I would be tempted to skip the Docker part entirely and use raw EC2 instances plus Packer or whatever tool of choice to.deploy the code. You still get autoscal

I would be tempted to skip the Docker part entirely and use raw EC2 instances plus Packer or whatever tool of choice to.deploy the code. You still get autoscaling that way, and additional isolation of processes too. In addition, Amazon handle all the packing of VMs into hosts. With the Docker container route, you're still doing some of that work yourself to minimise waste.