# 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/](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*