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Docker is a platform for packaging, deploying, and running applications. Docker applications run in containers that can be used on any system: a developer’s laptop, systems on premises, or in the cloud.is a technology that’s been around for a long time, but it’s seen new life with. It packages applications as images that contain everything needed to run them: code, runtime environment, libraries, and configuration. Images run in containers, which are discrete processes that take up only as many resources as any other executable.It’s important to note that Docker containers don’t run in their own virtual machines, but share a Linux kernel.
The first solution we tried for mitigating this security risk was docker-squash, an open source tool that combines Docker layers by deleting files only used in intermediate build steps. Once part of our workflow, docker-squash removed secrets, but doubled image build time.
Compared to virtual machines, containers use less memory and less CPU.However, a Linux runtime is required for Docker. Implementations on non-Linux platforms such as macOS and Windows 10 use a single Linux virtual machine. The containers share this system.has enjoyed widespread adoption because of its. Consistent test environment for development and QA. Cross-platform packages called images. Isolation and encapsulation of application dependencies.
Ability to scale efficiently, easily, and in real time. Enhances efficiency via easy reuse of images.We’ll look at these basic concepts as we install the Docker tools, and create images and containers. Get Started with DockerWe’ll start by installing the Docker desktop tools found Download the correct installer for your operating system and run the installation. Running a containerOnce we install the tools, we can run a Docker image:docker run hello-world does exactly what it sounds like. It runs an image named 'hello-world.' Docker looks for this image on our local system.
When it can’t find the image, Docker downloads it from for us.Hello-world displays a message telling us everything’s working. Then it spells out the process for us before recommending some additional steps. Under the coversLet’s take a look at a few more Docker commands that tell us more about the environment.docker ps -a lists the containers on our system:From this, we can see that the hello-world container is still in memory. The status column tells us that it’s exited. The names column has a name, kindbose, that Docker assigned to the container for us. We’ll cover container names below.Let’s run this image again with docker run hello-world. The output is almost the sameexcept this time we don’t see information about downloading the image.
It was already available on our system.But what does docker ps -a show us now?We see two stopped instances of hello-world, with two different names. Docker created an additional container. It didn’t reuse the first. When we told Docker to run an image named hello-world, it did exactly that; it ran a new instance of the image. If we want to reuse a container, we refer to it by name.
Reuse a containerLet’s try starting one of the stopped containers:This time, we used docker start –attach instead of docker run. We use the start command, and rather than naming the image, we specify the name of a container that’s already loaded. The –attach tells Docker to connect to the container output so we can see the results.We stop containers with docker stop and remove them with docker rm. We’ll take a look at that below when we work with applications designed to keep running in the background.If we check docker ps again, we still see two containers.Let’s run a container that doesn’t exit immediately.
Hello-world’s instructions gave us an interesting example:With a single Docker command, docker run -it ubuntu bash, we downloaded an Ubuntu Linux image and started a login shell as root inside it. The -it flags allow us to interact with the shell.When we open another window and list containers, we see a different picture:The Ubuntu container’s status is Up. Let’s see what’s going on inside:docker top looks inside the container and shows us the running processes. The Ubuntu container is running a single process—the root shell.Let’s look at one last Docker command before we create a container of our own:Docker image ls produces a listing of images on our system. We see Ubuntu and the single hello-world image since we only needed that single image to run two containers. Share system resources with a containerSo far, we’ve run a couple of self-contained images.
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What happens when we want to share local resources from our host system with a container? Docker has the ability to share both the file system and the networking stack with containers.Let’s create a web server that serves a web page from the local filesystem. We’ll use a public Nginx image.First, we need an HTML file to display when we connect to the web server. Start in an empty directory that we’ll call my-nginx and create a single subdirectory named html. Inside html, create index.html.