Introduction to Docker and Kubernetes - madhusudana30/Kubernetes-Learning GitHub Wiki

Install Docker in Linux and Run the Daemon

sudo su

yum install docker

service docker start

Docker Fundamentals

Docker runs on Container based Management.
Docker Client -Server Architecture:
Docker Client - command line interacts with Docker Daemon.
Docker Client GUI- Kitematic
Run docker container in background:
docker run -d imagename
list all docker runs and background docker
docker ps -a
Name docker:
docker run -name hello image name
docker inspect dockerimageid (backgorund id)

Docker Port mapping and logs Command:

docker run -it -p 8888:8080 tomcat:8.0
ctl + c to exit
docker logs dockerId: To see the logs.

Docker Image:

docker history dockerimage:tag

Build Docker Images:

Docker File is a text document that contains instructions to assemble image.

Create docker file:

touch Dockerfile (Name should be Dockerfile without any extention)

if docker file is in different location provide -f option while building an image.

Build Docker Image:

docker build -t name/imageName . (. specifies Dockerfile is available in current directory)
Docker Images are persistent and read only

Ways to Build Docker Image:

Commit changes made in docker container
Write a Dockerfile.
Docker commit saves changes made in Docker Container and creates a new Image.
get docker container id
docker ps -a
docker commit containerId userName/imagename:version
creates a new image and returns the container id.
spin of container with new image.
Try with the Debian image to build openldap

Dockerfile in Depth:

Each run command will execute the command on the top writable layer of the conainer and then commit the container as a new image.
The New image is used as a next step in Dockerfile. So each run instruction creates a new image layer.
Its Recommended the chain the run instructions in Dockerfile to reduce the number of image layers it creates.
Aggregate the number of instructions in single Run command in Dockerfile.

RUN apt-get update && apt-get install

Sort multi line arguments for readability.

CMD comamnds

CMD instruction specifies what command to run during the start up of Docker container.

CMD ["echo","hello-world"]

Docker build and run to see message.
Override the CMD instruction while running docker container.

Docker Cache:

Each time docker executes an instruction it builds a new image layer.
If there is no change in instruction, next time Docker executes an instruction it reuses the image layer. ** Specify No Cache Instruction** --no-cache=true to avoid caching.

Copy Instructions

Copy instruction copies files or Directories from build context and adds them to the file system of Docker Container.
touch abc.txt
vi Dockerfile
COPY abc.txt /src/abc.txt
docker build -t username/imagename .
successfully build image id:
docker run -t image id to enter into docker file system of container.
cd src
ls
ADD instruction is similar to COPY but ADD can download from internet and unpack compressed files.

PUSH Docker Image to Docker hub

https://hub.docker.com
signup for docker hub account.

official images are preferred.

User always version instead of latest tag of image.
User docker hub credentials to push image to docker hub.

Containerize the Simple Web Application

*** see ip address of docker machine**

docker-machine ls

**Run commands inside the Running Docker container **

docker exec -t containerId bash(which command to run)
ps axu displays all running process in the container.

EXAMPLES:

yum install docker
service docker start
Create Docker File
vi Dockerfile
FROM centos:7
Build Docker Image:
docker build -t openldapimage .
[root@angularmachine Downloads]# docker build -t openldapimage .
Sending build context to Docker daemon 176.6 MB
Step 1/1 : FROM centos:7
Trying to pull repository docker.io/library/centos ...
7: Pulling from docker.io/library/centos
8ba884070f61: Pull complete
Digest: sha256:b5e66c4651870a1ad435cd75922fe2cb943c9e973a9673822d1414824a1d0475
Status: Downloaded newer image for docker.io/centos:7
---> 9f38484d220f
Successfully built 9f38484d220f
Start Docker image with bash command
it is for interactive mode
docker run -it 9f38484d220f bash
docker cp openldap-2.4.47 de588d2e6f74ff795ce15abd0e8e8826b2e4a70a332a9f04f923709222a46e07:/home/openldap-2.4.47
COPY Contents from/To Docker Container
https://stackoverflow.com/questions/22907231/copying-files-from-host-to-docker-container
The cp command can be used to copy files. One specific file can be copied like:
docker cp foo.txt mycontainer:/foo.txt
docker cp mycontainer:/foo.txt foo.txt
For emphasis, mycontainer is a container ID, not an image ID.
Multiple files contained by the folder src can be copied into the target folder using:
docker cp src/. mycontainer:/target
docker cp mycontainer:/src/. target
Reference: Docker CLI docs for cp
In Docker versions prior to 1.8 it was only possible to copy files from a container to the host. Not from the host to a container.
docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
128de889d173 9f38484d220f "bash" 2 minutes ago Exited (0) 2 minutes ago kickass_jones
de588d2e6f74 9f38484d220f "bash" 3 minutes ago Exited (0) 3 minutes ago elastic_clarke
26ed3e64b217 9f38484d220f "bash" 7 minutes ago Exited (130) 3 minutes ago pedantic_easley
bd54200017b4 9f38484d220f "/bin/bash" 7 minutes ago Up 7 minutes serene_joliot
903349c074ae 9f38484d220f "bash" 9 minutes ago Up 9 minutes lucid_engelbart
https://www.youtube.com/watch?v=7tGcnOvRQ9o
working cp:
docker run -it --name openldapimage 9f38484d220f /bin/bash
copy text file from docker image to current directory.
docker cp openldapimage:/home/test.txt .
Copy tar file from vm to docker image
docker cp openldap-2.4.47.tgz openldapimage:/home/
docker ps
docker start openldapimage
docker exec -it openldapimage /bin/bash