title: ECS not starting tasks even though there is enough capacity
body: <p>I've got a task definition that uses 977MB memory and 1024 CPU, using awsvpc networking:
  <a href="https://i.stack.imgur.com/kjsjR.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/kjsjR.png" alt="Task definition"></a></p>
  
  <p>And I have EC2 instances provided by an Auto Scaling group tied to a Capacity Provider, already running 4 tasks across 4 instances:
  <a href="https://i.stack.imgur.com/ECtpg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ECtpg.png" alt="ECS Instances"></a></p>
  
  <p>But when I launch 2 new tasks on top the 4 that are already running, they get stuck in "PROVISIONING" state. Despite what looks like enough memory and CPU to run the new tasks.</p>
  
  <p>What could be going wrong and where can I look further to debug this?</p>