Pod is the atomic unit of scheduler in K8s. Pods contains one or more containers, at least one. K8s(kubelet) will instantiate pods. Pod is running as long the container inside is running. Life cycle of pod – Pending, Running, Succeded/ Failed Pods will communicate with each other through a pod network – inter pod communication. If the pods are in same node, it will communicate via localhost. We can’t get the same pod again. We can get the similar pod.

kubelet – This is the main K8s agent. It inistantiates the pods in the node. It helps to register nodes with cluster. Its always watch the api server. kube-proxy – Its support for K8s networking. It provide ip address for the pods. Each pods inside a node will have same ip address. kube-proxy rules All pods communicate with each other on all nodes. All nodes communicate with all pods No network address translation – NAT pod – It is an

API server – It contains all the APIs provided by K8s. It acts as the front-end, we access via REST. It is like ears in human body, it receive the things. Cluster store – All the requests / data stored in cluster store. etcd is the storage unit use by k8s. It is like brain in human body. There is only one cluster store in a master. Controller Manager – It is manager of all the controllers. One controller is

K8s can manage the scalability challenge bring by containers. K8s runs many containers as a cluster K8s is a container orchestrator K8s provide the desired state – we desired to have 1000 containers K8s is self maintaining – self healing Auto rollback Auto scaling K8s managing load balancing K8s absorb changes K8s provide very speed deployment K8s enhance the productivity by reducing the dependency K8s provide the security improvement

Union mount is a type of a filesystem that can create an illusion of merging contents of several directories into one without modifying its original (physical) sources. Union mount or union filesystem is not the filesystem type, but rather a concept with many implementations. UnionFS, aufs, OverlayFS, ZFS, and Btrfs are different implementations of union file systems. Docker only needs to create thin layer on top of the image and rest of it can be shared between all the containers.

A Docker image is built up from a series of layers. Each layer represents an instruction in the image’s Dockerfile. All layers except the last one is read-only. To identify each layer separately, Layers are now identified by a digest, which takes the form algorithm:hex; for example: sha256:fc92eec5cac70b0c324cec2933cd7db1c0eae7c9e2649e42d02e77eb6da0d15f The hex element is calculated by applying the algorithm (SHA256) to a layer’s content. If the content changes, then the computed digest will also change. The image ID is also a digest,

overlay2 / overlay – default storage driver for all linux flavors aufs – AUFS is a union filesystem, which means it presents multiple directories called branches, in AUFS as a single directory on a single Linux host. These directories are known as layers in Docker. devicemapper – It is a block storage driver that stores data in blocks. btrfs – Only supported on SLES machine zfs – a next-generation filesystem that has many features like volume management, snapshots, checksumming, compression

FROM – Mention a docker image name. Ex: FROM ubuntu MAINTAINER – Mention about the author who create the docker file. Ex: MAINTAINER BittoKC RUN – To execute any command on the container. Ex: RUN touch /tmp/file1.txt ARG – To set an environment variable. Ex: ARG USER1 gehc_security EXPOSE – To specify about the network port that container use at runtime. Ex: EXPOSE 80 COPY – To copy files/directories within the file system of docker. Ex: COPY /tmp/file1.txt . ADD

Collection of file systems, ROOTFS, APPFS, USERFS. One copy of docker image can attach to many containers. From one image multiple containers can be created File system layered over each other. Higher layer wins. Each layer is each File system Layer 0 should be base image or Root FS Once image is attached to container, these layers will be attached to the container as a single layer The layers in the image will be in read only format, and to

The wait command will wait until a container stop, then print their exit codes.How to check:Start a containerdocker run –name bitto httpdRun docker waitdocker wait bittoKill the container from another terminal and check the return value in actual terminaldocker kill bitto

“docker update” command dynamically updates container configuration.Using this command we can restrict the usage of too many resources by a container.Example : docker update –kernel-memory 50M ad5f8182d65e –> Update kernel memory while the container is running

We can successfully execute the command docket pause only if the docker container is in running state. We can successfully execute the command docket unpause only if the docker container is in paused state. I think internally its deallocating (during pause) and reallocating (during pause) the resources.

docker stop It is stopping a running docker container. It is a graceful termination of docker container with exit code – Exited (0) docker kill It is killing a running docker container. It is a forceful termination of docker container with exit code – Exited (137)

Docker container image is a light weight and independent application run time environment.It is a collection of users attached with at least 1 root file system, 1 pid and 1 network.