What is Docker
Docker is developed by Google using the go language, encapsulating and isolating processes, starting with virtualization technology at the operating system level.
Because the isolated process is independent of the host and other isolated processes, it becomes a container
Docker has further encapsulated the container based on the container, from file system, network interconnection to process isolation, etc., simplifying the maintenance and bed frame of the container, which is lighter and faster than virtual machine technology.
Why use it
As an emerging virtualization method, it has many advantages over traditional ones
- More efficient use of system resources
Containers do not require additional overhead such as virtual hardware and a complete operating system, so they have higher resource utilization rates on the system. From the following aspects, application execution speed, memory loss, file storage speed, etc. are all funny than traditional virtual machines. Therefore, a host with the same configuration can run more applications
- Faster start time
Because the host kernel is directly run, the startup time can be achieved in seconds and milliseconds; save time
- A consistent operating environment
Docker's image provides a complete runtime environment except for the kernel, ensuring the consistency of the application running environment; [Development, testing, production environment]
- Continuous delivery and deployment
Continuous integration, delivery, and deployment through customized application images; mirror construction through Dockerfile; Dockerfile makes mirror construction transparent and easy to understand
- Easily migrate
Because the consistency of the environment is ensured, it is easy to migrate;
- Easily maintain and expand
Use hierarchical storage and mirroring technologies to make application reuse easier and maintenance and updates simpler.
Basic concepts
Understanding the following three concepts will make you understand the entire life cycle of Docker
Mirror
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The operating system is divided into kernel and user space; Docker image is equivalent to a root file system
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Docker image is a special file system. In addition to providing programs, libraries, resources, configuration and other files required for runtime, it also contains some configuration parameters. But does not contain any dynamic data
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Layered storage makes mirror reuse and customization easier
container
- The relationship between a container and a mirror is like a class or instance; the mirror is static, and the container is the entity that runs the mirror; the container can be created, started, stopped, deleted, suspended and other operations.
- A container is essentially a process, but it runs in its own independent space; so each container has its own root system, network configuration, process space, and even its own user ID space.
- Containers are also stored in layers. When each container runs, it uses the mirror as the basis layer to be the current storage layer; this container storage layer is prepared for container operation read and write.
- When the container dies, the storage layer will also disappear; so the information stored in the container storage layer will be missing.
- The container should not write data to the storage layer. All file writing operations require the use of data volumes or binding to the host directory; directly read and write the host and network storage, with high performance and stability.
- The life cycle of the data volume is independent container, the container disappears, and the data volume is still there
storehouse
- It is divided into public and private warehouses
- After the image is built, it needs to be published to the centralized storage and distribution mirror service.Docker Registry
- oneDocker RegistryIt can contain multiple Repository, each repository has multiple tags, each tag corresponds to a mirror
- Generally speaking, a warehouse will contain different versions of the same software, and the tag is used to label different versions;
- Can be passed
<warehouse name>:<tag>The format is to specify which version of the image of this software. If no tag is given, thelatestAs the default label