2-components.txt

Pod:
- smallest unit of k8s.
- abstraction over container - we can use multiple container technology.
- Usually meant to run 1 application inside a pod.
- Each pod get it's own IP address.
- Pods are ephemeral - means they can die.
- On death, they get new IP address.

Service:
- permanent IP address.
- Even if pod dies, service stays alive.
- External-service (protocol + node IP address + port) and internal-service.

Ingress:
- it does forwarding to service.

ConfigMap:
- external config of app, ex - urls of database.
- pod connects to it and get stuff from config-map.
- we can't keep password & username here.

Secret:
- used to store secret data.
- base64 encoded format.
- certificates, etc.
- is a load balancer as well.

Volumes:
- Persistent storage - on local node or external to cluster.
- k8s doesn't manage data persistence or replicating or backing up , etc.

Deployment:
- Blueprint for pods / replicas.
- we work with deployments and not pods.

Stateful-Set:
- Db cant be replicated via deployment.
- To avoid data inconsistencies, do replication, etc.
- mysql, mongodb, elasticsearch, etc.
- db read / writes are synchronized to avoid inconsistencies, etc.
- Complex to setup and recommended to use external db.