DevOps Classroomnotes 26/Aug/2023

Interacting with containers

• Use the exec of the docker container command
  
• We can execute interactive commands by using shell
  
• Recommended Practice:
  • Run the container in a detached mode and use exec/logs for experimentation.

Containerization using Dockerfile

• Dockerfile is a set of instructions which help in building the docker image.
• To build a docker image (which is oci compliant) we need to
  • choose a base image
  • provide additional instructions to containerize the application
• docker image build command does the image building process by creating a container, executing instructions and creating the docker image
• The base image is required to set necessary stuff, if you want to build a docker image from scratch we can use base image scratch
• The instructions in docker file INSTRUCTION <value>
• Refer Here for whole set of instructions

FROM: set base image

• Refer Here for official docs

LABEL: set metadata

• Refer Here for official docs

RUN: execute instructions for configuring your application

• Refer Here for official docs

CMD: run the command during startup

• Refer Here for official docs

Expose: expose container ports

• Refer Here for official docs

Image building ways of working

• Create a newfolder or choose an existing folder. Create a file called as Dockerfile.
• Generally Dockerfile is present with the source code.

Building springpetclinic

• Refer Here for the first set of changes (https://github.com/asquarezone/DockerZone/commit/1629a1f639be4e756b021107d1dfa1ef812a4145?diff=split)
• Now build the image with tag 1.0.0 and repo spc
• The command is docker image build -t spc:1.0 .
  
  
• Now add labels Refer Here for changeset and below for image building, lets use the same tag and repo
  
• When we repeatedly use same repo and tags there is a chance that some earlier builded images will get a repo name and tag name as <none>
• Refer Here for the changes done to download the spring petclinic into the docker image.
• Now lets build the image with same repo spc and tag 1.0.1
  
• the Failure wget not found represents the wget not present in the base image, So we have two options
  • find an alternative command
  • install wget
• We have used the alternative to use curl Refer Here for changes
• Now lets build the image with same repo spc and tag 1.0.1
  
• Refer Here for adding the expose information.
• Now build the image with same repo spc and tag 1.0.2
  
  
• Now lets create the container from spc:1.0.2 and we observed the container went into exited state
• Now add the CMD to start the application, build the image with repo spc and tag 1.0.3 Refer Here for the changes in Dockerfile
  
• Note: 1.0.3 failed due to wrong argument Refer Here for fix
• Now create the container using spc:1.0.4
  
  
• Generally slim or alpine base images will reduce image size Refer Here for the changes to use alpine jdk 11 as a base image
• Build the image with repo spc:1.0.0-slim
  
• run the contianer