If you need to fail and scale independently.
-you can use small EC2 instances behind an application load balancer and within autoscaling groups with host based routing for request routing.
- converting a stand-alone api to a container is not rocket science and nor should it require any code rewrite.
- if you need to run scheduled Docker containers that can also be done with ECS or if it is simple enough lambda.
- the first thing you should worry about is not “containerization”. Its getting product market fit.
As far as needing containerization for orchestration, you don’t need that either. You mentioned Nomad. Nomad can orchestrate anything - containers, executables, etc.
Not to mention a combination of Consul/Nomad is dead simple. Not saying I would recommend it. In most cases (I’ve used it before), but only because the community and ecosystem is smaller. But if you’re a startup, you should probably be using AWS or Azure anyway so you don’t have to worry about the infrastructure.