VPNGatewayRoutePropagation dependency while creating TransitGatewayAttachment

[manuelnucci]

I have a CloudFormation stack that needs to be updated. Particularly, we're migrating from VPNGateway to a TransitGateway and we face a particular challenge. In the Change Set to generate we have removed the references to the VPN Gateway and its related resources. This will tell CF that all the resources should be planned to be deleted. So far no problem with that.

Now we want to add the TransitGatewayAttachment as a new resource in the same stack. The problem is that some routes cannot be added until the auto-propagation of the old resource (VPNGatewayRoutePropagation) has been completely removed. For that effect, we would need that the TransitGatewayAttachment waits for the VPNGatewayRoutePropagationto be removed, but we no longer have its reference in the code.

Ideally this should be a one-step operation because we want to minimize downtime as much as we can. I've already thought about a workflow like the following, but that would be a plan B for the moment:

1. Deploying CF with VPN Gateway missing (deleting the resource).
2. Manually confirming the deletion.
3. Deploying new CF with TransitGatewayAttachment.

The problem here is that the two-step operation will generate a higher downtime.

Is there any way to define that dependency using DependsOn, WaitCondition, etc.?