API Server
Kubernetes is an API server which provides all the operation on cluster using the API.

Controller Manager
This component is responsible for most of the collectors that regulates the state of cluster and performs a task.

Scheduler
This is one of the key components of Kubernetes master. It is a service in master responsible for distributing the workload.

Kubernetes – Node Components
Following are the key components of Node server which are necessary to communicate with Kubernetes master.

Docker
The first requirement of each node is Docker which helps in running the encapsulated application containers in a relatively isolated but lightweight operating environment.

Kubelet Service
This is a small service in each node responsible for relaying information to and from control plane service. It interacts with etcd store to read configuration details and wright values.

Kubernetes Proxy Service
This is a proxy service which runs on each node and helps in making services available to the external host. It helps in forwarding the request to correct containers and is capable of performing primitive load balancing.

9) COPY : Copies new files or directories from and adds them to the filesystem of the image at the path .
eg : COPY –chown=55:mygroup files* /somedir/
10) ENTRYPOINT : Allows you to configure a container that will run as an executable.
eg : ENTRYPOINT [“/usr/sbin/apache2ctl”, “-D”, “FOREGROUND”]
11) VOLUME : Creates a mount point with the specified name and marks it as holding externally mounted volumes from native host or other containers.
eg: VOLUME /myvol
12) USER : The USER instruction sets the user name or UID to use when running the image and for any RUN, CMD and ENTRYPOINT instructions that follow it in the Dockerfile.
eg : USER mani
13 ) WORKDIR : Sets the working directory for any RUN, CMD, ENTRYPOINT, COPY, and ADD instructions that follow it.
eg: WORKDIR /export/home
14) ARG : Defines a variable that users can pass at build-time to the builder with the docker build command using the –build-arg = flag.
eg : ARG user1=mani.km

15) ONBUILD : Adds to the image a trigger instruction to be executed at a later time, when the image is used as the base for another build. The trigger will be executed in the context of the downstream build, as if it had been inserted immediately after the FROM instruction in the downstream Dockerfile.
eg : ONBUILD RUN /usr/local/bin/python-build –dir /app/src
16) STOPSIGNAL: instruction sets the system call signal that will be sent to the container to exit. This signal can be a valid unsigned number that matches a position in the kernel’s syscall table, for instance 9, or a signal name in the format SIGNAME, for instance SIGKILL.
eg : STOPSIGNAL signal
17) HEALTHCHECK : Tells Docker how to test a container to check that it is still working
eg: HEALTHCHECK –interval=5m –timeout=3s \
CMD curl -f http://localhost/ || exit 1
18) SHELL : Allows the default shell used for the shell form of commands to be overridden.
eg : SHELL [“powershell”, “-command”]

Docker image image is a file used to execute code in a Docker container.