Is docker a container?

Docker is not a container; a container is a standard unit for packaging code and all dependent software for development, delivery, and deployment, so that applications can run quickly and reliably from one environment to another, while docker It is an implementation of container technology and an open source application container engine used to manage containers.

The operating environment of this tutorial: linux7.3 system, docker version 19.03, Dell G3 computer.

Docker is not a container

The relationship between Docker and containers

Now when it comes to containers, The first thing that comes to mind is Docker, but containers are not the same as Docker. Docker is just an implementation of container technology, used to manage containers, just like VMware is an implementation of virtual machines. In addition to Docker, there are also LXC/LXD , rkt and other container technology implementations, but Docker is the most famous.

What is a container

Docker’s official explanation of containers, in one sentence, a container (Container) is to package software into standardized units. for development, delivery and deployment. Containers are standard units for packaging code and all of its dependent software, allowing applications to run quickly and reliably from one environment to another. A container image is a lightweight, executable, independent software package that contains everything needed to run the software: code, runtime environment, system tools, system libraries, and settings. Containerized software is available for Linux and Windows-based applications and runs consistently in any environment. Containers give software independence, isolating it from its environment and ensuring that it runs uniformly across disparate environments such as development and staging environments.

Containers are also a technology used to package application (compiled) code and dependencies required for runtime. Each container run can be repeated, and standardization through the inclusion of dependencies means that you will get the same behavior in any environment you run the container. Containers separate applications from host infrastructure, making them easier to deploy across different cloud and operating system environments. Containers are immutable and the code of a running container cannot be changed. If a containerized application needs to change, a new container needs to be built containing the changes, and the container needs to be re-created from the updated image.

Container technology essentially isolates and controls system resources, allowing the container process to run in its own independent namespace. Containers can have their own file system, network configuration, process space, etc. The process in the container runs in an isolated environment. It is like operating in a system independent of the host, which also makes the container very convenient. of runs anywhere.

Advantages of containers

The main advantages of containers are summarized as follows:

• Easy and efficient to use: Compared with virtual machine images , container images are easier to use and more efficient. Containers are small in size and fast to start, and do not need to be bound to external infrastructure environments, perfectly solving the consistency problem from development to production environments.

• Monitoring and management: Containers are more transparent than virtual machines and facilitate monitoring and management. In particular, the life cycle of the container process is managed by the infrastructure rather than hidden inside the container by the process manager. Finally, each application is packaged in a container, and managing container deployment is equivalent to managing application deployment.

• Continuous integration and deployment: Containers eliminate environmental differences and ensure application life cycle environment consistency and standardization. Developers use images to build standard development environments. After development is completed, the complete environment and application images are packaged. Test and operation personnel can directly deploy the images for testing and release, simplifying the continuous integration, testing and release processes.

• Environment standardization and version control: Based on the environmental consistency and standardization provided by the container, the container image can be version controlled, that is, the entire operating environment can be version controlled, providing reliable and frequent Container image building, deployment and rollback are fast and easy.

• Efficient resource utilization and isolation: Containers have no additional overhead of hypervisors and share the operating system with the underlying layer. They have excellent performance and low system load. They can run more application instances under the same conditions. Make full use of system resources. Containers also have good resource isolation and control capabilities, and can accurately allocate system resources to ensure that applications do not affect each other.

• Observable: Not only displays information and metrics from the operating system, but also from the application itself.

• Cloud and OS distribution portability: Runs on Ubuntu, RHEL, CoreOS, physical machines, GKE and anywhere else.

• Application-centric: From deploying operating systems on traditional hardware to deploying applications in the operating system.

• Loosely coupled, distributed, elastic and microservices: applications are divided into smaller, more independent modules and can be managed and deployed dynamically rather than running on dedicated devices large single program.

What is Docker

Docker is undoubtedly the leader among many container technologies. As for what Docker is, we can summarize it through the following points:

Docker is an open source container project. The code is maintained on GitHub and follows Apache 2.0 protocol and has joined the Linux Foundation. It is supported by mainstream operating systems and cloud service providers, and has established and promoted the Open Container Alliance (OCI).

Docker uses Google's Go language for development and implementation. Based on the Linux kernel's namespace (namespace), control group (cgroup) and Union FS of the OverlayFS class, it encapsulates and isolates the process and belongs to the operating system. level of virtualization technology. Because the isolated process is independent of the host and other isolated processes, it is also called a container.

Docker was originally implemented based on Linux container (LXC), and later replaced LXC with its own developed libcontainer, and then further evolved to use runc and containerd.

Docker provides an efficient, agile and lightweight container solution that can quickly and automatically deploy applications within the container. It provides resource isolation and security for the container through operating system kernel technology, greatly simplifying container creation and Maintain and support deployment to on-premises environments and multiple cloud platforms. In other words, Docker provides a one-stop solution for application development, running and deployment.

runc is a Linux command line tool used to create and run containers according to the OCI container runtime specification.

containerd is a daemon that manages the container life cycle and provides a minimal set of functions for executing containers and managing images on a node.

Advantages of Docker

As an emerging virtualization method, Docker has many advantages compared with traditional virtualization methods. The specific summary is as follows:

• More efficient use of system resources: Containers do not require additional overhead such as hardware virtualization and running a complete operating system. Docker has a higher utilization rate of system resources and a higher demand. Being smaller allows for higher performance. A host with the same configuration can run a larger number of applications using containers than virtual machines.

• Faster startup time: Docker container applications can achieve startup times of seconds or even milliseconds. This greatly saves development, testing, and deployment time.

• Consistent running environment: The Docker image provides a complete runtime environment except the kernel, ensuring the consistency of the application running environment, so that the same code will no longer be lost in another environment. Run this type of problem.

• Continuous delivery and deployment: Using Docker, you can achieve continuous integration, continuous delivery, and deployment by customizing application images. Developers build images through Dockerfile and perform integration testing with the continuous integration system. Operations and maintenance personnel can quickly deploy the image directly in the production environment, or even use it with the continuous deployment system for automatic deployment.

• Easier migration: Docker ensures the consistency of the execution environment, making it easier to migrate applications between different platforms without worrying about changes in the running environment causing the application to not run properly. Case.

• Easier maintenance and expansion: The layered storage and mirroring technology used by Docker makes it easier to reuse repeated parts of the application, and also makes the maintenance and update of the application simpler. It is also very simple to further extend the image based on the base image. Docker also maintains a large number of high-quality official images, further reducing the cost of image production for application services.

• Good isolation: Docker provides reliable resource isolation and security guarantee for containers, allowing containers to accurately allocate system resources and ensure that applications do not affect each other.

• Elastic Scaling: Good at handling concentrated bursts of server usage pressure and dynamically managing applications.

Recommended learning: "docker video tutorial"

The above is the detailed content of Is docker a container?. For more information, please follow other related articles on the PHP Chinese website!