Kubernets Architecture

Master Node/Control Plane

User Interacts with Master node(using yaml file). Master node create/destroy worker nodes.
Daemon in master node

Name	Description
1. API Server	Manages all communication with Worker nodes(using kubelet)
1. etcd store	Stores state of kubernets cluster
3. Scheduler	Schedules pods to run on worker nodes
4. Controller Manager	Runs controllers that monitors state of cluster and maintains desired state
5. Add-ons	Provides additional functionality

Worker Node

Handles workload. Worker nodes hosts PODS. 1 Pod can contain 1 or more containers, Eg: docker.
Deamons in Worker Node

Name	Description
1. Kubelets	Recieves instructions from master node to run/manage container.
2. Container Runtime	This actually runs the container. Several runtimes kubernets supports: Docker, containerd, CRI-O
3. Kube-proxy	For communication with other nodes in cluster
4. Add-Ons	Additional functionality.
5. Node status & Meta-data	Each worker node maintains meta-data about itself. Example: IP Address, hostname, Current status (Ready, Not Ready, Out of Disk space etc)

POD

POD is smallest deployable unit in kubernets. 1 Pod can contain 1 or more containers
Each POD has its own: IP & namespace. Containers in POD share resources and can communicate using 'localhost' and can share storage volumes. Memory is allocated to Pods using Volumes.

Can Container has multiple executables running?
Yes, But its not recommended. Container should ideally run only 1 process.

Terms

Term

Description

Namespace

Divides cluster into smaller units to isolate services, volumes and manage. Namespace contains pods.
3 predefined namespaces: Default, Kube-system(resources created by kubernets), Kube-public(reserved for future)

Service (kubernets Networking objects)

Service is Networking abstraction which provides stable network access to pods.
service does not run inside containers, these are k8s objects. Each service routes the traffic to 1 or more POD
Service provides: Load balancing, service discovery, stable endpoints

PVC(Persistant Volume Claims)

Types of PVC

Type	Description
Config PVC	Store configuration files for the container(json, yaml, config) mounted at /etc/process-name inside container Multiple pods can read
Data PVC	Store application data,logs,database Mounted at /var/lib/process-name inside container Only 1 pod can write
Shared-Data PVC	To transfer files between containers Mounted at /shared/data inside container All containers can read/write

These are mounted at . Types
1. Config PVC: