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SQL Operation	Purpose	MongoDB	Cassandra	DynamoDB
SELECT	Fetch data	find() or aggregate()	SELECT	GetItem, Query, Scan
WHERE	Filter rows	find({ field: value })	WHERE clause	KeyConditionExpression, FilterExpression
JOIN	Combine tables	$lookup in aggregation	Not supported (manual in app)	Not supported (manual in app)
UNION	Combine results	$unionWith (MongoDB 4.4+)	Not supported	Merge results in app
GROUP BY	Group record

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Component	Description
🌐 CoreDNS	Provides DNS-based service discovery for Pods. Every service gets a DNS entry.
📊 Metrics Server	Collects metrics like CPU/memory usage used for auto-scaling.
🖥️ Kubernetes Dashboard	A web-based UI for managing and visualizing your cluster.
🔒 Secrets & ConfigMaps	Manage application configurations and sensitive information securely.

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Component	Description
👷 Kubelet	An agent that runs on each node and communicates with the API Server. It ensures containers in Pods are running and healthy.
🔗 Kube-Proxy	Manages network rules and handles traffic routing to the correct Pods (load balancing, service discovery).
📦 Container Runtime	The underlying container engine like Docker, containerd, or CRI-O that actually runs your containers.

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Component	Description
🧩 API Server (kube-apiserver)	Central access point to the cluster. All commands (CLI, dashboard, etc.) go through this.
🧠 Scheduler (kube-scheduler)	Assigns Pods to Nodes based on available resources and constraints.
🔁 Controller Manager (kube-controller-manager)	Runs background processes (controllers) to ensure the desired state of the cluster (e.g., replicas, nodes, jobs).
🧾 etcd	A distributed key-value store to store all cluster

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Component	Role
API Server	Entry point to the cluster; all communication (kubectl, tools, etc.) goes through here
Scheduler	Assigns Pods to the most suitable Nodes based on resources
Controller Manager	Watches cluster state and takes actions to maintain desired state (e.g., restart pods)
etcd	Key-value store that holds cluster data and configuration (like a database)

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Orchestration Task	What Kubernetes Does
Scheduling	Decides which machine (node) should run which container
Scaling	Automatically adds or removes containers based on load
Self-healing	Restarts failed containers, reschedules them if a node goes down
Service Discovery	Automatically assigns DNS and handles IPs
Load Balancing	Distributes traffic evenly across multiple instances
Rollouts & Rollbacks	Deploys updates gradually and rolls back if errors occur
Configuration & Secrets Management	Injects environment configs securely at runtime
**Monitoring & Logging Integrati

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Network Type	Description	Use Case
bridge	Default for standalone containers. Creates a private internal network.	Local development or single-host setup
host	Shares the host’s network stack. No isolation.	High-performance use (e.g., games, VPNs)
none	No networking. Totally isolated.	Debugging, full manual control
overlay	Used in Docker Swarm. Connects containers across multiple Docker hosts.	Distributed systems (Swarm mode)
macvlan	Assigns a MAC address to container. Acts like a physical device.	Legacy systems that need real IPs

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Imp. Component	Description
Dockerfile	Instructions to build images
Docker Image	Blueprint for containers
Docker Container	Running instance of an image
Docker Registry	Stores and shares Docker images
Other Component
Docker Client	CLI to talk to Docker daemon
Docker Daemon	Core engine that runs containers/images

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Feature	Virtual Machine	Docker Container
OS	Full OS (guest + host)	Shares host OS kernel
Size	Heavy (GBs)	Lightweight (MBs)
Boot time	Slow (minutes)	Fast (seconds)
Resource usage	High	Low
Isolation	Full isolation	Process-level isolation

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Aspect	Orchestration	Choreography
Coordinator	Yes — a central Orchestrator service	❌ No — coordination is decentralized
Flow Control	Centralized logic	Each service decides what to do next
Communication Style	Typically command-driven (REST, sync)	Event-driven (asynchronous, e.g., Kafka)
Scalability	Can become a bottleneck	More scalable
Coupling	More tightly coupled to orchestrator	Loosely coupled