Docker Notes
Everything you need to run your first Container!
Let's know each other :)
Hi, I'm Jatin Shharma.
So I teach students and professionals these interesting
topics like:
Programming, Automation Testing and DevOps
If you too have the same interest feel free to connect
with me on Linked In
ah and my website: www.testautomationacademy.in
What is Docker
What is Docker
Docker is a platform for developers and sysadmins to develop, ship, and run applications by using containers.
host system host system
Docker Daemon Docker Daemon
Docker aids the user to test and deploy the code into production Quickly!
IMP
V Why use Docker ?
Docker helps in:
1 Application packaging
2 Process Isolation and Management
3 Multitenancy
4 Rapid Deployment
What is Application Packaging?
Docker helps you package applications and their dependencies into portable application images that are
straightforward to distribute to artifact repositories and then onto container hosts that will run them
host system host system
image Docker Engine Docker Engine
Docker Engine consist of server which a program which called as docker daemon
What is Process Isolation in Docker?
Docker’s container engine and command line tool make it simple to retrieve application images and start
isolated instances of each application process.
host system
Key terms to Remember
Docker’s container engine and command line tool make it simple to retrieve application images and start
isolated instances of each application process.
host system
Workflow to Containerize
any application
Workflow to Containerize any
application
builds
run
Read-only
template
docker container
docker image 2
Docker file 1
3
Workflow to Containerize any
application
2 docker build
3 docker run
dockerfile
1
Note: Here we are creating a dockerfile for nodejs application!
Basic Docker
Commands
IMP
V Basic Docker Commands
docker build : The docker build command builds Docker images from a
1 Dockerfile
2 docker pull : Pull an image or a repository from a registry
3 docker push: Push an image or a repository to a registry
4 docker ps : returns an overview of all running containers.
5 docker images : Shows the list of images
Basic Docker Commands
61 docker system prune: Remove unused data
2
7 docker kill : Kill one or more running containers
8 docker restart: Restart one or more containers
9 docker rm : Remove one or more containers
10 docker rmi : Remove one or more images
Basic Docker Commands
11
1 docker logs: Fetch the logs of a container
12
2 docker run :Run a command in a new container
13 docker login: Log in to a Docker registry
Let's package containerize our
application
Assignment:
Your company has decided to adopt the devops process for your current project and they wish to change
the way they are currently deploying the application on the server.
In past, the deployment was a very complex process because sometimes the developer system config and
server config were mismatched. Hence it used to take a lot of time to deploy the application to PROD and
find if the correct version has been deployed.
Instead of pulling the code from the remote repository, they want to deploy the docker image of the
application.
Your Job is to containerize the existing application. Push the image to docker hub and deploy it into the
cloud server.
PS make sure the image size is optimum.
Docker File
Instruction List
IMP
V Step1: Create Docker File
Docker File is text file that consist of all the instructions that are required a docker image.
Each instruction creates a docker layer in the image!
FROM ADD USER ONBUILD
RUN COPY VOLUME STOPSIGNAL
CMD EXPOSE WORKDIR ENTRYPOINT
LABEL ENV ARG HEALTHCHECK
INSTRUCTION LIST
FROM
FROM is used to begin a new build stage. This sets the base image for subsequent
instructions.
Syntax: FROM <image> [AS <name>]
Remember:
It's all ways the First instruction in DockerFile
FROM can be written multiple times to create images in a DockerFile.
name is the build stage in the Dockerfile!
INSTRUCTION LIST
Run
RUN instruction is used to execute a command inside a docker image!
Syntax: RUN [COMMAND]
Example: RUN yum update
Remember:
You can execute shell linux command or app command directly inside an
image with the help of Run instruction.
RUN instruction is used to executes any commands on top of the current image
and this will create a new layer
INSTRUCTION LIST
CMD
FROM is used to begin a new build stage. This sets the base image for subsequent
instructions.
Syntax: FROM <image> [AS <name>]
cmd java SampleJava.java cmd [“java ”,” SampleJava.java”]
INSTRUCTION LIST
CMD
Remember:
It's all ways the First instruction in DockerFile
FROM can be written multiple times to create images in a DockerFile.
name is the build stage in the Dockerfile!
INSTRUCTION LIST
LABEL
If you wish to add extra information or metadata information to the image you
can use LABEL instruction
Syntax: LABEL <key>=<value>
Remember:
A LABEL is a key-value pair.
Example:
label “application_environment”=”development”
INSTRUCTION LIST
ADD
ADD copies new directories, files, and URLs of remote files from src.
The is a path where the source is copied in the destination container.
Syntax: ADD [--chown=<user>:<group>] <src> .. <dest>
Example:
Shell Form – ADD src dest
add /root/testData /data/
INSTRUCTION LIST
COPY
The COPY copies new directories and files from source.
COPY also adds those new directories and files to the container’s filesystem
at the path <DEST>
Syntax: COPY [--chown=<user>:<group>] <src> .. <dest>
Example
Shell Form
Executable Form
copy src dest copy [“src”,”dest”]
copy /root/testData /data/
INSTRUCTION LIST
EXPOSE
EXPOSE sends information to Docker that the container listens on the specified
network ports at runtime.
Syntax: EXPOSE <port>[PORT/<PROTOCOL>
Remember:
Docker uses this information to interconnect containers using links and to set up
port redirection on docker host system.
Example:
expose 80 443
INSTRUCTION LIST
ENV
ENV is a key-value pair. It sets the <KEY> , an environment variable, to the value
<VALUE>.
These variables will be set during the image build also available after the container
is launched.
Syntax: EXPOSE <port>[PORT/<PROTOCOL>
Remember:
Examples:
env app_dir /data/
INSTRUCTION LIST
USER
USER assigns user name and user group while running the image. It also assigns
user name and user group for the RUN, CMD, and ENTRYPOINT instructions.
Syntax: USER <USER>:<GROUP>
Example :user webadmin
Remember:
USER instruction is used to set the username,group name, UID and GID for
running subsequent commands. Else root user will be used.
INSTRUCTION LIST
VOLUME
VOLUME creates a mount point with a specific name.
Syntax: VOLUME ["/data"]
Example volume /data
Remember:
VOLUME instruction is used to create or mount a volume to the docker container
from the docker host filesystem.
INSTRUCTION LIST
WORKDIR
WORKDIR sets the directory for RUN, CMD, ENTRYPOINT, COPY, and ADD
Syntax: WORKDIR /path/to/workdir
Example: workdir /app/
Remember:
WORKDIR instruction is used to set the working directory.
INSTRUCTION LIST
ARG
ARG defines the variables that are passed by the user to the builder at the build-
time.
Syntax: ARG <name>=<default>
Example: arg tmp_name mycustom_image
Remember:
ARG instruction is also used to set environment variables with key and value, but
this variables will set only during the image build not on the container
IMP
V How to Optimize a Docker File
Remember:
1 Always use Alpine 5 Reduce Number of Layers created byDockerFile
2 Using Dockerignore 6 Build Custom Base Images
3 Use Multi Stage Build 6 Only Install Necessary Packages
4 Keep Application Data outside the Container!
Practice Assignment
1 Run Jenkins on a DO in a dockerized container and add volume to the container
Run SONARQUBE on a DO in a dockerized container and add volume to the
2 container
