Container Service produces and manages Elastic Compute Service (ECS) instances by means of your authorization. Your containers can only run on the ECS instances that you own.
If the cluster is of the classic network, the access between clusters of different users is isolated by security groups.
If the network type of the cluster is Virtual Private Cloud (VPC), the access between clusters of different users is isolated by VPC.
You can customize the security groups or VPC access permissions of the clusters that you own.