title: What is the minimum healthy percent and maximum percent in Amazon ECS
body: <p>I already have the experience in Docker and EC2. But I'm new to ECS. Can someone help me to understand what these two parameters actually does, their difference and usage.</p>
  <p><a href="http://docs.aws.amazon.com/AmazonECS/latest/developerguide/update-service.html" rel="noreferrer">Official Docs</a> says:</p>
  <blockquote>
  <p>The <strong>minimum healthy percent</strong> represents a lower limit on the number of your service's tasks that must remain in the RUNNING state during a deployment, as a percentage of the desired number of tasks (rounded up to the nearest integer). This parameter enables you to deploy without using additional cluster capacity. For example, if your service has a desired number of four tasks and a minimum healthy percent of 50%, the scheduler may stop two existing tasks to free up cluster capacity before starting two new tasks. Tasks for services that do not use a load balancer are considered healthy if they are in the RUNNING state; tasks for services that do use a load balancer are considered healthy if they are in the RUNNING state and the container instance it is hosted on is reported as healthy by the load balancer. The default value for minimum healthy percent is 50% in the console and 100% for the AWS CLI, the AWS SDKs, and the APIs.</p>
  <p>The <strong>maximum percent</strong> parameter represents an upper limit on the number of your service's tasks that are allowed in the RUNNING or PENDING state during a deployment, as a percentage of the desired number of tasks (rounded down to the nearest integer). This parameter enables you to define the deployment batch size. For example, if your service has a desired number of four tasks and a maximum percent value of 200%, the scheduler may start four new tasks before stopping the four older tasks (provided that the cluster resources required to do this are available). The default value for maximum percent is 200%.</p>
  </blockquote>
  <p>I still didn't get a clear idea about these two parameters.</p>
  <ol>
  <li>With minimum healthy percent, if my service has a desired number of 4 tasks and a minimum healthy percent of 25%, how many existing/new tasks will the scheduler start/stop?</li>
  <li>With maximum percent, if my service has a desired number of 4 tasks and a maximum percent value of 50%, how many existing/new tasks will the scheduler start/stop?</li>
  <li>If my service has only one task running, how to set these parameters to get existing task stopped and new task running.</li>
  </ol>