We're working on importing our old cloudformation stacks (and soon migrating away from them). This cloudformation stack had failed an update earlier due to a bad config, and is currently in UPDATE_ROLLBACK_COMPLETE state. We're getting this opaque error on

pulumi up

aws:cloudformation:Stack (ec2Stack):
      error: 1 error occurred:
      	* updating urn:pulumi:env::project::aws:cloudformation/stack:Stack::ec2Stack: 1 error occurred:
      	* error waiting for CloudFormation Stack update: failed to update CloudFormation stack (UPDATE_ROLLBACK_COMPLETE): []

Any ideas?

This is sort of a lack of compatibility between the two products. You'll have to get the cfn stack into a state where it can be updated to move forward

Gotcha -- thanks!