Completek8s Classroomnotes 30/Jun/2023

Running Docker Containers

Interactions

• We can interact with running or stopped containers
  • attach: We will be able to connect to containers main process’s STDIN/STDOUT/STDERR.
  • cp: This allows to send or recieve content to/from container
  • exec: Execute a command inside containers’s isolation.
  • logs: Here we can review all the STDERR and STDOUT
• Playground
  • Run a jenkins contianer in a detached mode
    
  • now attach to the jenkins container
  • now if we execute ctrl+c i.e. exit the main process will be exited and the container will go into exited state
  • To view logs use docker container logs <cont-id/cont-name>
  • Copy files from docker host into contianer
    
  • Copy files from container into docker host
    

Limiting Host resources

• Lets review some options for container resource consumption. We will be able to limit access to CPU,memory and block devices
• There are two types of limits
  • soft limits: These represent reservation i.e container could consume more than declared but mininum soft limit
  • hard limits: Thse represent container will not get more than declared value
• Container by default can consume all of host resources (no limits)
• Options:
  • –cpu-period and –cpu-quota: This is specified in micro seconds and will modify cpu limits
  • –cpu-shares: This manages weight for containers main process. This is soft limit.
  • –cpus
  • –memory: maximum amount of memory for your container (hard limit)
  • –memory-reservation: this is soft limit
  • –blkio-weight
  • –blkio-weight-device

Building Docker Images

• Docker image is required to create container.
• Docker images are OCI compliant i.e. they can be executed in other container runtimes as well
• Docker image will have all the necessary contents to run an application
• We need to build docker images to run our application inside container. This process is called as Containerization
• To Build docker images we have 3 ways
  • Start from scratch and add components file by file
  • Create a container with some image, make changes to run your application and create a image from the running contianer (commit)
  • Using a file with all the instructions to create image (Dockerfile)

Creating images from scratch

• Docker has a reserved image (base-image) that is is empty & is known as scratch
• Even os components which are necessary to start the main process in container has to be copied by us

Creating Images interactively

Game of life

• Refer Here for the war file
• To run this application we need tomcat 8 or 9 with jdk 8 installed
• Copy the war file into webapps folder

sudo apt update
sudo apt install openjdk-8-jdk tomcat9 -y

• Create a container in an interactive way or detached mode

docker container run -d -p 37000:8080 --name gol tomcat:9-jdk8
docker container exec -it gol /bin/bash
cd webapps
wget https://referenceapplicationskhaja.s3.us-west-2.amazonaws.com/gameoflife.war
# now access the application over http://<ip-docker-host>:37000/gameoflife

* Now lets create a new container with this image and it works as shown in class

Exercise

• Create a docker image using commit command for
  • spring petclinic
  • nopcommerce