Docker is a set of platform as a service product that use OS-level virtualization to deliver software in packages called containers. Containers are isolated from one another and bundle their own software, libraries and configuration files; they can communicate with each other through well-defined channels.
Docker provides the ability to package and run an application in a loosely isolated environment called a container. The isolation and security allow you to run many containers simultaneously on a given host.
Docker architecture
Docker uses a client-server architecture. The Docker client talks to the Docker daemon, which does the heavy lifting of building, running, and distributing your Docker containers. The Docker client and daemon can run on the same system, or you can connect a Docker client to a remote Docker daemon. The Docker client and daemon communicate using a REST API, over UNIX sockets or a network interface.
The Docker daemon
The Docker daemon (dockerd) listens for Docker API requests and manages Docker objects such as images, containers, networks, and volumes. A daemon can also communicate with other daemons to manage Docker services.
The Docker client
The Docker client (docker) is the primary way that many Docker users interact with Docker. When you use commands such as docker run, the client sends these commands to dockerd, which carries them out. The docker command uses the Docker API. The Docker client can communicate with more than one daemon.
Docker registries
A Docker registry stores Docker images. Docker Hub is a public registry that anyone can use, and Docker is configured to look for images on Docker Hub by default. You can even run your own private registry.
When you use the docker pull or docker run commands, the required images are pulled from your configured registry. When you use the docker push command, your image is pushed to your configured registry.
SERVICES
Services allow you to scale containers across multiple Docker daemons, which all work together as a swarm with multiple managers and workers. Each member of a swarm is a Docker daemon, and all the daemons communicate using the Docker API. A service allows you to define the desired state, such as the number of replicas of the service that must be available at any given time. By default, the service is load-balanced across all worker nodes.
Namespaces
Docker uses a technology called namespaces to provide the isolated workspace called the container. When you run a container, Docker creates a set of namespaces for that container.
These namespaces provide a layer of isolation.
Control groups
Docker Engine on Linux also relies on another technology called control groups (cgroups). A cgroup limits an application to a specific set of resources.
Docker Engine is a client-server application with these major components:
- A server which is a type of long-running program called a daemon process (the
dockerdcommand). - A REST API which specifies interfaces that programs can use to talk to the daemon and instruct it what to do.
- A command line interface (CLI) client (the
dockercommand).
How Does Docker Works?
Docker works on a client-server architecture. It includes the docker client, docker host, and docker registry. The docker client is used for triggering docker commands, docker host is used to running the docker daemon, and docker registry to store docker images.
The docker client communicates to docker daemon using a REST API, which internally supports to build, run, and distribute docker containers. Both the client and daemon can run on the same system or can be connected remotely.
References:
- https://docs.docker.com
- from Miscellaneous technical websites.