Is it possible to have exactly one task running in AWS ECS at all time? I don't want to have Blue/Green kind of deployment.
My Requirement:
Min/Desired/Max task = 1;
When I redeploy ECS service, then it should first stop old task and then spin new task. Currently it does opposite.
Any reference would be helpful.
Yes it is possible.
You can create an ECS Service with Number of Tasks as 1 that will set the desired count to 1.
Since you want only 1 task and that should stop and then a new one should come, you can modify the Deployment Configuration with below values:
Minimum Healthy Percent - 0
Maximum Percent - 100
With Desired Count as 1, Minimum Healthy Percent as 0 and Maximum Percent as 100, ECS Service will kill the already running task and then create a new task.
Note: Service will de down during this time.
To explain the behavior you noticed, The default values are
Minimum Healthy Percent - 100
Maximum Percent - 200
and with Desired Count as 1, in this case ECS Service will maintain one running task at all times since Minimum Healthy Percent is 100 i.e. 100% of 1 is 1. However, Maximum Percent as 200 allows ECS Service to create another task as 200% of 1 is 2. So a new task is started first and once this task is stable the old task is stopped.