I've noticed that every time you save the configuration via the console a new Task definition gets created. This happens irrespective of whether you are creating/updating a new task and causes the number of active tasks to just grow and grow.

We should perhaps deregister all existing tasks listed under the 'jenkins-slave' family before saving the new set. This way we will only have those tasks that are active in view in the aws console and stop active tasks from just hanging around needlessly.

Note I've submitted a pull request which fixes this issue against the github account.

https://github.com/jenkinsci/amazon-ecs-plugin/pull/27