What is the difference between Azure Container Service and Web App for Containers?
They both seem to offer a fully managed platform on which we can deploy containers. I feel that Web App for Containers must be offering something more, but I don't see it. I've read the Azure Container Service FAQ and the Web App for Containers intro page, but the difference is not obvious to me.
Web App for Containers lets you run your custom Docker container which hosts your Web Application. By default the Web App Service with Linux OS provides built-in Docker images like PHP 7.0 and Node.js 4.5. But by following the instructions from this webpage you can also host your custom docker images which allows you to define your own SW-Stack. The limitation is that you can only deploy one docker image to an App Service. You can scale the App Service to use multiple instances, but each instance will have the same docker image deployed. So this allows you to use Docker as a Service, but isn't intended for deploying Microservices.
Container Services (ACS), Kubernetes Service (AKS) and Service Fabric allow you to deploy and manage multiple (different) Docker containers which might also need to communicate with each other. Let's say you implement a shopping website and want to build your web application based on a Microservices architecture. You end up having one Service (= container) which is used for registration & login of users and another Service which is used for the visitors' shopping carts and purchasing items. Additionally you have many further small services for all the other needed tasks. Because the purchasing service is used more frequently than the sign-up/sign-in service, you will need, for example, 6 instances of the sign-up/sign-in service and 12 instances of the cart service. Basically, ACS, AKS and Service Fabric let you deploy and manage all those different Microservices.
If you want to know the difference between ACS/AKS and Service Fabric you might want to have a look here.