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kubernetes/components.md

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+## Worker Node
+can be a physical server, virtual machine, etc
+
+made up of........
+## pods
+- a wrapper over a container so that Kubernetes can replace them if necessary
+- there is usually 1 application per pod (or 1 application with a helper)
+
+
+**pods are EPHEMERAL** (they can die very easily)
+★ for example, if the app contained in the pod's wrapped container crashes, runs out of resources, etc
+
+when this happens, a new pod is created in it's place, with a new address.
+To work with this, we attach a.....
+
+## Service
+- a static IP address that is attatched to each pod/app
+- an app (stored in a node) will have it's own service/database, and every pod will have it's own service
+- the service lifetime is not connected to the pod's, so when the pod is replaced, the same internal IP can be used
+- also works as a load balancer when allocating requests to pods
+
+
+There are **two types of services**
+1. internal
+    - this is the default type
+    - can not be accessed externally
+2. external
+    - you must specify this when creating a service
+    - can communicate externally (i.e. via browser for a web app's endpoint)
+    - can be accessed via http://[node_ip_addr][service_port_number]
+
+what if you want to access something, but it needs to be via some sort of domain?
+use.....
+
+## Ingress
+- exposes HTTP and HTTPS routes from outside the cluster to services within the cluster
+- you set **rules**, which will then decide how requests are routed (forewarded to services or otherwise)
+
+<hr>
+
+## ConfigMap
+- external configurations for your application (i.e. database urls)
+- connected to pods so that they have access to this data
+- this allows you to just change the value in the configMap without re-building the pods
+- stored in plaintext
+
+**HOWEVER**
+This type of storage is ***NOT*** secure, so kubernetes offers.....
+
+## Secret
+- just like configMap, but for secrets (i.e. usernames, passowrd, etc)
+- stored in base64-encoded format
+- is meant to be encrypted using third-party tools (perhaps given by the cloud provider)
+
+
+**BOTH** ConfigMap and Secret can be used inside of pods like env vars or as a properties file
+
+<hr>
+
+## Volume
+- used for data storage
+★ imagine there is a "database" pod. If that pod restarts, your data is gone
+- attaches physical storage to a pod
+- can be on the same machine the pod is running on or a remote source outside of the cluster
+- **kubernetes does not manage data persistance**