Docker is an open-source virtualization technology known a containerization platform for software containers. These containers provide a means of enclosing an application, including its own filesystem, into a single, replicable package.
Initiated in 2013 by Solomon Hykes, the Docker platform was built specifically for Linux operating system and has since achieved widespread popularity among developers and cloud service providers for its ability to simplify and automate the creation and deployment of containers.
Because container technology allows developers to package an application, along with all of its dependencies, into a standardized unit, containers are quickly becoming a preferred approach to virtualization. Automation through Docker has been critical to that success.
What Is a Docker Container?
Containers are not a new technology. Like virtual machines (VM), they are a form of virtualization that has been around for years. However, where they stand apart from a VM is in the size of their footprint.
While a VM creates a whole virtual operating system, a container brings along only the files that are required to run an app and that aren’t already running on the host computer. They can run lean by sharing the kernel of the system they run on, and where they can, they even share dependencies between apps. Ultimately, that means smoother performance, smaller application size, and faster deployment.
Docker Container FAQ
What if your Docker container refused to connect? There are a number of reasons why your Docker container may refuse to connect. For example, you may need to publish the exposed ports using the following option: -p (lower case) or --publish= that will tell Docker to use ports you manually set and map them to the exposed container's ports. This is important because you already know which ports are mapped rather than inspecting which ones and making adjustments. Another common issue is if you're running proxy redirects on nginx and they are not on the same network. In this scenario, you may need to create your own network and add both containers to it using Docker run commands.
What does it mean if the Docker name is already in use by the container? This is a common problem encountered by new Docker users. It means you may have started a container in the past using the same parameters. You can either delete the first container or choose a new name for the container.
What does it mean if I get an error for unable to load the service index for source? This is a problem that Docker users encounter when there are multiple network adaptors present for the host and the priority of the adaptor is misconfigured. You can run a command to display the network adaptors and troubleshoot, and in some instances check to see you have the most up-to-date SDK installed.
What Is Docker Engine?
The Docker container is the component that delivers efficiencies, and Docker Engine is what makes it all possible. In short, a Docker container is run from an image file — essentially a file that’s created to run a particular application on a particular operating system. Docker Engine uses that image file to build a container and run it.
The lightweight Docker Engine, and the easy automation it provides, is the real innovation that has made Docker a successful tool. Its ability to automate deployment of containers has brought the technology to prominence. It offers the benefit of greater scalability in virtualized environments, and it allows for faster builds and testing by development teams.
What is Docker Compose?
Docker compose is a tool used to define and run multi-container applications with Docker. You can quickly use a single command to create or start all services from your configuration using Docker compose and a YAML file.
Examples of common Docker compose queries include:
- Docker compose logs
- Docker compose logs follow tail
- Docker compose memory limit
- Docker compose network name
- Docker compose tags
Docker Config File Location
The default Docker config file location is: %programdata%\docker\config\daemon. json.
How Does Docker Contribute to a DevOps Environment?
DevOps teams gain a number of advantages by using Docker. With instant OS resource startup and enhanced reliability, the platform is well-suited to the quick iterations of agile development teams. Development environments are consistent across the whole team, using the same binaries and language runtime.
Because containerized applications are consistent across systems in their resource use and environment, DevOps engineers can be confident an app will work in production the same as it does on their own machine. Docker containers also help to solve compiling issues and simplify the use of multiple language versions in the development process.
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