.NET Microservices: Architecture for Containerized .NET Applications

Containerization is an approach to software development in which an application or service, its dependencies, and its configuration (abstracted as deployment manifest files) are packaged together as a container image. The containerized application can be tested as a unit and deployed as a container image instance to the host operating system (OS).

Just as shipping containers allow goods to be transported by ship, train, or truck regardless of the cargo inside, software containers act as a standard unit of software deployment that can contain different code and dependencies. Containerizing software this way enables developers and IT professionals to deploy them across environments with little or no modification.

Containers also isolate applications from each other on a shared OS. Containerized applications run on top of a container host that in turn runs on the OS (Linux or Windows). Containers therefore have a significantly smaller footprint than virtual machine (VM) images.

Each container can run a whole web application or a service, as shown in Figure 2-1. In this example, Docker host is a container host, and App1, App2, Svc 1, and Svc 2 are containerized applications or services.

Another benefit of containerization is scalability. You can scale out quickly by creating new containers for short-term tasks. From an application point of view, instantiating an image (creating a container) is similar to instantiating a process like a service or a web app. For reliability, however, when you run multiple instances of the same image across multiple host servers, you typically want each container (image instance) to run in a different host server or VM in different fault domains.

In short, containers offer the benefits of isolation, portability, agility, scalability, and control across the whole application lifecycle workflow. The most important benefit is the environment’s isolation provided between Dev and Ops.

What is Docker?

Docker is an open-source project for automating the deployment of applications as portable, selfsufficient containers that can run on the cloud or on-premises. Docker is also a company that promotes and evolves this technology, working in collaboration with cloud, Linux, and Windows vendors, including Microsoft. Docker containers can run anywhere, on-premises in the customer datacenter, in an external service provider or in the cloud, on Azure. Docker image containers can run natively on Linux and Windows. However, Windows images can run only on Windows hosts and Linux images can run on Linux hosts and Windows hosts (using a Hyper-V Linux VM, so far), where host means a server or a VM.

Developers can use development environments on Windows, Linux, or macOS. On the development computer, the developer runs a Docker host where Docker images are deployed, including the app and its dependencies. Developers who work on Linux or on macOS use a Docker host that is Linux based, and they can create images only for Linux containers. (Developers working on macOS can edit code or run the Docker CLI from macOS, but as of the time of this writing, containers don’t run