learn/kubernetes/configuration.md

Communicating with the Master Node

Format

a request must be in YAML format and has:

1. apiVersion

   • the api version

2. kind

   • the kind of thing this is referring to (Service, Deployement, etc)

3. metadata

   • name of component
   • matchLabels (labels)
     • this is like a tag for that component to be matched by selectors
     • this is ONLY used by selectors ONE LAYER UP (i.e. service --> deployement/pods)

4. spec (specification)

   • any configurations you might need (selector, port, etc)
   • this will be kind specific
   • this section will be expanded on down below

5. status

   • this is automatically generated by kubernetes
     ★ for example, if you put replicas: 2 under spec, kubernetes will add a status that lets it know that only 1 state is currently running, then continuously update it as new replicas are added or removed, change the number of replicas accordingly
   • kubernetes gets this data from the etcd and compares it to your request
     ★ YAML is horrid, so consider using a tool like https://yamlchecker.com/

The Spec Field

This gets it's own section because it can contain so many things. For example:

Pod Blueprints

• stored in the template field, these are the blueprints for the pods
• these will have their own spec and metadata fields in them
• like nested configuration files as pods need their own configuration "files" inside of the deployement's configuration file

Selectors

• tells the deployement what label to match
• this is ONLY used by selectors ONE LAYER DOWN (i.e. deployement/pods --> service)

Ports

• the service has a port where it is accessible at
  • this is the port variable
• the service also needs a protocol which it is accessible by
  • this is the protocol variable
• the service also needs to know what port the pod to be contacted is listening on
  • this is the targetPort variable
• the pod has a port it is listening on
  • this is the containerPort variable

Note: these files are declarative, so for example if you specify there must be 3 replicas, kubernetes will try to ensure there are three replicas