DevOps Classroomnotes 08/Apr/2023

How Isolations are created or How Containers Work

• Each container is getting a
  • new process tree
  • disk mounts
  • network (nic)
  • cpu/memory
  • users
• Refer Here for Docker Internals
  

Docker Architecture

Generation 1:

• This was first gen, Where docker daemon used lxc (a linux kernel feature) to create containers
  

Generation2:

• Since docker was relying on lxc which was kernel feature, updates to kernel frequently used to break containers created by docker.
• So docker has created its own component called libcontainer (libc) to create containers.
• Docker wanted containers to be multi os and lxc was definetly not the way forward.
  
• Adoption of docker was drastically increased as it was stable.

Generation 3:

• In this generation, docker engine was revamped from monolith to multi component architecture and the images and containers were according to OCI (open container initiative) image spec and runtime spec.
• In the latest architecture
• docker daemon exposes api’s to listen requests from docker client.
• Passes the requests to containerd. This manages the lifecylcle of container
• containerd forks a runc process which creates container. once the container is created the parent of the container will be docker shim
  

Creating our first docker container

• docker container creation:
• To create container we need some image in this case lets take hello-world
• The command docker container run hello-world executed
• What happens
  • docker client will forward the request to docker daemon
  • docker daemon will check if the image exists locally. if yes creates the container by using image
  • if the image doesnot exist, then docker daemon tries to download the image from docker registry connected. The default docker registry is docker hub.
  • Downloading image into local repo from registy is called as pull.
  • Once the image is pulled the container is created.
    
• Registry is collection of docker images hosted for reuse.
• Docker hub Refer Here

Playing with containers

• Create a new linux vm and install docker in it
  
  
• Open all the ports
  • AWS
    
    
  • Azure
    
    

Check docker images in the host

pull the images from docker hub

• image naming convention

[username]/[repository]:[<tag>]
shaikkhajaibrahim/myspc:1.0.1
username => shaikkhajaibrahi
repository => what image => myspc
tag => version => 1.0.1

• default tag is latest

nginx
nginx:latest

• official images dont have username

nginx
ubuntu
alpine
shaikkhajaibrahim/myspc

• Lets pull the image nginx with tag 1.23

docker image pull nginx:1.23
docker image ls

* Lets pull the jenkins image with latest version

* Lets find the alpine and pull the image

Remove images from local

• Every image will have unique image id and image name
• We can delete individually docker image rm alpine:3.17
• if i have to delete all the images `docker image rm $(docker image ls -q)
  
  

Create a container with nginx

• To create and start the container we use run command
  
• note: i will be using -d for some time and we will discuss importance of this in next session
• every container gets an id and a name. name can be passed while creating container, if not docker will give random name
  
• Remove all the running containers docker container rm -f $(docker container ls -q )
  
  
• Remove specific container
  
• Remove all containers docker container rm -f $(docker container ls -a -q )
  
• Exercise: Start and stop containers