The minimum healthy instance type:
HOST_COUNT: The minimum number of healthy instance as an absolute value.
FLEET_PERCENT: The minimum number of healthy instance as a percentage of the total number of instance in the deployment. In an example of nine instance, if a HOST_COUNT of six is specified, deploy to up to three instances at a time. The deployment will be successful if six or more instances are deployed to successfully; otherwise, the deployment fails. If a FLEET_PERCENT of 40 is specified, deploy to up to five instance at a time. The deployment will be successful if four or more instance are deployed to successfully; otherwise, the deployment fails.
In a call to the get deployment configuration operation, CodeDeployDefault.OneAtATime will return a minimum healthy instance type of MOST_CONCURRENCY and a value of 1. This means a deployment to only one instance at a time. (You cannot set the type to MOST_CONCURRENCY, only to HOST_COUNT or FLEET_PERCENT.) In addition, with CodeDeployDefault.OneAtATime, AWS CodeDeploy will try to ensure that all instances but one are kept in a healthy state during the deployment. Although this allows one instance at a time to be taken offline for a new deployment, it also means that if the deployment to the last instance fails, the overall deployment still succeeds.