AWS VPC main table is for non explicitly associated subnets, you can have 200 route tables with 50 routes each.

When you create a VPC, it automatically has a main route table. 
The main route table controls the routing for all subnets that are not explicitly associated with any other route table. 
On the Route Tables page in the Amazon VPC console, you can view the main route table for a VPC by looking for Yes in the Main column.

I assume you are talking about scenario #2 in this doc https://aws.amazon.com/blogs/containers/optimize-ip-addresses-usage-by-pods-in-your-amazon-eks-cluster/

In that case you do not need a route per node, but a route per private subnet where your nodes secondary ENI's will be on.

Hello,

Fargate is available for for ECS and EKS, it's basically running your container on servers from AWS that you don't have to manage.

I don't know your exact details but the trade off is this (according to my knowledge):

If your usage of a server instance for your container is less than 70% for the whole period it's cheaper to use fargate.

If you factor the time spend on managing servers or the scaling then probably it's even lower.

You can start tasks in ecs/eks fargate and then have the task shut down and deprovision.

What you would do (for ecs) is setup a task definition and then call the api to start a task (one or more containers) with a specific command ( process.sh arg ), after it is done it will shutdown.

Services on the other hand will run all the time.

You cannot use this strategy to run a web app with containers, you can with serverless.

Hope it helps, let me know if you have any other questions