Docker and Kubernetes

Docker

• Why? Makes it easy to install and run software without dependencies worrying
• What? Platform or ecosystem around creating and running containers (Client, Server, Hub, Image)

Docker Image - Single file with all the deps and config to run a program Docker Container - Instance of image - runs a program

Tools:

• Docker CLI - issue commands
• Docker Server - create images, run containers

Docker Run Command:

1. grabs image from Docker Hub
   1. first time to image local cache
2. creates container out of the image

How to separate process (belong to linux):

• Namespacing - isolate resources per process
• Control groups - limits amount of resources used per process

Container - Set of processes with grouping of resources assigned to it

• Running process with subset of resources from PC

Image:

• Filesystem snapshot - lower level under kernel
• Startup command - higher level to run

Docker has:

• Linux VM with each own its kernel (so it can separate processes)

2 - Manipulating Containers with the Docker Client §

docker run <image name> command!

• docker - reference docker client
• run - create and run container
• command! - default command override
  • May not work if the image does not have an actual executable file

docker ps - shows running container

• --all - shows all containers ever ran

docker run = docker create + docker start

1. docker run hello-world
2. docker create -a 0316c4a3365342583ed368d98fd726a988d2811f066edf2b0920a40fbc6020e6
   • -a - give output coming from container
3. docker system prune - removes all containers and others (networks, deps)
4. docker logs <container id> - get logs after docker start
5. docker stop <container id> - Send SIGTERM to shutdown process at its own time for cleanup (about 10s grace time)
   • With ping command, never wants to stop so just auto after 10s
6. docker kill <container id> - Kills instantly

Running multi-command containers §

Problem - containerized server (redis-server) cannot listen to a port number anymore Solution - Put the listener (redis-cli) also inside container asdd execute additional command

docker exec -it container-id command

• exec - run another command
• -it - listens to input
• docker exec -it container-id redis-cli

it flag - combination of -i and -t flag

• -i flag - ensures stdin to the command
• -t flag - ensures text entered is formatted

docker exec -it container-id sh

• full container access to manipulate
• other terminals - bash, powershell, zsh, sh

docker run -it busybox sh - to poke around containers, cannot run other processes

• isolated, 2 processes are unique and not share files or others

3 - Building Customer Images through Docker Server §

Dockerfile -> Docker Client -> Docker Server -> Usable Image

Dockerfile - configuration to define how container behave

Creating dockerfile:

1. Specify base image
2. Run some commands to install deps
3. Specify command to run on start

docker build . on a dir with dockerfile

FROM alpine

# Step 2: Download and install dependency
RUN apk add --update redis

# Step 3: Tell the image what to do when it starts as container
CMD ["redis-server"]

Wrtiting dockerfile == Installing Chrome with computer with no OS

Use alpine as base image - includes programs enough to run

• apk add to install redis

Build process - almost every step (after step 2), make a new intermediate container with the new FS snapshop. shutdown the container and get image ready

• Caching happens and not do any fetching anymore but ensure that dependency is the same

Tagging image - -t brianrahadi/redis:latest

• docker build -t brianrahadi/redis:latest .

Manual image generation with docker commit

• docker commit -c 'CMD ["redis-server"]' e444cc643230