Docker

Architecture

• Refer Here and look into underlying components
  

Running & Executing in containers in different modes

• Containers by default run in attached mode which displys in the stdout, stderr in the current terminal

docker run --name web1 nginx

• Containers can be run in the background without blocking terminal which is referred as detached mode, which returns a container id

docker run -d --name web2 nginx

* Other mode is interactive terminal, when you want to run a shell (we will discuss further later)
* Once the container is running we can execute commands in the container
* docker exec
* docker exec -it <bash|terminal>

Containerizing applications using Dockerfile

• Dockerfile is a text file which contains instructions to create docker image
• Instructions will have the following form

<INSTRUCTION> <VALUE>

• Dockerfile has lots of instructions supported
  
• Lets define some popular instructions
  • FROM
  • RUN
  • ADD | COPY
  • CMD
  • EXPOSE
  • LABEL
• FROM: this instruction defines the base image
• LABEL: This is used to add metadata
• RUN: This runs a command during image building
• CMD: This command executes when creating a container
• ADD | COPY: They are used to copy files or directories into image
• EXPOSE: This publishes the port on which your application is accessed.

Lets containerize the website used in previous class

• Refer Here for previous classroom notes
• Create a new folder called website and create a new file in this folder with name Dockerfile
• Refer Here for the changes done
• To build the docker ensure your are in the folder where Dockerfile exists
  & Execute

docker image build -t villa:1.0 .

• The Dockerfile used is

FROM nginx
ADD html/ /usr/share/nginx/html
EXPOSE 80

Lets containerize the application

• Refer Here for the spring pet clinic
• The manual step to run this application is
  • Ensure jdk 17 is installed
  • java -jar spring-petclinic-3.3.0-SNAPSHOT.jar is the command to start the application
  • This application runs on port 8080
• Approximate Dockerfile

FROM openjdk:17
ADD https://referenceappslt.s3.ap-south-1.amazonaws.com/spring-petclinic-3.3.0-SNAPSHOT.jar /spring-petclinic-3.3.0-SNAPSHOT.jar
EXPOSE 8080
CMD java -jar /spring-petclinic-3.3.0-SNAPSHOT.jar