Docker and Kubernetes notes

[Raw notes from this free course: https://www.udacity.com/course/scalable-microservices-with-kubernetes–ud615 ]

Docker is one of the most famous container in use nowadays.

Docker container features/best practise:

  • is portable because you keep all what you need for your application in it (libraries etc) – always run the same, regardless of the environment;
  • reduce conflicts between teams running different software on the same infrastructure;
  • minimal: best practise is to keep as minimal as possible its content;
  • you can ‘freeze’ it and move to another host, if required (using the cgroup capability);
  • no hard coded values in it: variable passed during the deploy or pulled from a file mounted externally;
  • you can mount external storage;
  • you can expose a port -> for example you can have a web app listening on port 80. You can expose port 80 of your container so when you connect to the host’s port 80, traffic will be redirected to the container. This “port forwarding” is the container runtime’s job;
  • ‘Dockerfile’ is the configuration file for the container. You can speficy the image that you want to use (FROM …), which port to expose, the storage to mount etc;

COMMANDS:

docker images -> shows current images downloaded

docker pull <image_name:version>

docker run -d <image_name:version>

docker ps

docker inspect <id>

docker stop <id>

docker rm <id>

 
Dockerfile

FROM -> which base image => alpine (small/package manager)
ADD take file/dir and put into the container
ENTRYPOINT what to run when you start the container

 

Push container to repository
Dockerhub -> default public (you can also have private)

docker tag -h
Add tag – then login and push

 

Create/Package container (5% of the work)

  • App configuration
  • Service Discovery
  • Managing Updates
  • Monitoring

Kubernetes -> Cluster like single machine
You need to describe the apps and how they interact between each others

POD
– collection of containers (possible multiple apps on different containers)
– shares network namespace (IP)
– shares storage volumes

=> created with conf files

Monitoring
Rediness -> container ready
Liveness -> app not working / restart app
Configmaps
Secrets

Services -> labels

Deployments
Desidered state

Scaling -> increase “replicas”

Rolling updates – CTO roll => deploy new version, get traffic, stop traffic prev version, remove prev verision (this per each POD)