Components

Node and Pod

Node

• Physical or virtual machine in the Kubernetes cluster

• Hosts one or more pods

Pod

• Smallest deployable unit in Kubernetes

• Abstraction layer over a container (e.g., Docker)

  • Allows Kubernetes to remain agnostic to container runtime

• Pod Types:

  • Single-container pod: Most common usage

  • Multi-container pod: Used when helper or sidecar containers are required (e.g., logging agent)

Communication

• Pods communicate using internal IPs provided by Kubernetes virtual network

• IPs are assigned to pods, not containers

Ephemeral Nature

• Pods are short-lived and can terminate due to:

  • Application crash

  • Resource exhaustion on node

• When restarted:

  • A new pod is created

  • A new internal IP is assigned

Service

Purpose

• Abstracts and stabilizes pod communication

• Provides permanent virtual IPs and DNS names for accessing pods

Types of Services

• Internal Service:

  • Used for communication between internal components (e.g., app to database)

  • Example: Database service within the cluster

• External Service:

  • Exposes application to external traffic

  • Example: Making the app accessible via a browser

Use Case

• Prevents the need to track changing pod IPs

• Allows stable communication channels

Ingress

Purpose

• Manages external access to services via HTTP/HTTPS

• Enables:

  • Custom domain names

  • Secure protocol (HTTPS)

• Routes requests to the appropriate service

Example

• Without Ingress: http://<Node-IP>:<Port>

• With Ingress: https://myapp.mydomain.com

ConfigMap

Purpose

• Externalizes non-sensitive application configuration

• Avoids hardcoding values inside container images

Use Case

• Useful for storing:

  • Service URLs

  • Feature flags

  • Environment-specific values

Benefits

• Simplifies deployment updates

• No need to rebuild and redeploy container images for configuration changes

Example

• Change database service name in ConfigMap instead of rebuilding the app image

Secret

Purpose

• Similar to ConfigMap, but for sensitive data

• Stores data in Base64 encoded format (not plain text)

Use Case

• Used for:

  • Passwords

  • TLS certificates

  • API keys

Integration

• Connected to pods via:

  • Environment variables

  • Mounted volumes as files

Best Practices

• Do not store secrets in ConfigMap

• Keep credentials separate and secured

Volumes

Purpose

• Provides persistent storage for data generated/used by pods

Problem Without Volumes

• Pod restart would lead to data loss since pods are ephemeral

Volume Types

• Local Volumes:

  • Stored on the same node as the pod

• Remote/External Volumes:

  • Cloud-based or on-premises

  • Not managed by Kubernetes, but mounted into pods

Use Case

• Persisting:

  • Database data

  • Application logs

Key Considerations

• Kubernetes does not handle:

  • Data backup

  • Replication

  • Storage hardware management

• User/admin is responsible for managing data persistence and integrity

Analogy

• Think of volumes as external hard drives plugged into the Kubernetes cluster