您可以编写一个Shell脚本并将其附加到启动ECS任务的docker容器中，以定期清理旧容器。下面是一个示例脚本：

#!/bin/bash

# Keep the last 5 containers running
NUM_CONTAINERS=5

# Get all running containers that are not the current one
containers=($(docker ps -q --no-trunc --filter "status=running" --filter "name!=`hostname`"))

# Sort the list of containers by creation date, oldest first
container_list=$(for container in ${containers[@]}; do
    echo $container:$(docker inspect --format='{{.Created}}' $container)
done | sort --key 2)

# Delete older containers if there are more than NUM_CONTAINERS
if [[ ${#containers[@]} -gt $NUM_CONTAINERS ]]; then
    for ((i=0; i<${#containers[@]}-$NUM_CONTAINERS; i++)); do
        container_to_delete=$(echo "${container_list}" | head -n 1 | cut -f1 -d':')
        docker stop $container_to_delete
        docker rm $container_to_delete
        container_list=$(echo "${container_list}" | tail -n +2)
    done
fi

将此脚本保存为cleanup_containers.sh并将其添加到您的Docker镜像中，以便它在每次启动容器时运行：

FROM amazonlinux:latest

COPY cleanup_containers.sh /usr/local/bin/
RUN chmod +x /usr/local/bin/cleanup_containers.sh

ENTRYPOINT ["/usr/local/bin/cleanup_containers.sh"]

请注意，这只会删除旧容器，而不会删除旧图像或其他数据。如果容器占用大量磁盘空间，则可能需要手动清理它们。

最后，在您的ECS任务定义文件中添加"memory": 64以限制每个容器可用的内存量。这将确保一个容器不会消