I wonder if there is a race condition between creating an aws.ecs.Service and creating a targetGroup/loadBalancer pair? I'm getting

aws:ecs:Service (ashewor-dashboard-server):
    error: Plan apply failed: InvalidParameterException: The target group with targetGroupArn arn:aws:elasticloadbalancing:us-west-2:948428744612:targetgroup/d5edc351-9ae5dfc/e8cbb3f112d1b253 does not have an associated load balancer.

(and when I run again it works).

I had this problem this week. Had to add this option

dependsOn: [loadBalancer] }

You added that to

ecs.Service

?