5/7/2023 0 Comments Cnet dockshelfIf you’ve built a REST API with ASP.NET Core and want to package it into an image, you’ll want to base your image on Microsoft’s ASP.NET Core Runtime image. Usually, images are based on other images, inheriting their layers. Consequently, a layer is a set of file system changes, and an image is a stack of layers that are applied one after the other to produce the final file system state. Each instruction can affect the file system of the image and thus creates a new layer. This file contains instructions on how to create the image. It all begins with a file named Dockerfile. To understand layers, we need to understand how images are created and structured. ![]() Layers is another term we need to define. They also require less disk space because different images can share layers, and containers created from the same image share all layers. They require less CPU and memory, because they don’t run an operating system. This leads us to one advantage of containers over VMs: they require fewer resources. Because of the kernel’s virtualization features, those processes are isolated from each other, but it’s still just a single kernel running them all. The kernel of the host operating system is running the applications that are defined inside the containers. ![]() Thus, we can conclude that all containers must be running on the same kernel. I knew Docker containers were a virtualization, but there’s no virtualized hardware-so what’s being virtualized? Docker virtualizes the operating system’s kernel and the file system. When I started with Docker, this was where I got confused. VMs contain and run their own operating system, including the kernel, while containers don’t. VMs virtualize hardware, like the CPU, memory, or network cards, whereas containers don’t. It can have its own IP address, it isolates its processes from all other containers, and it can contain its changes to the file system.īut that’s where the similarities end. And at first, it does look like a VM since a container is a virtualization concept. Each container would have its own password for the SA user and its own IP address. In a typical software development environment, you could have three SQL Server 2017 containers-one for development, one for staging, and one for production. There’s only one such image, but potentially thousands of containers are created from it. An example of an image is the SQL Server 2017 image from Microsoft. We’ve established that containers are created from images. That short command touched on many aspects we should examine more closely. So, if you get a permission denied error, you probably forgot to use sudo. The commands in the rest of this post will omit the sudofor brevity. When everything is successful, the container prints a short message and then exits.īy default, Docker commands need to be executed as root. It downloads the image hello-world from the Docker registry, creates a container from it, and runs that. To verify that Docker has been installed successfully, execute the Hello World container: sudo docker run hello-world Sudo apt-get install docker-ce docker-ce-cli containerd.io Detailed instructions are available here-here’s the short version: sudo apt-get update ![]() We’re going to set up Docker on a Ubuntu machine. Just like a class definition in the OOP world, an image defines the structure, which the container then parametrizes.īefore we continue this deep dive into the theory of what Docker is, let’s first set it up and do some hands-on experiments. You can think of images as class definitions and containers as class instances. An image bundles all relevant executables, libraries, and configuration files of the application.Ī container is a specific instance of such an image. The heart of Docker is that you can package applications in so-called images, giving the applications a well-defined environment to run in. So, what is Docker? According to Wikipedia, “Docker is a set of coupled software-as-a-service and platform-as-a-service products that use operating-system-level virtualization to develop and deliver software in packages called containers.” Let’s pull that apart and understand what it really means. NET developer, at some point in your career, you’ll most likely come across Docker for. Whether you’re a junior developer just starting out or a seasoned. Docker: it’s one of those technologies that seems to be everywhere.
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