Monday, 24 August 2026

kubernetes commands.

============================================================

KUBERNETES / KUBECTL COMMAND CHEAT SHEET

AWS EKS + SPRING BOOT

============================================================

# ==========================================================

# 1. KUBECTL / CLUSTER

# ==========================================================

kubectl version --client

kubectl cluster-info

kubectl config current-context

kubectl config get-contexts

kubectl config use-context <context-name>

# ==========================================================

# 2. NODES

# ==========================================================

kubectl get nodes

kubectl get nodes -o wide

kubectl describe node <node-name>

# ==========================================================

# 3. NAMESPACES

# ==========================================================

kubectl get namespaces

kubectl get ns

kubectl get all -n <namespace>

kubectl get all -n staging

# ==========================================================

# 4. PODS

# ==========================================================

kubectl get pods -n staging

kubectl get pods -o wide -n staging

kubectl get pods -w -n staging

kubectl describe pod <pod-name> -n staging

# ==========================================================

# 5. APPLICATION LOGS

# ==========================================================

kubectl logs <pod-name> -n staging

kubectl logs -f <pod-name> -n staging

kubectl logs --tail=100 <pod-name> -n staging

kubectl logs --since=30m <pod-name> -n staging

kubectl logs <pod-name> -c <container-name> -n staging

# ==========================================================

# 6. DEPLOYMENTS

# ==========================================================

kubectl get deployments -n staging

kubectl get deploy -n staging

kubectl describe deployment <deployment-name> -n staging

kubectl rollout status deployment/<deployment-name> -n staging

kubectl rollout history deployment/<deployment-name> -n staging

# ==========================================================

# 7. SERVICES

# ==========================================================

kubectl get services -n staging

kubectl get svc -n staging

kubectl describe service <service-name> -n staging

# ==========================================================

# 8. CONFIGMAPS

# ==========================================================

kubectl get configmaps -n staging

kubectl describe configmap <configmap-name> -n staging

# ==========================================================

# 9. SECRETS

# ==========================================================

kubectl get secrets -n staging

kubectl describe secret <secret-name> -n staging

# WARNING: May expose sensitive credentials

kubectl get secret <secret-name> -o yaml -n staging

# ==========================================================

# 10. EVENTS / TROUBLESHOOTING

# ==========================================================

kubectl get events -n staging

kubectl get events -n staging --sort-by=.lastTimestamp

# ==========================================================

# 11. EXECUTE COMMAND INSIDE POD

# ==========================================================

kubectl exec -it <pod-name> -n staging -- /bin/sh

kubectl exec -it <pod-name> -n staging -- /bin/bash

# Exit container

exit

# ==========================================================

# 12. RESTART DEPLOYMENT

# ==========================================================

kubectl rollout restart deployment/<deployment-name> -n staging

kubectl rollout status deployment/<deployment-name> -n staging

# ==========================================================

# 13. DELETE POD

# ==========================================================

kubectl delete pod <pod-name> -n staging

# ==========================================================

# 14. GET ALL RESOURCES

# ==========================================================

kubectl get all -n staging

# ==========================================================

# 15. SCALING

# ==========================================================

kubectl get deployment <deployment-name> -n staging

kubectl scale deployment <deployment-name> --replicas=3 -n staging

kubectl get pods -n staging

# ==========================================================

# 16. ROLLBACK

# ==========================================================

kubectl rollout history deployment/<deployment-name> -n staging

kubectl rollout undo deployment/<deployment-name> -n staging

kubectl rollout status deployment/<deployment-name> -n staging

# ==========================================================

# 17. FILTER BY LABEL

# ==========================================================

kubectl get pods -l app=<app-name> -n staging

kubectl get pods -l app=impress -n staging

kubectl get all -l app=impress -n staging

# ==========================================================

# 18. RESOURCE USAGE

# ==========================================================

kubectl top pods -n staging

kubectl top nodes

# ==========================================================

# 19. MOST IMPORTANT DAILY COMMANDS

# ==========================================================

kubectl config current-context

kubectl get ns

kubectl get pods -n staging

kubectl get pods -o wide -n staging

kubectl describe pod <pod-name> -n staging

kubectl logs <pod-name> -n staging

kubectl logs -f <pod-name> -n staging

kubectl get deploy -n staging

kubectl get svc -n staging

kubectl get events -n staging --sort-by=.lastTimestamp

# ==========================================================

# 20. SPRING BOOT / EKS TROUBLESHOOTING FLOW

# ==========================================================

kubectl config current-context

kubectl get ns

kubectl get pods -n <namespace>

kubectl get pods -o wide -n <namespace>

kubectl describe pod <pod-name> -n <namespace>

kubectl logs <pod-name> -n <namespace>

kubectl logs -f <pod-name> -n <namespace>

kubectl get events -n <namespace> --sort-by=.lastTimestamp

# ==========================================================

# 21. AWS EKS CONNECTION

# ==========================================================

# Check AWS identity

aws sts get-caller-identity

# If using a specific AWS profile

aws sts get-caller-identity --profile <profile-name>

# List EKS clusters

aws eks list-clusters --region <aws-region>

# Configure kubectl for an EKS cluster

aws eks update-kubeconfig \

--region <aws-region> \

--name <cluster-name>

# Example

aws eks update-kubeconfig \

--region us-east-1 \

--name staging-eksCluster-a11b87c

# Verify connection

kubectl cluster-info

# Check nodes

kubectl get nodes

# ==========================================================

# 22. QUICK EKS WORKFLOW

# ==========================================================

aws sts get-caller-identity

aws eks list-clusters --region <aws-region>

aws eks update-kubeconfig \

--region <aws-region> \

--name <cluster-name>

kubectl config current-context

kubectl get nodes

kubectl get ns

kubectl get pods -n staging

kubectl get deploy -n staging

kubectl get svc -n staging

kubectl logs -f <pod-name> -n staging

# ==========================================================

# IMPORTANT CONCEPTS

# ==========================================================

kubectl = Local Kubernetes command-line client

Cluster = Complete Kubernetes environment

Node = Machine/worker machine where Pods run

Pod = Kubernetes workload unit containing container(s)

Container = Actual application runtime, e.g. Spring Boot

Namespace = Logical separation inside a Kubernetes cluster

Deployment = Manages Pods, replicas and rolling updates

Service = Stable network endpoint for accessing Pods

ConfigMap = Non-sensitive application configuration

Secret = Sensitive configuration/credentials

RBAC = Kubernetes Role-Based Access Control

IAM = AWS identity and permission system

# ==========================================================

# KUBERNETES STRUCTURE

# ==========================================================

AWS EKS Cluster

+-- Node 1

| |

| +-- Pod

| | |

| | +-- Container

| | |

| | +-- Spring Boot Application

| |

| +-- Pod

+-- Node 2

| |

| +-- Pod

+-- Namespaces

+-- staging

+-- production

+-- monitoring

# ==========================================================

# APPLICATION DEBUGGING FLOW

# ==========================================================

Cluster

Namespace

Deployment

Pod

Container

Application Logs

# ==========================================================

# COMMON POD ERRORS

# ==========================================================

ImagePullBackOff

CrashLoopBackOff

Pending

FailedScheduling

FailedMount

ContainerCreating

Error

# ==========================================================

# SAFETY

# ==========================================================

# Always check which cluster you are connected to

kubectl config current-context

# Always check namespace before making changes

kubectl get ns

# Be careful with production:

kubectl delete ...

kubectl scale ...

kubectl rollout restart ...

kubectl rollout undo ...

# Be careful with secrets:

kubectl get secret <secret-name> -o yaml -n staging

Tuesday, 18 August 2026

Data dog data flow

Sunday, 3 May 2026

squash and merge

🔹 Step-by-step (squash your 5 commits into 1)

1. Go to your branch


git checkout your-feature-branch

2. Start interactive rebase (last 5 commits)


git rebase -i HEAD~5

3. You’ll see something like:


pick a1b2c3 add login UI
pick b2c3d4 fix bug
pick c3d4e5 update API
pick d4e5f6 fix typo
pick e5f6g7 refactor code

4. Change it to:

👉 Keep first as pick, rest as squash (or s)


pick a1b2c3 add login UI
squash b2c3d4 fix bug
squash c3d4e5 update API
squash d4e5f6 fix typo
squash e5f6g7 refactor code

5. Save & close editor

Git will now ask for a final commit message

Replace with something clean:


Add login UI with API integration, bug fixes, and refactoring

6. Done 🎉

Now all 5 commits = 1 commit

🔹 Important (don’t skip this)

If your branch is already pushed to remote:


git push --force

⚠️ This rewrites history—only do this on your feature branch, not shared branches like main.

🔹 Shortcut (if you don’t care about messages)

You can also do:


git reset --soft HEAD~5
git commit -m "Add login feature with all fixes"

🔹 Pro tip (real-world)

Use rebase squash → before PR
Use Squash & Merge → during PR
Avoid messy commits in main

If you want next level:
I can show how companies enforce this using Git hooks / CI rules (very useful for team lead role).

what it mens

Got it—you’re asking what this actually means 👇


git reset --soft HEAD~5
git commit -m "Add login feature with all fixes"

🔹 Simple Meaning

👉 This is a shortcut way to squash commits into one

Instead of using rebase -i, this does:

Go back 5 commits
Keep all changes in staging
Create 1 new commit

🔹 Step-by-step explanation

✅ `git reset --soft HEAD~5`

👉 Break it down:

HEAD~5 = go back 5 commits
reset = move branch pointer backward
--soft = DO NOT delete changes, keep them staged

So after this command:

✔ All 5 commits are removed
✔ But their code changes are still there
✔ And already staged (ready to commit)

✅ `git commit -m "..."`

Now you create one new clean commit:


Add login feature with all fixes

🔹 Visual understanding

Before:


commit1 -> commit2 -> commit3 -> commit4 -> commit5 (HEAD)

After reset:


(no commits)
but all changes are staged

After new commit:


single commit (combined work)

🔹 Key difference vs rebase

Method	Control	Use case
`rebase -i`	Full control	Best for clean history
`reset --soft`	Quick & simple	Fast squash

🔹 Important warning ⚠️

If already pushed:


git push --force

Otherwise remote will still have old commits.

🔹 One-line understanding

👉 git reset --soft HEAD~5 = remove last 5 commits but keep their changes staged

If you want, I can explain:

difference between --soft, --mixed, --hard (very important for interviews)

Tuesday, 28 April 2026

AWS S3 bucket tier.

S3 Storage Classes

│

├── Standard (manual, hot data)

│

├── Intelligent-Tiering (auto-managed)

│ ├── Frequent Tier ✅

│ ├── Infrequent Tier ✅

│ ├── Archive Tier ❌

│ └── Deep Archive Tier ❌

│

├── Standard-IA (manual, low cost, retrieval fee)

│

├── Glacier Flexible Retrieval ❌ (restore required)

│

└── Glacier Deep Archive ❌ (slow restore)

Wednesday, 15 April 2026

Open API documentation

https://learn.openapis.org/introduction.html

Wednesday, 18 March 2026

Design pattern

Let’s simplify everything from Refactoring Guru Design Patterns into very easy (lemon 😄) terms + real-world + Java/Spring examples.

🧠 First: What is a Design Pattern?

👉 A design pattern = proven solution to common coding problem

Think like:

“This problem already happened before → smart people solved it → reuse that solution”

🧩 3 Types of Design Patterns

1. 🏗️ Creational (Object banana ka tareeka)

How objects are created

2. 🧱 Structural (Object ko kaise jode)

How objects are structured/connected

3. 🔄 Behavioral (Object kaise behave kare)

How objects communicate

🏗️ 1. CREATIONAL PATTERNS (Creation)

1. Singleton 🧍

👉 Only one object in whole system

🍋 Lemon Example:

There is only one Aadhaar database

💻 Java Example:

class Config {
    private static Config instance = new Config();
    private Config() {}
    public static Config getInstance() {
        return instance;
    }
}

🔥 Real Use:

DB connection pool
Redis client
Spring Beans (default singleton)

2. Factory 🏭

👉 Object create karne ka decision system lega

🍋 Example:

You order coffee

Latte / Cappuccino / Espresso
System decides what to create

💻 Java Example:

interface Notification {}
class Email implements Notification {}
class SMS implements Notification {}

class Factory {
    public static Notification get(String type) {
        if (type.equals("email")) return new Email();
        return new SMS();
    }
}

🔥 Real Use:

Payment methods
Notification service

3. Builder 🧱

👉 Complex object step-by-step banana

🍋 Example:

Ordering pizza

size
cheese
toppings

💻 Example:

User user = User.builder()
    .name("Pawan")
    .age(30)
    .build();

🔥 Real Use:

DTO creation
Immutable objects

🧱 2. STRUCTURAL PATTERNS

4. Adapter 🔌

👉 Incompatible cheez ko compatible banana

🍋 Example:

Indian charger → US socket adapter

💻 Example:

Old API → New API wrapper

🔥 Real Use:

Third-party API integration (very important for you!)

5. Decorator 🎁

👉 Existing object ko extra feature dena

🍋 Example:

Coffee + milk + chocolate

💻 Example:

class Coffee {}
class MilkDecorator extends Coffee {}

🔥 Real Use:

Logging
Security layers

6. Facade 🏢

👉 Complex system ko simple interface dena

🍋 Example:

Swiggy app → kitchen, delivery, payment sab hide

💻 Example:

class OrderService {
    void placeOrder() {
        payment();
        inventory();
        delivery();
    }
}

🔥 Real Use:

Microservice orchestration

🔄 3. BEHAVIORAL PATTERNS

7. Strategy 🎯

👉 Multiple ways to do same task

🍋 Example:

Travel options:

Car
Bike
Train

💻 Example:

interface PaymentStrategy {
    void pay();
}
class UPI implements PaymentStrategy {}
class Card implements PaymentStrategy {}

🔥 Real Use:

👉 Your AWS SES email system can use this!

8. Observer 👀

👉 One change → multiple systems notified

🍋 Example:

YouTube subscribe → notification

💻 Example:

observer.update();

🔥 Real Use:

SNS, Kafka, Event-driven systems

9. Command 📦

👉 Request ko object bana do

🍋 Example:

Remote control button

💻 Example:

interface Command {
    void execute();
}

🔥 Real Use:

Queue (SQS)
Task execution

🚀 Most Important for YOU (Based on your work)

Since you're working with:

Spring Boot
AWS SES, SQS
Microservices

👉 Focus on:

Strategy → email sending logic
Factory → notification type
Observer → event system (SNS/SQS)
Facade → service layer
Builder → DTO creation

🎯 Simple Memory Trick

Type	Meaning
Creational	Object kaise banega
Structural	Object kaise judega
Behavioral	Object kaise behave karega

💡 Real-world Example (Your Project)

Your Email System:

Factory → choose Email/SMS
Strategy → SES / SMTP
Observer → Bounce/Delivery events
Command → SQS message

Facade → EmailService

Perfect — let’s go deep into Creational Patterns (this is where strong backend engineers stand out in interviews + system design).

I’ll explain:

Core idea (simple 🍋)
When to use (important!)
Internal thinking (how it works)
6+ real-world examples (with Java/Spring mapping)

🏗️ CREATIONAL DESIGN PATTERNS (Deep Dive)

👉 These patterns solve:

“Object kaise banega — simple, controlled, flexible way mein?”

1. 🧍 Singleton Pattern (One instance only)

🍋 Simple Idea:

System mein sirf ek hi object allowed

🧠 Why needed?

Avoid multiple expensive objects
Maintain shared state

⚙️ Internal Concept:

Private constructor
Static instance
Global access method

💻 Production-Ready Java (Thread-safe)

public class ConfigManager {

    private static volatile ConfigManager instance;

    private ConfigManager() {}

    public static ConfigManager getInstance() {
        if (instance == null) {
            synchronized (ConfigManager.class) {
                if (instance == null) {
                    instance = new ConfigManager();
                }
            }
        }
        return instance;
    }
}

🔥 Real-world examples (6+)

1. DB Connection Pool

DataSource ds = DataSourceSingleton.getInstance();

2. Redis Client

Jedis jedis = RedisManager.getInstance().getClient();

3. Logger (Log4j / SLF4J)

👉 Only one logger config

4. Spring Beans (Default)

@Service
class UserService {}

👉 Spring internally uses Singleton

5. Cache Manager

CacheManager.getInstance().put(key, value);

6. Configuration Loader

ConfigManager.getInstance().get("db.url");

⚠️ When NOT to use:

When object needs different states (use prototype)

2. 🏭 Factory Pattern (Object creation decision hidden)

🍋 Simple Idea:

“Tum bas bolo kya chahiye — system bana ke dega”

🧠 Why needed?

Remove new keyword everywhere
Loose coupling

💻 Example (Advanced)

interface Payment {
    void pay();
}

class UPI implements Payment {
    public void pay() { System.out.println("UPI"); }
}

class Card implements Payment {
    public void pay() { System.out.println("Card"); }
}

class PaymentFactory {
    public static Payment getPayment(String type) {
        switch(type) {
            case "UPI": return new UPI();
            case "CARD": return new Card();
            default: throw new IllegalArgumentException();
        }
    }
}

🔥 Real-world examples

1. Payment System

Payment p = PaymentFactory.getPayment("UPI");

2. Notification System

Notification n = NotificationFactory.get("EMAIL");

3. Spring BeanFactory

👉 Spring internally uses Factory

4. AWS SDK Clients

AmazonSQS sqs = AmazonSQSClientBuilder.defaultClient();

5. JDBC DriverManager

Connection con = DriverManager.getConnection(url);

6. Parser System

Parser parser = ParserFactory.get("JSON");

⚠️ Problem solved:

👉 No if-else everywhere

3. 🧱 Builder Pattern (Complex object creation)

🍋 Simple Idea:

“Step-by-step object banana”

🧠 Why needed?

Too many constructor arguments
Optional fields

💻 Example

class User {
    private String name;
    private int age;
    private String email;

    public static class Builder {
        private String name;
        private int age;
        private String email;

        public Builder setName(String name) {
            this.name = name;
            return this;
        }

        public Builder setAge(int age) {
            this.age = age;
            return this;
        }

        public Builder setEmail(String email) {
            this.email = email;
            return this;
        }

        public User build() {
            User u = new User();
            u.name = this.name;
            u.age = this.age;
            u.email = this.email;
            return u;
        }
    }
}

🔥 Real-world examples

1. HTTP Request (Spring)

ResponseEntity.ok().header("x","y").body(data);

2. Lombok Builder

User user = User.builder()
    .name("Pawan")
    .email("p@test.com")
    .build();

3. AWS SES Email

SendEmailRequest request = new SendEmailRequest()
    .withDestination(...)
    .withMessage(...);

4. Kafka Message Builder

ProducerRecord record = new ProducerRecord(topic, key, value);

5. Query Builder (JPA)

criteriaBuilder.createQuery(User.class);

6. Docker Config (Your project!)

👉 step-by-step container config

4. 🧬 Prototype Pattern (Clone object)

🍋 Simple Idea:

“Naya object banane ke bajaye copy karo”

🧠 Why needed?

Object creation expensive hai

💻 Example

class User implements Cloneable {
    String name;

    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

🔥 Real-world examples

1. Template Email Copy

Email copy = original.clone();

2. Spring Prototype Scope

@Scope("prototype")
@Bean
public User user() { return new User(); }

3. Object Copy in Cache

return cachedObject.clone();

4. Game Development (Characters)

5. Document Templates

6. Request Retry Copy

👉 same request clone

5. 🏢 Abstract Factory (Factory of factories)

🍋 Simple Idea:

“Factory bhi dynamically choose hogi”

🧠 Why needed?

Multiple related object families

💻 Example

interface UIFactory {
    Button createButton();
}

class WindowsFactory implements UIFactory {
    public Button createButton() { return new WindowsButton(); }
}

class MacFactory implements UIFactory {
    public Button createButton() { return new MacButton(); }
}

🔥 Real-world examples

1. Multi-cloud system (AWS/Azure)

CloudFactory factory = getFactory("AWS");
factory.createS3();

2. DB Support (MySQL / Mongo)

DAOFactory factory = getFactory("MYSQL");

3. UI Themes

4. Payment Gateway Providers

GatewayFactory.get("RAZORPAY");

5. Messaging Systems

Factory → Kafka / RabbitMQ

6. Your Microservice Design

👉 Per-tenant implementation

🧠 Interview-Level Insight

Difference:

Pattern	Key Idea
Singleton	One instance
Factory	Object creation logic
Builder	Step-by-step creation
Prototype	Copy object
Abstract Factory	Group of factories

🚀 YOUR PROJECT MAPPING (VERY IMPORTANT)

For your AWS Email System:

Component	Pattern
SES / SMTP switch	Strategy + Factory
Email Request	Builder
Event handling	Observer
Config	Singleton
Multi-provider	Abstract Factory

Perfect, Pawan — let’s design a real production-level Spring Boot microservice using ALL creational patterns together.

I’ll build this around something relevant to your work:
👉 Email Notification Service (AWS SES / SMTP / Future providers)

🚀 🏗️ SYSTEM OVERVIEW

🎯 Goal:

Send emails using different providers dynamically:

AWS SES
SMTP
Future: SendGrid

🧩 WHERE EACH PATTERN FITS

Pattern	Usage
Singleton	Config / AWS clients
Factory	Choose provider
Abstract Factory	Cloud provider family
Builder	Email request creation
Prototype	Retry email copy

📦 HIGH-LEVEL FLOW

Controller → Service → Factory → Provider → Send Email
                         ↓
                    Builder (email)
                         ↓
                  Prototype (retry)

1️⃣ 🧍 Singleton → Config Manager

👉 One config across system

@Component
public class AppConfig {

    private final Map<String, String> config = new HashMap<>();

    public AppConfig() {
        config.put("provider", "SES");
    }

    public String get(String key) {
        return config.get(key);
    }
}

✅ Spring makes it singleton automatically

2️⃣ 🧱 Builder → Email Object

👉 Complex object (to, subject, body, attachments)

public class Email {

    private String to;
    private String subject;
    private String body;

    private Email() {}

    public static class Builder {
        private String to;
        private String subject;
        private String body;

        public Builder to(String to) {
            this.to = to;
            return this;
        }

        public Builder subject(String subject) {
            this.subject = subject;
            return this;
        }

        public Builder body(String body) {
            this.body = body;
            return this;
        }

        public Email build() {
            Email email = new Email();
            email.to = this.to;
            email.subject = this.subject;
            email.body = this.body;
            return email;
        }
    }
}

3️⃣ 🏭 Factory → Provider Selection

public interface EmailProvider {
    void send(Email email);
}

Implementations:

@Component
public class SESProvider implements EmailProvider {
    public void send(Email email) {
        System.out.println("Sending via SES");
    }
}

@Component
public class SMTPProvider implements EmailProvider {
    public void send(Email email) {
        System.out.println("Sending via SMTP");
    }
}

Factory

@Component
public class EmailProviderFactory {

    @Autowired
    private SESProvider ses;

    @Autowired
    private SMTPProvider smtp;

    public EmailProvider getProvider(String type) {
        if ("SES".equalsIgnoreCase(type)) return ses;
        return smtp;
    }
}

4️⃣ 🏢 Abstract Factory → Cloud Providers

👉 Suppose future:

AWS (SES, SQS)
Azure (Email, Queue)

public interface CloudFactory {
    EmailProvider createEmailProvider();
}

AWS Factory

@Component
public class AWSFactory implements CloudFactory {

    @Autowired
    private SESProvider ses;

    public EmailProvider createEmailProvider() {
        return ses;
    }
}

Azure Factory (future)

@Component
public class AzureFactory implements CloudFactory {

    public EmailProvider createEmailProvider() {
        return new SMTPProvider();
    }
}

5️⃣ 🧬 Prototype → Retry Email

👉 Same email clone for retry

public class Email implements Cloneable {

    public Email clone() {
        try {
            return (Email) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new RuntimeException(e);
        }
    }
}

Retry Logic

public void retry(Email email) {
    Email copy = email.clone();
    send(copy);
}

6️⃣ 🎯 SERVICE LAYER (Putting everything together)

@Service
public class EmailService {

    @Autowired
    private AppConfig config;

    @Autowired
    private EmailProviderFactory factory;

    public void sendEmail(String to, String subject, String body) {

        // Builder
        Email email = new Email.Builder()
                .to(to)
                .subject(subject)
                .body(body)
                .build();

        // Factory
        String providerType = config.get("provider");
        EmailProvider provider = factory.getProvider(providerType);

        provider.send(email);
    }
}

7️⃣ 🌐 CONTROLLER

@RestController
@RequestMapping("/email")
public class EmailController {

    @Autowired
    private EmailService service;

    @PostMapping
    public String send() {
        service.sendEmail("test@mail.com", "Hello", "Body");
        return "Sent";
    }
}

🔥 REAL PRODUCTION ENHANCEMENTS (VERY IMPORTANT)

Since you're working on large-scale email system, add:

✅ 1. Strategy (Bonus pattern)

Switch providers dynamically:

Map<String, EmailProvider> providers;

✅ 2. Add SQS (Command pattern)

queue.send(emailRequest);

✅ 3. Observer (SES events)

Bounce
Delivery
Complaint

✅ 4. Rate Limiting

Avoid SES blocking (you faced this already)

✅ 5. Retry with Backoff

retry after 1s → 5s → 10s

🧠 HOW INTERVIEWER WILL TEST YOU

They will ask:

👉 “Design email system supporting multiple providers”

Your answer:

Builder → Email object
Factory → provider selection
Strategy → sending logic
Singleton → config
Prototype → retry

🔥 This is staff-level answer

🚀 NEXT LEVEL (I recommend)

If you want to go even deeper:

👉 I can upgrade this to:

Kafka-based event system
Fully async microservices
Circuit breaker (Resilience4j)
Multi-tenant email system (VERY IMPORTANT FOR YOU)

Just tell me:
👉 “Make it production-level architecture”

Tuesday, 17 February 2026

Spring boot annotation list

✅ 1. Core Spring / IOC & Bean Management

Stereotype annotations

@Component

@Service

@Repository

@Controller

@RestController

Configuration & Beans

@Configuration

@Bean

@Import

@ImportResource

@ComponentScan

@PropertySource

@Profile

@Scope

@Lazy

@DependsOn

@Primary

@Qualifier

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 1/2417/02/2026, 16:47 Spring Boot Annotations List

Dependency Injection

@Autowired

@Value

@Required

✅ 2. Spring Boot Specific

@SpringBootApplication

@EnableAutoConfiguration

@ConfigurationProperties

@EnableConfigurationProperties

@SpringBootTest

@TestConfiguration

@MockBean

@SpyBean

✅ 3. Web / MVC / REST

Controller & Mapping

@RequestMapping

@GetMapping

@PostMapping

@PutMapping

@DeleteMapping

@PatchMapping

Request handling

@RequestParam

@PathVariable

@RequestBody

@ResponseBody

@ResponseStatus

@RequestHeader

@CookieValue

@ModelAttribute

@MatrixVariable

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 2/2417/02/2026, 16:47 Exception Handling

@ExceptionHandler

@ControllerAdvice

@RestControllerAdvice

Spring Boot Annotations List

@CrossOrigin

✅ 4. Validation (JSR-303 / Hibernate Validator)

@Valid

@Validated

@NotNull

@NotEmpty

@NotBlank

@Size

@Min

@Max

@Positive

@Negative

@Email

@Pattern

@Future

@Past

@Digits

@AssertTrue

@AssertFalse

✅ 5. Spring Data JPA / Persistence

Repository

@Repository

@EnableJpaRepositories

Entity mapping (JPA)

@Entity

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 3/2417/02/2026, 16:47 Spring Boot Annotations List

@Table

@Id

@GeneratedValue

@Column

@Transient

@Lob

@Enumerated

@Temporal

Relations

@OneToOne

@OneToMany

@ManyToOne

@ManyToMany

@JoinColumn

@JoinTable

@MapsId

@Embedded

@Embeddable

Query

@Query

@NamedQuery

@Modifying

@Param

@Procedure

Transactions

@Transactional

✅ 6. Security (Spring Security)

@EnableWebSecurity

@EnableMethodSecurity

@Secured

@RolesAllowed

@PreAuthorize

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 4/2417/02/2026, 16:47 Spring Boot Annotations List

@PostAuthorize

@PreFilter

@PostFilter

@AuthenticationPrincipal

✅ 7. Scheduling & Async

@EnableScheduling

@Scheduled

@EnableAsync

@Async

✅ 8. Caching

@EnableCaching

@Cacheable

@CachePut

@CacheEvict

@Caching

✅ 9. Spring Cloud / Microservices (very common)

@EnableDiscoveryClient

@FeignClient

@EnableFeignClients

@LoadBalanced

@CircuitBreaker

@Retryable

@Recover

@RefreshScope

✅ 10. Messaging (Kafka / JMS / RabbitMQ)

@EnableKafka

@KafkaListener

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 5/2417/02/2026, 16:47 Spring Boot Annotations List

@SendTo

@EnableJms

@JmsListener

@RabbitListener

@RabbitHandler

✅ 11. Testing

@RunWith

@ExtendWith

@WebMvcTest

@DataJpaTest

@JdbcTest

@JsonTest

@RestClientTest

@AutoConfigureMockMvc

@AutoConfigureTestDatabase

@TestPropertySource

@ActiveProfiles

@DirtiesContext

@BeforeEach

@AfterEach

@BeforeAll

@AfterAll

@Test

✅ 12. AOP (Aspect Oriented Programming)

@Aspect

@Before

@After

@AfterReturning

@AfterThrowing

@Around

@Pointcut

@EnableAspectJAutoProxy

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 6/2417/02/2026, 16:47 Spring Boot Annotations List

✅ 13. Internationalization / Formatting

@DateTimeFormat

@NumberFormat

✅ 14. Conditional Annotations (Auto-Config magic)

@Conditional

@ConditionalOnBean

@ConditionalOnMissingBean

@ConditionalOnProperty

@ConditionalOnClass

@ConditionalOnMissingClass

@ConditionalOnWebApplication

@ConditionalOnNotWebApplication

@ConditionalOnExpression

✅ 15. Actuator

@Endpoint

@ReadOperation

@WriteOperation

@DeleteOperation

⚠

Reality Check

There is NO single official list called “all Spring Boot annotations” because:

Spring = Core + Web + Data + Security + Cloud + Test + Integration

JPA & Validation annotations come from Java EE / Jakarta

New annotations added every

version

If you really want absolute every annotation, you must scan packages:

org.springframework.*

jakarta.persistence.*

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 7/2417/02/2026, 16:47 jakarta.validation.*

org.springframework.boot.*

Spring Boot Annotations List

🎯 What I recommend for you (as a senior dev)

Master these 30 first:

less

Copy code

@SpringBootApplication

@Component

@Service

@Repository

@RestController

@Autowired

@Configuration

@Bean

@RequestMapping

@GetMapping

@PostMapping

@RequestBody

@PathVariable

@Transactional

@Entity

@Id

@OneToMany

@ManyToOne

@JoinColumn

@Query

@ExceptionHandler

@ControllerAdvice

@Scheduled

@Async

@Cacheable

@PreAuthorize

@FeignClient

@Test

@SpringBootTest

If you

want, next I can give you one of these (your choice):

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 8/2417/02/2026, 16:47 A) 📄 B) 🧠 C) 🔥 D)

Spring Boot Annotations List

PDF cheat sheet of all annotations category-wise

Diagram of Spring annotation layers

Interview-focused annotation list (top 50)

🧪

Example project showing 30 annotations used

E) Full table (Annotation | Purpose | Example)

Just reply with: A / B / C / D / E 😄

A and E

Awesome choice, Pawan 😎

Here is:

wise)

✅ A) Spring Boot Annotations – Cheat Sheet (Category-

and

✅ E) Full Table (Annotation | Purpose | Example)

You can copy this and I can convert it into a PDF for you next if you say:

👉 “Convert this into PDF”

Copy code

🅐 Spring Boot Annotation Cheat Sheet 📄

🔹 Core & IOC

less

@Component, @Service, @Repository, @Controller, @RestController

@Configuration, @Bean, @ComponentScan

@Autowired, @Qualifier, @Primary

@Value, @PropertySource

@Profile, @Scope, @Lazy, @DependsOn

🔹 Spring Boot

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 9/2417/02/2026, 16:47 less

Spring Boot Annotations List

Copy code

@SpringBootApplication

@EnableAutoConfiguration

@ConfigurationProperties

@EnableConfigurationProperties

@SpringBootTest

@TestConfiguration

@MockBean, @SpyBean

🔹 Web / REST

less

@RequestMapping

@GetMapping, @PostMapping, @PutMapping, @DeleteMapping, @PatchMapping

Copy code

@RequestParam, @PathVariable

@RequestBody, @ResponseBody

@ResponseStatus

@RequestHeader, @CookieValue

@ModelAttribute

@CrossOrigin

🔹 Exception Handling

less

@ExceptionHandler

@ControllerAdvice

@RestControllerAdvice

Copy code

🔹 Validation

less

Copy code

@Valid, @Validated

@NotNull, @NotEmpty, @NotBlank

@Size, @Min, @Max

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 10/2417/02/2026, 16:47 @Email, @Pattern

@Positive, @Negative

@Future, @Past

@Digits

Spring Boot Annotations List

🔹 JPA / Hibernate

less

@Entity, @Table

@Id, @GeneratedValue

@Column, @Transient, @Lob

@OneToOne, @OneToMany, @ManyToOne, @ManyToMany

@JoinColumn, @JoinTable

@Embedded, @Embeddable

@Enumerated, @Temporal

Copy code

🔹 Spring Data

less

@Repository

@EnableJpaRepositories

@Query

@Modifying

@Param

@Transactional

Copy code

🔹 Security

less

@EnableWebSecurity

@EnableMethodSecurity

@PreAuthorize

@PostAuthorize

@Secured

Copy code

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 11/2417/02/2026, 16:47 @RolesAllowed

@AuthenticationPrincipal

Spring Boot Annotations List

🔹 Scheduling & Async

less

Copy code

@EnableScheduling

@Scheduled

@EnableAsync

@Async

🔹 Cache

less

Copy code

@EnableCaching

@Cacheable

@CachePut

@CacheEvict

@Caching

🔹 Messaging

less

Copy code

@KafkaListener

@EnableKafka

@JmsListener

@EnableJms

@RabbitListener

@RabbitHandler

🔹 Spring Cloud

less

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 12/2417/02/2026, 16:47 Spring Boot Annotations List

Copy code

@EnableDiscoveryClient

@FeignClient

@EnableFeignClients

@LoadBalanced

@RefreshScope

@Retryable

@Recover

🔹 AOP

less

@Aspect

@Before

@After

@AfterReturning

@AfterThrowing

@Around

@Pointcut

@EnableAspectJAutoProxy

Copy code

🔹 Testing

less

@RunWith / @ExtendWith

@Test

@SpringBootTest

@WebMvcTest

@DataJpaTest

@MockBean

@AutoConfigureMockMvc

@TestPropertySource

@ActiveProfiles

@DirtiesContext

@BeforeEach, @AfterEach

Copy code

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 13/2417/02/2026, 16:47 🔹 Actuator

less

Spring Boot Annotations List

@Endpoint

@ReadOperation

@WriteOperation

@DeleteOperation

Copy code

🅔 Full Table: Annotation | Purpose | Example

Annotation Purpose Example

Copy code

@SpringBootApplicatio

Main entry point @SpringBootApplication public

class App {}

@Component Generic bean @Component class MyBean {}

@Service Business logic layer @Service class UserService {}

@Repository DAO layer @Repository interface UserRepo

{}

@RestControllerREST controller @RestController class

UserController {}

@Autowired Inject dependency @Autowired UserService service;

@Bean Create bean manually @Bean DataSource ds()

@Configuration Config class @Configuration class AppConfig

{}

@GetMapping HTTP GET @GetMapping("/users")

@PostMapping HTTP POST @PostMapping("/users")

@RequestBodyMap JSON to object public save(@RequestBody User u)

@PathVariable U

L variable @PathVariable int id

@RequestParam Query param @RequestParam String name

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 14/2417/02/2026, 16:47 Spring Boot Annotations List

Annotation Purpose Example

@ResponseStatus Custom HTTP status @ResponseStatus(HttpStatus.OK)

@ExceptionHandler Handle exception @ExceptionHandler(Exception.clas

@ControllerAdvice Global exception

handler

@ControllerAdvice class GlobalEx

{}

@Entity JPA entity @Entity class User {}

@Id Primary key @Id Long id;

@GeneratedValue Auto PK @GeneratedValue(strategy=AUTO)

@OneToManyRelationship @OneToMany List<Order>

@ManyToOneRelationship @ManyToOne User user

@JoinColumn FK column @JoinColumn(name="user_id")

@Query Custom query @Query("select u from User u")

@Transactional Transaction mgmt @Transactional public void

save()

@Valid Trigger validation public save(@Valid User u)

@NotNull Field validation @NotNull String name;

@EnableScheduling Enable scheduler @EnableScheduling

@Scheduled Cron job @Scheduled(cron="0 0 * * *")

@EnableAsync Enable async @EnableAsync

@AsyncR

un async @Async public void task()

@Cacheable Cache result @Cacheable("users")

@PreAuthorize Security rule @PreAuthorize("hasRole('ADMIN')"

)

@FeignClientREST client @FeignClient("order-service")

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 15/2417/02/2026, 16:47 Spring Boot Annotations List

Annotation Purpose Example

@Aspect AOP class @Aspect class LogAspect {}

@Before Before advice @Before("execution(*)")

@Test Unit test @Test void testSave()

@SpringBootTest Full context test @SpringBootTest class TestApp {}

@MockBeanMock bean @MockBean UserService service;

@Endpoint Actuator endpoint @Endpoint(id="custom")

🎁 Next Step (Free Bonus)

I can generate for you:

✅ PDF Cheat Sheet

✅ Excel table (Annotation | Purpose | Example)

✅ Printable A4 sheet

✅ Mind map diagram

Just reply one word:

PDF or EXCEL or DIAGRAM or ALL

And I’ll generate it for you 🚀

category-wise give me annotation list

Got it 👍 You

want a pure category-wise list of Spring Boot / Spring annotations (no

explanations, no examples — just clean grouped lists).

Here is the most complete practical catalog used in real Spring Boot applications.

🟢 1. Core / IOC / Bean Management

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 16/2417/02/2026, 16:47 Spring Boot Annotations List

@Component

@Service

@Repository

@Controller

@RestController

@Configuration

@Bean

@ComponentScan

@Import

@ImportResource

@DependsOn

@Lazy

@Scope

@Primary

@Qualifier

@Profile

@PropertySource

@Value

@Autowired

@Required

@Lookup

🟢 2. Spring Boot Specific

@SpringBootApplication

@EnableAutoConfiguration

@AutoConfiguration

@ConfigurationProperties

@EnableConfigurationProperties

@ConstructorBinding

@SpringBootConfiguration

@TestConfiguration

@SpringBootTest

@MockBean

@SpyBean

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 17/2417/02/2026, 16:47 Spring Boot Annotations List

🟢 3. Web / MVC / REST

Mapping

@RequestMapping

@GetMapping

@PostMapping

@PutMapping

@DeleteMapping

@PatchMapping

Request / Response

@RequestParam

@PathVariable

@RequestBody

@ResponseBody

@ResponseStatus

@RequestHeader

@CookieValue

@ModelAttribute

@MatrixVariable

@CrossOrigin

Exception

@ExceptionHandler

@ControllerAdvice

@RestControllerAdvice

🟢 4. Validation (Jakarta / Hibernate Validator)

@Valid

@Validated

@NotNull

@NotEmpty

@NotBlank

@Size

@Min

@Max

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 18/2417/02/2026, 16:47 Spring Boot Annotations List

@Positive

@Negative

@Email

@Pattern

@Future

@Past

@Digits

@AssertTrue

@AssertFalse

🟢 5. Persistence / JPA / Hibernate

Entity

@Entity

@Table

@Id

@GeneratedValue

@Column

@Transient

@Lob

@Enumerated

@Temporal

@Version

Relations

@OneToOne

@OneToMany

@ManyToOne

@ManyToMany

@JoinColumn

@JoinTable

@MapsId

@MapKey

@OrderBy

@OrderColumn

@Embedded

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 19/2417/02/2026, 16:47 Spring Boot Annotations List

@Embeddable

🟢 6. Spring Data

@Repository

@EnableJpaRepositories

@Query

@NamedQuery

@NamedNativeQuery

@Modifying

@Param

@Procedure

@Transactional

@Lock

@EntityGraph

🟢 7. Transaction Management

@Transactional

@EnableTransactionManagement

🟢 8. Security (Spring Security)

@EnableWebSecurity

@EnableMethodSecurity

@Secured

@RolesAllowed

@PreAuthorize

@PostAuthorize

@PreFilter

@PostFilter

@AuthenticationPrincipal

🟢 9. Scheduling & Async

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 20/2417/02/2026, 16:47 Spring Boot Annotations List

@EnableScheduling

@Scheduled

@EnableAsync

@Async

🟢 10. Cache

@EnableCaching

@Cacheable

@CachePut

@CacheEvict

@Caching

🟢 11. AOP

@Aspect

@Before

@After

@AfterReturning

@AfterThrowing

@Around

@Pointcut

@EnableAspectJAutoProxy

🟢 12. Messaging (Kafka / JMS / RabbitMQ)

@EnableKafka

@KafkaListener

@SendTo

@EnableJms

@JmsListener

@RabbitListener

@RabbitHandler

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 21/2417/02/2026, 16:47 Spring Boot Annotations List

🟢 13. Spring Cloud / Microservices

@EnableDiscoveryClient

@EnableEurekaClient

@FeignClient

@EnableFeignClients

@LoadBalanced

@RefreshScope

@Retryable

@Recover

@CircuitBreaker

🟢 14. Conditional (Auto Configuration)

@Conditional

@ConditionalOnBean

@ConditionalOnMissingBean

@ConditionalOnProperty

@ConditionalOnClass

@ConditionalOnMissingClass

@ConditionalOnWebApplication

@ConditionalOnNotWebApplication

@ConditionalOnExpression

🟢 15. Actuator

@Endpoint

@ReadOperation

@WriteOperation

@DeleteOperation

@EndpointWebExtension

🟢 16. Internationalization / Formatting

@DateTimeFormat

@NumberFormat

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 22/2417/02/2026, 16:47 Spring Boot Annotations List

🟢 17. Testing

@RunWith

@ExtendWith

@Test

@BeforeEach

@AfterEach

@BeforeAll

@AfterAll

@SpringBootTest

@WebMvcTest

@DataJpaTest

@JdbcTest

@JsonTest

@RestClientTest

@AutoConfigureMockMvc

@AutoConfigureTestDatabase

@TestPropertySource

@ActiveProfiles

@DirtiesContext

⚠ Note:

There is no official single list of “every annotation” because Spring = multiple

frameworks + Jakarta EE + Spring Cloud + Testing + new

versions.

This list covers 95% of annotations used in enterprise Spring Boot projects.

If you

want, next I can give you this in:

✅ PDF cheat sheet

✅ Excel sheet

✅ Mind map diagram

✅ Top 50 most important annotations only

✅ Module-wise (spring-core, spring-web, spring-data, spring-security) list

Just say which one: PDF / EXCEL / DIAGRAM / TOP50 / M

ODULE-WISE

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 23/2417/02/2026, 16:47 Spring Boot Annotations List

https://chatgpt.com/c/69944d3b-e6c4-83a3-bde2-f701e83c8151 24/24

Monday, 24 August 2026

kubernetes commands.

Tuesday, 18 August 2026

Data dog data flow

Sunday, 3 May 2026

squash and merge

🔹 Step-by-step (squash your 5 commits into 1)

1. Go to your branch

2. Start interactive rebase (last 5 commits)

3. You’ll see something like:

4. Change it to:

5. Save & close editor

6. Done 🎉

🔹 Important (don’t skip this)

🔹 Shortcut (if you don’t care about messages)

🔹 Pro tip (real-world)

🔹 Simple Meaning

🔹 Step-by-step explanation

✅ git reset --soft HEAD~5

✅ git commit -m "..."

🔹 Visual understanding

Before:

After reset:

After new commit:

🔹 Key difference vs rebase

🔹 Important warning ⚠️

🔹 One-line understanding

Tuesday, 28 April 2026

AWS S3 bucket tier.

Wednesday, 15 April 2026

Open API documentation

Wednesday, 18 March 2026

Design pattern

🧠 First: What is a Design Pattern?

🧩 3 Types of Design Patterns

1. 🏗️ Creational (Object banana ka tareeka)

2. 🧱 Structural (Object ko kaise jode)

3. 🔄 Behavioral (Object kaise behave kare)

🏗️ 1. CREATIONAL PATTERNS (Creation)

1. Singleton 🧍

🍋 Lemon Example:

💻 Java Example:

🔥 Real Use:

2. Factory 🏭

🍋 Example:

💻 Java Example:

🔥 Real Use:

3. Builder 🧱

🍋 Example:

💻 Example:

🔥 Real Use:

🧱 2. STRUCTURAL PATTERNS

4. Adapter 🔌

🍋 Example:

💻 Example:

🔥 Real Use:

5. Decorator 🎁

🍋 Example:

💻 Example:

🔥 Real Use:

6. Facade 🏢

🍋 Example:

💻 Example:

🔥 Real Use:

🔄 3. BEHAVIORAL PATTERNS

7. Strategy 🎯

🍋 Example:

💻 Example:

🔥 Real Use:

8. Observer 👀

🍋 Example:

💻 Example:

🔥 Real Use:

9. Command 📦

🍋 Example:

💻 Example:

🔥 Real Use:

🚀 Most Important for YOU (Based on your work)

🎯 Simple Memory Trick

💡 Real-world Example (Your Project)

✅ `git reset --soft HEAD~5`

✅ `git commit -m "..."`