🧱 1. Pods (Smallest unit in Kubernetes)

🟦 What is a Pod?

A Pod is the smallest deployable unit in Kubernetes.
It contains one or more containers that always run together.

🧠 Think of a Pod like:

A wrapper around your container(s).

Each Pod gets:

• Its own IP address
• Shared network namespace
• Shared storage volumes

Example:

A Pod might contain:

• 1 container → nginx or
• 2 containers → app + sidecar (logging agent)

Why Pods exist:

Containers need a Kubernetes-native “package” to run inside the cluster.
That package is a Pod.

📦 2. Deployments (Controllers that manage Pods)

🟦 What is a Deployment?

A Deployment is a Kubernetes object that tells the cluster:

“Run this many Pods, keep them healthy, and update them safely.”

A Deployment manages:

• Creating Pods
• Maintaining replica count
• Rolling updates
• Rollbacks
• Self-healing

Example:

replicas: 5

Deployment ensures 5 pods always exist.

✔ Why Deployments exist:

Pods are not self-healing and not scalable.
Deployments add automation around Pods.

🌐 3. Services (Stable access to Pods)

🟦 What is a Service?

A Service provides a stable IP and DNS name to access Pods.

Pods come and go → their IPs change
Service → always stays the same

What Services do:

• Load-balance traffic to Pods
• Provide stable access even if Pods restart
• Allow communication between microservices

Types of Services:

• ClusterIP (default, internal)
• NodePort (expose app on node’s port)
• LoadBalancer (cloud load balancer)
• Headless Service (no load balancing, direct DNS)

✔ Why Services exist:

Without Services, apps inside Kubernetes would not know how to talk to Pods.

🗂️ 4. Configurations (ConfigMaps & Secrets)

🟦 What are Configurations?

They are Kubernetes objects used to store settings for applications.

Two types:

ConfigMap

Stores non-sensitive data:

• App settings
• File contents
• Environment variables

Secret

Stores sensitive data:

• Passwords
• API keys
• Certificates

✔ Why Configurations exist:

You should never hard-code sensitive or dynamic values inside the container image.
Kubernetes stores them separately and injects them at runtime.

🧠 5. State of Every Component (What Kubernetes stores in etcd)

🟦 What is the “State” of a Component?

State means the actual condition of something right now.

Kubernetes stores the state of everything in etcd, such as:

Pods’ state:

• Running
• Pending
• Failed
• Restarts
• Conditions
• Node assigned

Deployment state:

• How many replicas are running
• How many updated replicas
• Rollout status

Node state:

• Healthy or NotReady
• Resource usage
• Labels and taints

Service state:

• ClusterIP
• Endpoints (which Pods it is routing to)

ConfigMap/Secret state:

• Key-value pairs
• Version

Container state:

• Ready
• Started
• Exit codes
• Crash loops

🟩 Why Kubernetes stores state:

• To know desired state (what you want)
• To know actual state (what is happening)
• To let controllers fix mismatches

Example:
Desired: 5 Pods
Actual: 3 Pods running
→ Controller creates 2 new Pods automatically

🎯 Final Summary