_maintenance_window2 as field 1.

Expected behavior

Instance Scheduler should start the instances ONLY belonging to a specific maintenance window at given time BUT not all the instances belonging to all the maintenance windows.

Please complete the following information about the solution:

• Version: [3.0.11]
• Region: [af-south-1]
• Was the solution modified from the version published on this repository? No

[shujacks]

Thanks for reaching out, we will look into this and respond shortly.

[hammadraza66]

Hi, any update on this please?

[CrypticCabub]

Apologies for the delay, I have been OOO for the last week for personal reasons.

This currently is the designed behavior of the solution in regards to maintenance window integration. Instance Scheduler does not attempt to reverse-engineer which maintenance windows are attached to which instances to determine if the window should be applied. The intended mental model is that the SSM maintenance window is being attached to the schedule and thus should apply to all EC2 instances that are subject to that schedule regardless of if the window has any other attachment method to the instance.

[hammadraza66]

This behaviour seems not the true SSM Maintenance window integration causing a lot of confusion and should be clearly documented. ssm_maintenance_window type as StringSet and allowing multiple fields as maintenance window name each, gives the idea that instance scheduler would respect the each maintenance window added to a single schedule.

Suggestions/Documentation Update Request for existing behavior

• Either change the type to String and customer should be clearly advised to provide only one single maintenance window per schedule.
• Or remove the ssm_maintenance_window altogether and only keep use_maintenance_window. If set to True, IS would just start all the instances as per ANY configured MW in the account - exactly like it is doing today.

Feature Request

• When multiple MWs provided in a schedule, Instance Scheduler should only start the instances belonging to a specific maintenance window as per MWs time - rather than starting all the instances belonging to different MWs at the same time.