New ecs deploys without downtime

Question

I have an ECS - EC2 configuration with a single task.

How can I launch a new version of the task so that there is no downtime, i.e. this version of the task is only replaced when the new version is 100% active? This way, I avoid as little downtime as possible.

This would solve two problems.

1. No downtime when uploading new versions of tasks.
2. I'm using SPOT and this would avoid changing instances before the service/task is available.