Although I would agree that services such as EC2 are not cost effectively for 1:1, this argument is somewhat invalidated when you consider $5 instances from Doc

Although I would agree that services such as EC2 are not cost effectively for 1:1, this argument is somewhat invalidated when you consider $5 instances from DockerOcean. $100/month for 20 concurrent VMs is enough to replicate even the most complex of deployments. But if you're running on a shoestring, in which case it's probably not production critical, then sure containerisation might be useful too. Also remember that Docker is not a container deployment system, and afaik, they don't advertise themselves as such (though they also don't make much effort to explain this explicitly either)