Debug School: aswinp.achutham90@gmail.com

Write a self notes which cover all the list of resources which you learnt in this session with 1 liner explanation

aswinp.achutham90@gmail.com — Fri, 11 Nov 2022 05:49:00 +0000

Below are the list of resources covered:

POD - Used to create a POD which will host the container in the node.
Replication controller - Used to replicate PODs based on desired number of replicas.
Deployment - Deployment includes Replication Controller along with Versioning , rollback and rollout options.
Services - Services is used to Load balance the traffic between multple nodes based on the selector labels.
NOdePort - Nodeport exposes the port on the Node and forwards it to the respective services.
PV - Used by kubernetes cluster administrator to provision storage volumes for the cluster.
PVC - PVC is used by app team to claim storage for the POD from the PV. These are then mounted to the container using Volume MOunts.
Configmap - Used to store configuration details as key value pairs which is required by container. These are stored in cluster storage.
Secret - Secret are stored in encoded format. They are also stored as key value pairs in cluster storage.
Job - Used to run a command or a job in a container. This resource is killed after the job is completed.
Cronjob - Used to run a command or a job in a cron schedule in a container. This resource will keep running as per the cron schedule.
Daemontset
StatefulSet

What is POD?

aswinp.achutham90@gmail.com — Wed, 09 Nov 2022 07:45:36 +0000

POD are atomic entities in kubernetes and is used as a wrapper around the containers separating them from the rest. PODS can host multiple containers listening on different ports as main contaners and side car containers. All resources in the PODS are shared by the containers within the pods. Scheduler deploys resources and containers in a POD.

How Kubernetes works?All components and roles of their components

aswinp.achutham90@gmail.com — Wed, 09 Nov 2022 07:38:45 +0000

A kubernetes cluster contains master nodes and few worker nodes.
Worker nodes hosts the containers/pods and master nodes distributes the workloads to the worker nodes.
To achieve this behavior several components needs to be installed in Master nodes and Worker Nodes.
Components in Master Node:

apiserver: Api server is used to establish any communication with the kubernetes cluster through REST APIs. Any input to kuberenets cluster is received in JSONs.
Cluster storage: Its used to store all configuratons and state information of the cluster. It uses etcd to store the data. apiserver will connect with cluster store to fetch these informations.
Kube Contoller manager- It runs in infinite loop and watches for any changes in the cluster. Status is collected and shared with apiserver thus ensuring apiserver has the latest status. Each component in the cluster has a separate controller. Eg: Node, Endpoint, Namespace etc.
Kube scheduler - It watches apiserver for any new pods and schedules them in the available nodes.

Components in Worker Nodes:

Kubelet: It's an agent deployed in worker nodes and communicates with master node through apiserver. Kubelet instantiates pods in the nodes. Any nodes to be added to cluster requires kubelet to be setup.
Container Engine: Container engine is used for Container management like pulling images and starting and stopping containers. 3.Kube Proxy: Kube-proxy handles all networking requirements including load balancing across all pods, POD IP addresses.

Why we need Kubernetes?

aswinp.achutham90@gmail.com — Wed, 09 Nov 2022 07:19:30 +0000

Kubernetes provides several benefits over traditional infrastructure deployment:

Faster deployment: Applications can be deployed in a matter of seconds.
Any updates in the code can be moved to the infrastructure quickly updating the container image.
Disaster recovery is quicker, i.e. in case any nodes are unavailable kuberentes immediately detects the failure and builds up new containers in other working nodes.
Provides an abstraction to underlying implementations through apiserver calls.

What is Kubernetes?

aswinp.achutham90@gmail.com — Wed, 09 Nov 2022 07:12:49 +0000

Kubernetes is a container orchestration tool.
Containers provides challenges with respect to scalability across multiple hosts. Kubernetes helps to manage multiple docker hosts and load balance between multiple containers with in the same host thus overcoming the network limitations associated with docker scalability.
It helps to deploy the containers in your Infrastructure.
It also helps to provide the necessary resources required to run the container.

USING 2 ENTRYPOINT Commands in dockerfile

aswinp.achutham90@gmail.com — Tue, 08 Nov 2022 12:36:07 +0000

When you use 2 entrypoint commands the last entrypoint command will be considered.
Eg:

Write docekrfile with 2 entrypoint commands:
FROM ubuntu
MAINTAINER Rajesh Kumar << rajesh@scmgalaxy.com>>
ENV DEBIAN_FRONTEND=noninteractive
RUN apt-get update
RUN apt-get -y install tzdata
RUN apt-get install git -y && apt-get install -yq apache2
CMD echo "Hello world"
ENTRYPOINT ["/bin/echo", "Hello"]
ENTRYPOINT ["ls"]
Build the docker image using docker file

[root@localhost docs]# docker build -t aswin10 -f doc7 .
Sending build context to Docker daemon 9.728kB
Step 1/9 : FROM ubuntu
---> a8780b506fa4
Step 2/9 : MAINTAINER Rajesh Kumar << rajesh@scmgalaxy.com>>
---> Using cache
---> 88f6b6acfa81
Step 3/9 : ENV DEBIAN_FRONTEND=noninteractive
---> Using cache
---> c8a76e7a5f98
Step 4/9 : RUN apt-get update
---> Using cache
---> 4d9fe31bf152
Step 5/9 : RUN apt-get -y install tzdata
---> Using cache
---> 41891c047aab
Step 6/9 : RUN apt-get install git -y && apt-get install -yq apache2
---> Using cache
---> cfaefb036054
Step 7/9 : CMD echo "Hello world"
---> Using cache
---> e3a33016f8d3
Step 8/9 : ENTRYPOINT ["/bin/echo", "Hello"]
---> Using cache
---> a2eacdc1de3e
Step 9/9 : ENTRYPOINT ["ls"]
---> Running in 12768c86a79f
Removing intermediate container 12768c86a79f
---> 376e50f8e2e0
Successfully built 376e50f8e2e0
Successfully tagged aswin10:latest
[root@localhost docs]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
aswin10 latest 376e50f8e2e0 11 seconds ago 252MB

Creating the container using the run command: [root@localhost docs]# docker run -itd aswin10 e908ee7c1647d28048b5bb693e6c590b671ea93d72968cad4c15445e2bcda108 [root@localhost docs]# docekr ps -a bash: docekr: command not found... Similar command is: 'docker' [root@localhost docs]# docker ps -a CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES e908ee7c1647 aswin10 "ls /bin/sh -c 'echo…" 8 seconds ago Exited (2) 7 seconds ago eager_torvalds

Using 2 CMD commands in dockerfile

aswinp.achutham90@gmail.com — Tue, 08 Nov 2022 12:32:36 +0000

When you use 2 CMD commands in docker file the last CMD command will be considered.
eg:

Write dockerfile with 2 CMD commands:

FROM ubuntu
MAINTAINER Rajesh Kumar << rajesh@scmgalaxy.com>>
ENV DEBIAN_FRONTEND=noninteractive
RUN apt-get update
RUN apt-get -y install tzdata
RUN apt-get install git -y && apt-get install -yq apache2
CMD echo "Hello world"
CMD ls

Building the dockerfile:
[root@localhost docs]# docker build -t aswin1 -f doc38 .
unable to prepare context: unable to evaluate symlinks in Dockerfile path: lstat /root/docs/doc38: no such file or directory
[root@localhost docs]# docker build -t aswin1 -f doc8 .
Sending build context to Docker daemon 10.75kB
Step 1/8 : FROM ubuntu
---> a8780b506fa4
Step 2/8 : MAINTAINER Rajesh Kumar << rajesh@scmgalaxy.com>>
---> Using cache
---> 88f6b6acfa81
Step 3/8 : ENV DEBIAN_FRONTEND=noninteractive
---> Using cache
---> c8a76e7a5f98
Step 4/8 : RUN apt-get update
---> Using cache
---> 4d9fe31bf152
Step 5/8 : RUN apt-get -y install tzdata
---> Using cache
---> 41891c047aab
Step 6/8 : RUN apt-get install git -y && apt-get install -yq apache2
---> Using cache
---> cfaefb036054
Step 7/8 : CMD echo "Hello world"
---> Using cache
---> e3a33016f8d3
Step 8/8 : CMD ls
---> Running in 39af03f7ea29
Removing intermediate container 39af03f7ea29
---> 4ec90f2ffbdf
Successfully built 4ec90f2ffbdf
Successfully tagged aswin1:latest
[root@localhost docs]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
aswin1 latest 4ec90f2ffbdf 10 seconds ago 252MB
Running docker run command to create the container:
[root@localhost docs]# docker run -itd aswin1
837cffa37f38494cfdc264bb5da82b4f515834d850f2b23b822971230fe03022
[root@localhost docs]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
837cffa37f38 aswin1 "/bin/sh -c ls" 7 seconds ago Exited (0) 6 seconds ago keen_wright

Diff between docker pause and docker unpause?

aswinp.achutham90@gmail.com — Mon, 07 Nov 2022 13:14:24 +0000

Docker pause freezes all running processesin the container.

EG:
Docker pause:
[root@localhost CONTAINER ID IMAGE 79d6e4829aa7 httpd 2e41b8634ec5 [root@localhost aswin [root@localhost bin]# docker ps -a CONTAINER ID IMAGE 79d6e4829aa7 httpd 2e41b8634ec5 [root@localhost bin]# docker stats CONTAINER ID NAME 79d6e4829aa7 aswin CONTAINER ID NAME 79d6e4829aa7 aswin CONTAINER ID NAME 79d6e4829aa7 aswin CONTAINER ID NAME 79d6e4829aa7 aswinDocker [root@localhost aswin
[root@localhost bin]# docker ps -a
CONTAINER ID IMAGE 79d6e4829aa7 httpd 2e41b8634ec5 [root@localhost bin]# docker stats
CONTAINER ID NAME 79d6e4829aa7 aswin CONTAINER ID NAME 79d6e4829aa7 aswin CONTAINER ID NAME 79d6e4829aa7 aswin CONTAINER ID NAME 79d6e4829aa7 aswin CONTAINER ID NAME 79d6e4829aa7 aswin CONTAINER ID NAME 79d6e4829aa7 aswin bin]# docker ps -a
COMMAND CREATED STATUS PORTS NAMES
"httpd-foreground" 31 seconds ago Up 3 seconds 80/tcp aswin
hello-world "/hello" 3 hours ago Exited (0) 3 hours ago inspiring_hugle
bin]# docker pause aswin
COMMAND CREATED STATUS PORTS NAMES
"httpd-foreground" 45 seconds ago Up 17 seconds (Paused) 80/tcp aswin
hello-world "/hello" 3 hours ago Exited (0) 3 hours ago inspiring_hugle
CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
0.00% 8.785MiB / 3.701GiB 0.23% 656B / 0B 0B / 0B 82
CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
0.00% 8.785MiB / 3.701GiB 0.23% 656B / 0B 0B / 0B 82
CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
0.00% 8.785MiB / 3.701GiB 0.23% 656B / 0B 0B / 0B 82
CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
0.00% 8.785MiB / 3.701GiB 0.23% 656B / 0B 0B / 0B 82
Unpause
bin]# docker unpause aswin
COMMAND CREATED STATUS PORTS NAMES
"httpd-foreground" 4 minutes ago Up 3 minutes 80/tcp aswin
hello-world "/hello" 3 hours ago Exited (0) 3 hours ago inspiring_hugle
CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
0.00% 8.785MiB / 3.701GiB 0.23% 656B / 0B 0B / 0B 82
CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
0.00% 8.785MiB / 3.701GiB 0.23% 656B / 0B 0B / 0B 82
CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
0.01% 8.785MiB / 3.701GiB 0.23% 656B / 0B 0B / 0B 82
CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
0.01% 8.785MiB / 3.701GiB 0.23% 656B / 0B 0B / 0B 82
CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
0.01% 8.785MiB / 3.701GiB 0.23% 656B / 0B 0B / 0B 82
CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
0.01% 8.785MiB / 3.701GiB 0.23% 656B / 0B 0B / 0B 82

Docker wait command

aswinp.achutham90@gmail.com — Mon, 07 Nov 2022 12:57:07 +0000

Docker wait command waits till the container stops and returns the exit codes.

Eg:

Start a container in terminal 1.
[root@localhost /]# docker run -dit --name=my_container ubuntu bash
6eeb1f587cebdb3c4e9c071b4794a25f17c41c7afa4b1119967eb9d0775875f1
[root@localhost /]# docker wait my_container
In another terminal stop the container my_container created in terminal1.
[root@localhost ~]# docker stop my_container
my_container
In terminal 1 you will notice the wait command returns the exit code:
[root@localhost /]# docker wait my_container
137

Update configuration of one or more containers

aswinp.achutham90@gmail.com — Mon, 07 Nov 2022 12:43:16 +0000

Docker update dynamically updates docker configurations.

Eg:

CPU Shares before update:
[root@localhost /]# docker inspect edd512ee70b7
[
.
.
.
.
"CpuShares": 512,
"Memory": 0,
Docker update performed on container edd512ee70b7

[root@localhost /]# docker update --cpu-shares 256 edd512ee70b7
edd512ee70b7
CPU shares after update:
[root@localhost /]# docker inspect edd512ee70b7
"Dns": [],
"DnsOptions": [],
"DnsSearch": [],
"ExtraHosts": null,
"GroupAdd": null,
"IpcMode": "private",
"Cgroup": "",
"Links": null,
"OomScoreAdj": 0,
"PidMode": "",
"Privileged": false,
"PublishAllPorts": false,
"ReadonlyRootfs": false,
"SecurityOpt": null,
"UTSMode": "",
"UsernsMode": "",
"ShmSize": 67108864,
"Runtime": "runc",
"ConsoleSize": [
0,
0
],
"Isolation": "",
"CpuShares": 256,

Diff between docker stop and docker kill?

aswinp.achutham90@gmail.com — Mon, 07 Nov 2022 10:39:58 +0000

The docker stop command stops the container gracefully and provides a safe way out. If a docker stop command fails to terminate a process within the specified timeout, the Docker issues a kill command implicitly and immediately.
The docker kill command terminates the entry point process abruptly. The docker kill command causes an unsafe exit

docker kill:
`[root@localhost bin]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
16a5ba925596 httpd "httpd-foreground" 8 minutes ago Up 7 minutes 80/tcp aswin2
5c8327c8ce40 httpd "httpd-foreground" 8 minutes ago Up 2 minutes 80/tcp aswin1
2e41b8634ec5 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago inspiring_hugle
[root@localhost bin]# docker kill aswin1
aswin1
[root@localhost bin]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
16a5ba925596 httpd "httpd-foreground" 8 minutes ago Up 7 minutes 80/tcp aswin2
5c8327c8ce40 httpd "httpd-foreground" 9 minutes ago Exited (137) 3 seconds ago aswin1

docker stop:

[root@localhost bin]# docker ps -a CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 16a5ba925596 httpd "httpd-foreground" 3 minutes ago Up 2 minutes 80/tcp aswin2 5c8327c8ce40 httpd "httpd-foreground" 3 minutes ago Up 53 seconds 80/tcp aswin1 2e41b8634ec5 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago inspiring_hugle [root@localhost bin]# docker stop aswin1 aswin1 [root@localhost bin]# docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 16a5ba925596 httpd "httpd-foreground" 3 minutes ago Up 2 minutes 80/tcp aswin2

2e41b8634ec5 hello-world "/hello" 3 hours ago Exited (0) 3 hours ago inspiring_hugle`