Debug School: varunakg

Learning in Kubernetes

varunakg — Fri, 11 Nov 2022 05:51:54 +0000

ETCD, Controller Manager, API Server, Scheduler, POD, Storage Class, Configmap, Secret, PV, PVC, Job, Cronjob, stateful, stateless

What is POD?

varunakg — Wed, 09 Nov 2022 07:36:50 +0000

A pod is the smallest execution unit in Kubernetes. A pod encapsulates one or more applications. If a pod (or the node it executes on) fails, Kubernetes can automatically create a new replica of that pod to continue operations.
When pods contain multiple containers, communications, and data sharing between them is simplified. Since all containers in a pod share the same network namespace, they can locate each other and communicate via localhost. Pods can communicate with each other by using another pods IP address or by referencing a resource that resides in another pod.
Pods can include containers that run when the pod is started, say to perform initiation required before the application containers run. Additionally, pods simplify scalability, enabling replica pods to be created and shut down automatically based on changes in demand.

How Kubernetes works?All components and roles of their components

varunakg — Wed, 09 Nov 2022 07:32:24 +0000

Kubernetes is a system that manages containers (containerized applications) where a container could be explained as a lightweight virtual machine. To build an application you need to build a bunch of containers and then use Kubernetes to manage those containers.

A Kubernetes cluster has two main components—the control plane and data plane, machines used as compute resources :
-The control plane hosts the components used to manage the Kubernetes cluster.
-Worker nodes can be virtual machines (VMs) or physical machines. A node hosts pods, which run one or more containers.

Here are the main components of the control plane:

kube-apiserver : Provides an API that serves as the front end of a Kubernetes control plane. It is responsible for handling external and internal requests—determining whether a request is valid and then processing it.
kube-scheduler : This component is responsible for scheduling pods on specific nodes according to automated workflows and user defined conditions, which can include resource requests, concerns like affinity and taints or tolerations, priority, persistent volumes (PV), and more.
kube-controller-manager : The controller manager is responsible for several controllers that handle various automated activities at the cluster or pod level, including replication controller, namespace controller, service accounts controller, deployment, statefulset, and daemonset.
etcd : A key-value database that contains data about your cluster state and configuration. Etcd is fault tolerant and distributed.
cloud-controller-manager : It enables you to connect a Kubernetes cluster with the API of a cloud provider.

Here are the main components of the Worker nodes:

Nodes : Nodes are physical or virtual machines that can run pods as part of a Kubernetes cluster.
Pods : A pod serves as a single application instance, and is considered the smallest unit in the object model of Kubernetes.
Container Runtime Engine : Each node comes with a container runtime engine, which is responsible for running containers.
kubelet : Each node contains a kubelet, which is a small application that can communicate with the Kubernetes control plane.
kube-proxy : All compute nodes contain kube-proxy, a network proxy that facilitates Kubernetes networking services.
Container Networking : Container networking enables containers to communicate with hosts or other containers.

Why we need Kubernetes?

varunakg — Wed, 09 Nov 2022 07:15:37 +0000

Container orchestration savings.
Increased DevOps efficiency for microservices architecture.
Deploying workloads in multicloud environments.
More portability with less chance of vendor lock-in.
Automation of deployment and scalability.
App stability and availability in a cloud environment.
Open-source benefits of Kubernetes.
Free Cloud Solution.
Architectural advantages. 10.Simplified DevOps and performance.

Q1. What is Kubernetes?

varunakg — Wed, 09 Nov 2022 07:09:07 +0000

1-Kubernetes is a system that manages containers where a container could be explained as a lightweight virtual machine.
2-To build an application you need to build a bunch of containers and then use Kubernetes to manage those containers.
3-This sounds like something very difficult and time-consuming, but the advantage is that Kubernetes can create and scale containers automatically and manage storage among all the containers.
4-Kubernetes does load balancing when there is too much traffic.
5-Kubernetes helps you do some storage stuff with a disc.
6-Kubernetes eliminates many of the manual processes involved in deploying and scaling containerized applications and standardizes them.
7-Kubernetes orchestration allows you to build application services that span multiple containers, schedule containers across a cluster, scale those containers, and manage their health over time.
8-Kubernetes High-Availability is another benefit because if something fails, it will replace it and restart over.

wait Block until one or more containers stop, then print their exit codes

varunakg — Mon, 07 Nov 2022 13:30:15 +0000

Answer :

update Update configuration of one or more containers

varunakg — Mon, 07 Nov 2022 13:07:51 +0000

[root@localhost ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
a629508cfe3e httpd "httpd-foreground" 2 hours ago Up 2 hours 80/tcp elastic_lederberg
94eb9f15fa12 httpd "httpd-foreground" 2 hours ago Up 2 hours 0.0.0.0:81->80/tcp, :::81->80/tcp angry_merkle
b05697f3d130 httpd "httpd-foreground" 2 hours ago Up 2 hours 0.0.0.0:80->80/tcp, :::80->80/tcp vigilant_jepsen
d8c997ec449e httpd "httpd-foreground" 2 hours ago Up 2 hours 80/tcp xenodochial_lederberg
b32155889703 httpd "httpd-foreground" 3 hours ago Created vj2
d9362521b23b httpd "httpd-foreground" 3 hours ago Created agitated_jackson
b14acb2bfc36 hello-world "/hello" 6 hours ago Exited (0) 6 hours ago awesome_zhukovsky
693a7fc72262 hello-world "/hello" 6 hours ago Exited (0) 6 hours ago quirky_wiles
[root@localhost ~]# docker update --restart=on-failure:3 b32155889703 vj2
b32155889703
vj2

Diff between docker pause and docker unpause?

varunakg — Mon, 07 Nov 2022 12:59:11 +0000

Answer : Pause means that the processes in the container stop running and they are be able to be resumed later. Unpause resumes all the processes in the specified container.

[root@localhost ~]# docker pause vj1
vj1
[root@localhost ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
b32155889703 httpd "httpd-foreground" 2 minutes ago Created vj2
15321b2e4b20 httpd "httpd-foreground" 3 minutes ago Up 35 seconds (Paused) 80/tcp vj1
d9362521b23b httpd "httpd-foreground" 4 minutes ago Created agitated_jackson
b14acb2bfc36 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago awesome_zhukovsky
693a7fc72262 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago quirky_wiles
[root@localhost ~]# docker unpause vj1
vj1
[root@localhost ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
b32155889703 httpd "httpd-foreground" 3 minutes ago Created vj2
15321b2e4b20 httpd "httpd-foreground" 3 minutes ago Up 52 seconds 80/tcp vj1
d9362521b23b httpd "httpd-foreground" 5 minutes ago Created agitated_jackson
b14acb2bfc36 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago awesome_zhukovsky
693a7fc72262 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago quirky_wiles

Diff between docker stop and docker kill?

varunakg — Mon, 07 Nov 2022 12:41:41 +0000

Answer : Stop attempts to trigger a graceful shutdown by sending the standard POSIX signal whereas kill just kills the process by default.

[root@localhost ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
b32155889703 httpd "httpd-foreground" About a minute ago Created vj2
15321b2e4b20 httpd "httpd-foreground" 2 minutes ago Exited (0) 5 seconds ago vj1
d9362521b23b httpd "httpd-foreground" 3 minutes ago Created agitated_jackson
b14acb2bfc36 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago awesome_zhukovsky
693a7fc72262 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago quirky_wiles
[root@localhost ~]# docker start vj1
vj1
[root@localhost ~]# docker stop vj1
vj1
[root@localhost ~]# docker start vj1
vj1
[root@localhost ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
b32155889703 httpd "httpd-foreground" 2 minutes ago Created vj2
15321b2e4b20 httpd "httpd-foreground" 2 minutes ago Up 6 seconds 80/tcp vj1
d9362521b23b httpd "httpd-foreground" 3 minutes ago Created agitated_jackson
b14acb2bfc36 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago awesome_zhukovsky
693a7fc72262 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago quirky_wiles
[root@localhost ~]# docker kill vj1
vj1
[root@localhost ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
b32155889703 httpd "httpd-foreground" 3 minutes ago Created vj2
15321b2e4b20 httpd "httpd-foreground" 4 minutes ago Exited (137) 9 seconds ago vj1
d9362521b23b httpd "httpd-foreground" 5 minutes ago Created agitated_jackson
b14acb2bfc36 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago awesome_zhukovsky
693a7fc72262 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago quirky_wiles