#GIT

Last updated    - V6 (17-Sep-2025)

Key Concepts

Topic	SubTopic	Basic	Intermediate	Advanced	Expert
Introduction	What is Git, Version Control concepts, Git vs SVN	✅	✅	✅	✅
Installation & Setup	Install Git, Initial configuration, SSH keys	✅	✅	✅	✅
Core Concepts	Repository, Working directory, Staging area	✅	✅	✅	✅
Basic Commands	git init, git clone, git add, git commit, git status, git log	✅	✅	✅	✅
Branching	git branch, git checkout, git switch, git merge	✅	✅	✅	✅
Remote Repositories	git remote, git fetch, git pull, git push	✅	✅	✅	✅
Collaboration	Forking, Pull requests, Code review workflow		✅	✅	✅
Merging & Conflicts	Merge strategies, Conflict resolution, Rebase basics		✅	✅	✅
Stashing & Cleaning	git stash, git clean, temporary changes		✅	✅	✅
Advanced Branching	git rebase, cherry-pick, revert, reset			✅	✅
Tags & Releases	Annotated tags, Lightweight tags, Versioning	✅	✅	✅	✅
Undo & Recovery	git reflog, reset, revert, checkout recovery		✅	✅	✅
Git Internals	Object model, Blobs, Trees, Commits, SHA-1			✅	✅
Hooks & Customization	Git hooks, Aliases, Custom configs			✅	✅
Performance & Scaling	Large repos, Git LFS, Submodules, Monorepos			✅	✅
Security	GPG commit signing, Credential management		✅	✅	✅
CI/CD Integration	GitHub Actions, GitLab CI, Jenkins with Git		✅	✅	✅
Best Practices	Commit message guidelines, Branch strategy (GitFlow, trunk-based), Code reviews	✅	✅	✅	✅
Tools & GUIs	GitHub Desktop, SourceTree, GitKraken, IDE plugins	✅	✅	✅	✅
Troubleshooting	Common errors, Detached HEAD, Merge issues, Debugging history		✅	✅	✅

Interview question

1. Git Basics

1. What is Git, and why is it used?
2. What is the difference between Git and other VCS like SVN?
3. Explain the difference between a repository, a working directory, and a staging area.
4. How do you initialize a new Git repository?
5. How do you clone a repository?
6. What does git add do?
7. What does git commit do?
8. What is the difference between git commit -m and git commit -a?
9. What is the difference between git status and git log?
10. Explain the difference between git fetch and git pull.
11. What does git push do?
12. How do you check the current Git configuration?
13. How do you create a .gitignore file?
14. How do you check the version of Git installed?
15. What is the difference between a bare repository and a non-bare repository?
16. How do you rename a Git branch locally?
17. What does HEAD mean in Git?
18. How do you delete a branch in Git locally?
19. How do you delete a branch in Git remotely?
20. How do you configure a global username and email in Git?

---

2. Branching & Merging

1. What is a branch in Git?
2. How do you create a branch in Git?
3. How do you switch between branches?
4. What is the difference between git checkout and git switch?
5. How do you list all branches in Git?
6. How do you rename a branch?
7. How do you merge one branch into another?
8. What is a fast-forward merge?
9. What is a three-way merge?
10. What are merge conflicts in Git?
11. How do you resolve merge conflicts?
12. What is the difference between merge and rebase?
13. What does git cherry-pick do?
14. How do you undo a merge?
15. What is the difference between git reset and git revert?
16. How do you create a tracking branch?
17. What is the purpose of git branch -vv?
18. What is a detached HEAD state?
19. How do you move a commit from one branch to another?
20. Explain GitFlow branching strategy.

---

3. Remote Repositories

1. What is a remote in Git?
2. How do you add a remote repository?
3. How do you list all remotes in Git?
4. How do you remove a remote repository?
5. How do you rename a remote repository?
6. What does origin mean in Git?
7. How do you fetch changes from a remote without merging?
8. What is the difference between git fetch and git pull?
9. How do you push changes to a remote branch?
10. How do you push a new local branch to a remote repository?
11. How do you set a default remote branch for pushing?
12. How do you track a remote branch locally?
13. What is the purpose of git remote -v?
14. How do you force push changes in Git?
15. What are the risks of git push --force?
16. How do you safely force push without overwriting others? changes?
17. How do you delete a branch in a remote repository?
18. How do you check if a branch exists in a remote repo?
19. What is a fork in Git, and how is it different from a clone?
20. How do you sync a fork with the upstream repository?

---

4. Staging, Stash & Clean

1. What is the staging area in Git?
2. How do you add files to the staging area?
3. How do you remove files from the staging area?
4. What does git diff do?
5. What does git diff --staged show?
6. How do you unstage a file?
7. What is Git stash?
8. How do you stash changes?
9. How do you apply stashed changes?
10. How do you list all stashes?
11. How do you drop a stash?
12. How do you clear all stashes?
13. How do you apply a stash without removing it?
14. How do you stash untracked files?
15. What is the difference between git stash pop and git stash apply?
16. What does git clean do?
17. How do you remove untracked files in Git?
18. How do you remove ignored files in Git?
19. What is the difference between tracked and untracked files?
20. How do you check which files are ignored in Git?

---

5. Undo & Recovery

1. How do you undo the last commit?
2. What does git reset do?
3. Difference between git reset --soft, --mixed, and --hard.
4. How do you revert a commit?
5. What does git reflog do?
6. How do you recover a deleted branch?
7. How do you find a lost commit in Git?
8. What is an orphan branch?
9. How do you go back to a previous commit?
10. What is the difference between git reset HEAD^ and git reset --hard HEAD^?
11. How do you undo changes to a file before staging?
12. How do you undo changes to a file after staging?
13. How do you remove the last commit without deleting changes?
14. How do you squash commits?
15. How do you amend the last commit message?
16. How do you move commits to another branch?
17. How do you recover a commit after rebase?
18. What is the difference between git checkout and git restore?
19. How do you discard all local changes in Git?
20. What is the difference between git reset and git checkout?

---

6. Git Internals

1. Explain the Git object model.
2. What are blobs, trees, and commits in Git?
3. What is the purpose of SHA-1 in Git?
4. Where does Git store its data?
5. What is .git directory?
6. What are Git references?
7. What is HEAD in Git?
8. What is a Git object hash?
9. How does Git ensure data integrity?
10. Explain the concept of Git snapshots vs diffs.
11. What is the difference between Git index and working tree?
12. What is a packed object in Git?
13. What is git gc?
14. What is the purpose of git fsck?
15. How does Git compress objects?
16. Explain Git pack files.
17. What is git cat-file used for?
18. What is git hash-object?
19. How does Git handle large files?
20. Explain Git internals vs Git commands.

---

7. Collaboration & Workflow

1. What is a pull request?
2. What is the difference between a pull request and a merge request?
3. How do you create a pull request in GitHub?
4. What is the purpose of code reviews in Git workflows?
5. What is GitHub flow?
6. What is GitLab flow?
7. What is trunk-based development?
8. Explain feature branching workflow.
9. Explain release branching workflow.
10. What is the GitFlow workflow?
11. What is the difference between GitHub flow and GitFlow?
12. What is a hotfix branch?
13. What is a long-lived branch?
14. What is the difference between main and master branch?
15. How do you enforce branch protection rules?
16. How do you enforce commit message guidelines?
17. How do you squash commits in a pull request?
18. How do you rebase a pull request?
19. How do you resolve conflicts in a pull request?
20. How do you maintain a clean Git history?

---

8. Advanced Commands & Techniques

1. What does git bisect do?
2. How do you use git bisect to find a bug?
3. What does git blame do?
4. How do you use git blame effectively?
5. What does git shortlog do?
6. What does git describe do?
7. What does git rev-parse do?
8. What does git show do?
9. What does git archive do?
10. What is git bundle?
11. How do you split a commit into multiple commits?
12. How do you combine multiple commits into one?
13. How do you sign a commit with GPG?
14. What does git verify-commit do?
15. What does git verify-tag do?
16. What does git notes do?
17. What is the difference between git submodule and git subtree?
18. How do you add a Git submodule?
19. How do you update a Git submodule?
20. How do you remove a Git submodule?

---

9. CI/CD Integration

1. How do you integrate Git with Jenkins?
2. What is GitHub Actions?
3. How do you trigger a pipeline from a Git commit?
4. What is the difference between webhooks and polling?
5. How do you use Git in a Jenkins pipeline?
6. How do you automate tests with GitHub Actions?
7. How do you deploy code using GitLab CI?
8. What is the difference between GitHub Actions and GitLab CI?
9. How do you use Git tags in CI/CD pipelines?
10. What is the role of Git in DevOps?
11. How do you enforce code quality checks in Git workflows?
12. How do you rollback a deployment using Git?
13. How do you use Git in Kubernetes deployments?
14. What is GitOps?
15. How do you implement GitOps?
16. What tools are used for GitOps?
17. How do you automate semantic versioning with Git?
18. How do you use Git for continuous delivery?
19. What are GitHub Packages?
20. What is the difference between GitHub Packages and Artifactory?

---

10. Security & Best Practices

1. How do you sign commits in Git?
2. What is the importance of signed commits?
3. How do you verify a signed commit?
4. How do you securely store Git credentials?
5. What is the use of Git credential helper?
6. How do you rotate Git credentials?
7. What is the difference between HTTPS and SSH for Git?
8. How do you enforce branch policies in GitHub?
9. What is the principle of least privilege in Git access control?
10. How do you prevent accidental force pushes?
11. How do you prevent committing secrets to Git?
12. What is Git-secrets tool?
13. What is pre-commit hook?
14. What is the difference between client-side and server-side hooks?
15. How do you use Git hooks for code quality enforcement?
16. How do you enforce commit message conventions?
17. How do you maintain a clean commit history?
18. How do you choose a branching strategy for a project?
19. What are common Git anti-patterns?
20. What are Git best practices for large teams?

Related Topics

#Spring_Framework

Last updated    - V6 (22-Sep-2025)

Key Concepts

Topic	Sub-Topics (comma separated)	Basic	Intermediate	Advanced	Expert
Core Container	Beans, BeanFactory, ApplicationContext, Bean Scopes, Bean Lifecycle, Dependency Injection (DI), Inversion of Control (IoC)	✅	✅	✅	✅
Configuration	XML Configuration, Java-based Configuration, Annotation-based Configuration, Environment Profiles, Externalized Configuration	✅	✅	✅	✅
Spring Context	ApplicationContext, MessageSource, Internationalization (i18n), Event Handling, ApplicationListener	✅	✅	✅	✅
Spring AOP	AOP Concepts, Join Points, Pointcuts, Advice, Aspects, Proxying, AspectJ Integration		✅	✅	✅
Data Access (DAO)	JDBC Template, DataSource, Transaction Management, Exception Translation, ORM Integration		✅	✅	✅
Spring ORM	Hibernate Integration, JPA Support, EntityManager, SessionFactory, Transactional Annotations		✅	✅	✅
Spring Transactions	Programmatic Transactions, Declarative Transactions, Propagation, Isolation Levels, Rollback Rules		✅	✅	✅
Spring MVC	DispatcherServlet, Controllers, HandlerMapping, ViewResolver, ModelAndView, Form Handling, Validation	✅	✅	✅	✅
Spring REST	REST Controllers, @RestController, @RequestBody, @ResponseBody, Content Negotiation, Exception Handling		✅	✅	✅
Spring WebFlux	Reactive Programming, Mono, Flux, Functional Endpoints, Reactive Repositories			✅	✅
Spring Security	Authentication, Authorization, Security Filters, UserDetailsService, Password Encoding, JWT, OAuth2		✅	✅	✅
Spring Boot	Auto-Configuration, Starters, Actuator, Spring Boot CLI, Spring Initializr, Properties & YAML	✅	✅	✅	✅
Spring Data	Spring Data JPA, Spring Data MongoDB, PagingAndSortingRepository, CrudRepository, Custom Queries		✅	✅	✅
Spring Cloud	Config Server, Eureka, Zuul/Gateway, Ribbon, Feign, Hystrix, Sleuth, Cloud Bus			✅	✅
Spring Batch	Job, Step, Tasklet, ItemReader, ItemWriter, JobLauncher, Retry & Skip Logic			✅	✅
Spring Integration	Messaging, Channels, Transformers, Routers, Adapters, Gateways, Enterprise Integration Patterns			✅	✅
Spring Testing	Unit Testing with JUnit, MockMvc, @SpringBootTest, Test Slices, Embedded Database Testing	✅	✅	✅	✅
Spring Messaging	JMS, AMQP, STOMP, WebSockets, MessageConverters, RabbitMQ/Kafka Integration			✅	✅
Spring Reactive	Reactive Streams, Reactive Data Access, Backpressure, Reactor Core, WebFlux Security			✅	✅
Spring GraphQL	Spring for GraphQL, DataFetchers, Schema Mapping, Subscriptions, GraphQL + WebFlux			✅	✅

Interview question

1. Introduction & Basics

1. What is AOP (Aspect-Oriented Programming)?
2. What are the advantages of using AOP?
3. Difference between AOP and OOP.
4. What are typical use cases of AOP?
5. How does AOP help in modularizing cross-cutting concerns?
6. What are cross-cutting concerns?
7. Difference between core Spring and Spring AOP.
8. What is the difference between static and dynamic AOP?
9. What is weaving in AOP?
10. Difference between compile-time and runtime weaving.

---

2. Core Concepts

1. What is an Aspect in Spring AOP?
2. What is a Join point?
3. What is Advice in Spring AOP?
4. What is a Pointcut?
5. What is Introduction in AOP?
6. Difference between Aspect, Advice, and Pointcut.
7. What is a Target object?
8. How is a Proxy related to Spring AOP?
9. What are the types of Join points in Spring?
10. What is AspectJ and its relation to Spring AOP?

---

3. Types of Advice

1. What is Before Advice?
2. What is After Advice?
3. What is AfterReturning Advice?
4. What is AfterThrowing Advice?
5. What is Around Advice?
6. Difference between Before and Around Advice.
7. How to implement custom logic in Around Advice?
8. How to access method arguments in Advice?
9. How to modify return value in AfterReturning Advice?
10. How to handle exceptions in AfterThrowing Advice?

---

4. Pointcut Expressions

1. What is a Pointcut Expression?
2. How to use execution() in pointcut expressions?
3. How to use within() in pointcut expressions?
4. How to use args() in pointcut expressions?
5. How to use @annotation() in pointcut expressions?
6. How to use bean() in pointcut expressions?
7. Difference between execution() and within().
8. How to combine multiple pointcut expressions?
9. How to create reusable pointcut expressions?
10. How to test pointcut expressions?

---

5. Aspect Implementation

1. What is @Aspect annotation used for?
2. How to use @Before annotation?
3. How to use @After annotation?
4. How to use @Around annotation?
5. How to use @AfterReturning annotation?
6. How to use @AfterThrowing annotation?
7. How to inject dependencies into an Aspect?
8. How to order aspects using @Order?
9. Difference between XML-based and annotation-based aspects.
10. How to define multiple advices in a single aspect?

---

6. Weaving

1. What is weaving in AOP?
2. Difference between compile-time, load-time, and runtime weaving.
3. How does Spring implement runtime weaving?
4. How to enable load-time weaving in Spring?
5. What are AspectJ weaver and proxy-based weaving?
6. How to debug issues in weaving?
7. Difference between proxy-based AOP and AspectJ AOP.
8. How does Spring choose JDK Dynamic Proxy vs CGLIB?
9. How to force CGLIB proxy in Spring?
10. How does AOP proxy affect class hierarchy?

---

7. Spring AOP Proxy

1. What is a proxy in Spring AOP?
2. Difference between JDK Dynamic Proxy and CGLIB Proxy.
3. How does Spring decide which proxy to use?
4. How to access the underlying target object?
5. How does proxy affect equals() and hashCode()?
6. How to apply multiple advices on a single proxy?
7. How to test proxy objects?
8. How to handle self-invocation in proxies?
9. Difference between interface-based and class-based proxy.
10. How to use ProxyFactoryBean?

---

8. Order & Precedence

1. How to order multiple aspects using @Order annotation?
2. How does Spring determine execution order of advices?
3. Difference between global and local aspect order.
4. How to set priority for specific advices?
5. How to debug advice execution order?
6. How to apply conditional advice execution?
7. How to combine multiple pointcuts with order?
8. How to prevent circular advice calls?
9. How to test order in unit tests?
10. How to document execution order of aspects?

---

9. Exception Handling

1. How to handle exceptions in AOP advice?
2. How to propagate exceptions from Advice?
3. How to implement retry logic in Around Advice?
4. How to implement fallback methods in Advice?
5. How to log exceptions centrally using AOP?
6. How to combine exception handling and transaction management?
7. How to prevent exception swallowing in advices?
8. How to implement custom exception hierarchies in AOP?
9. How to test exception handling in aspects?
10. How to use @AfterThrowing to notify external systems?

---

10. Integration & Advanced Topics

1. How to integrate Spring AOP with Spring Boot?
2. How to use AOP for logging method execution time?
3. How to implement security using AOP?
4. How to implement caching using AOP?
5. How to profile applications using AOP?
6. How to use AOP with transactions?
7. How to implement custom annotations for aspects?
8. How to test AOP in integration tests?
9. What are best practices for writing aspects?
10. Common pitfalls when using Spring AOP.

---

Related Topics

Spring_Boot

Spring_Framework

Spring_Cloud

Spring_Rest

Spring_AOP

Spring_Batch

Spring_MVC

Spring_Security

Spring_JPA

Spring_AI

#Solace

Last updated    - V6 (03-Oct-2025)

Key Concepts

Topic	Sub-Topics	Basic	Intermediate	Advanced	Expert
Introduction	What is Solace, Messaging patterns, Pub/Sub, Queueing, Use cases	✅	✅
Architecture	Solace Message Broker, Components, Clustering, Redundancy	✅	✅	✅
Messaging Concepts	Topics, Queues, Subscriptions, Durable/Non-durable, Guaranteed vs Direct	✅	✅	✅	✅
Producers	Publishing messages, QoS levels, Message properties, API usage	✅	✅	✅	✅
Consumers	Receiving messages, Subscriptions, Queue handling, Event-driven consumption	✅	✅	✅	✅
APIs & SDKs	Solace Java API, JMS API, REST API, MQTT support	✅	✅	✅	✅
Administration	Broker configuration, VPNs, Users & ACLs, Monitoring	✅	✅	✅	✅
Security	Authentication, Authorization, Encryption, ACLs, TLS/SSL	✅	✅	✅	✅
High Availability	Active/Standby, HA clusters, Disaster recovery		✅	✅	✅
Performance & Tuning	Message throughput, Latency optimization, Resource tuning		✅	✅	✅
Advanced Features	Message replay, Guaranteed delivery, Transactional messaging, Event broker routing		✅	✅	✅
Monitoring & Logging	System monitoring, Metrics, Tracing, Alerting	✅	✅	✅	✅
Integration	Microservices, Spring Boot integration, Cloud deployment	✅	✅	✅	✅
Troubleshooting	Common issues, Debugging, Error handling, Logs analysis	✅	✅	✅	✅
Best Practices	Message design, Queue/topic design, Scaling, Security practices	✅	✅	✅	✅

Interview question

Basic

1. What is Solace PubSub+ and what problems does it solve?
2. Explain the difference between queues and topics in Solace.
3. What is a message VPN in Solace?
4. How does Solace support point-to-point messaging?
5. What is publish-subscribe messaging in Solace?
6. Define persistent vs. non-persistent messaging in Solace.
7. What is the role of a client profile in Solace?
8. What is guaranteed delivery in Solace messaging?
9. Explain the difference between direct and guaranteed messages.
10. How do you connect to a Solace broker?
11. What is a Solace session?
12. Explain Solace message acknowledgment modes.
13. What is Solace CLI used for?
14. Define message spooling in Solace.
15. How do you create a queue in Solace?
16. What is the difference between a durable and a non-durable subscription?
17. What protocols are supported by Solace PubSub+?
18. What is the role of the default VPN?
19. How do you publish a message using Solace JCSMP API?
20. What are the basic security features available in Solace?
21. Explain Solace connection retries.
22. What is the role of message TTL (time-to-live)?
23. How do you monitor a Solace broker?
24. What is SolAdmin?
25. What is the difference between static and dynamic subscriptions?

Intermediate

1. Explain topic hierarchy and wildcards in Solace.
2. What are durable topic endpoints (DTE)?
3. How does Solace handle flow control?
4. Explain client-acknowledge mode in Solace.
5. What is the role of replay in Solace PubSub+?
6. How does Solace support load balancing across consumers?
7. What are selectors in Solace queues?
8. How does Solace guarantee once-and-only-once delivery?
9. Explain how Solace supports message filtering.
10. What is Solace JCSMP API and how is it used?
11. How do you configure client authentication in Solace?
12. What is an ACL profile in Solace?
13. How do you configure TLS/SSL for Solace?
14. Explain Solace event broker scaling options.
15. How do you create topic subscriptions in Solace?
16. What is the difference between Solace software broker and appliance?
17. How does Solace support REST-based messaging?
18. What is Solace Spring Cloud Stream binder?
19. How do you use MQTT with Solace?
20. What is Solace?s integration with Apache Kafka?
21. Explain message compression in Solace.
22. How does Solace handle dead message queues (DMQ)?
23. What is Solace?s event mesh?
24. What are Solace?s persistent stores used for?
25. How do you trace a message path in Solace?

Advanced

1. Explain Solace HA architecture.
2. How does Solace implement disaster recovery (DR)?
3. What is a replication bridge in Solace?
4. How do you configure message replay for compliance use cases?
5. What is a multi-node Solace deployment?
6. Explain Solace?s multi-protocol support in a real use case.
7. What are the performance tuning options for Solace appliances?
8. How does Solace ensure zero message loss during failover?
9. What is Solace?s distributed tracing support?
10. Explain the difference between HA and DR in Solace.
11. How does Solace handle back-pressure in high throughput scenarios?
12. What is Solace?s guaranteed messaging store and how does it scale?
13. How do you secure Solace in a multi-tenant environment?
14. Explain Solace PubSub+ Cloud architecture.
15. How do you integrate Solace with cloud-native platforms like Kubernetes?
16. What is the role of Solace REST Delivery Points (RDP)?
17. How does Solace provide interoperability between legacy MQ and cloud-native apps?
18. Explain Solace?s integration with Apache Pulsar or RabbitMQ.
19. How does Solace handle schema evolution in messages?
20. Explain best practices for designing Solace topic hierarchy.
21. How do you optimize message replay performance?
22. What are Solace?s bridging capabilities across multiple data centers?
23. How does Solace enable geo-replication?
24. How do you implement message partitioning in Solace?
25. What are the limits of message size and throughput in Solace?

Expert

1. Design a Solace architecture for global financial trading.
2. How would you migrate from Tibco EMS or IBM MQ to Solace?
3. Explain in detail how Solace implements event-driven microservices.
4. How do you debug performance bottlenecks in Solace clusters?
5. How would you implement event sourcing using Solace replay?
6. Explain hybrid-cloud messaging with Solace.
7. How does Solace handle regulatory compliance requirements (MiFID II, etc.)?
8. What are Solace?s advanced monitoring and observability tools?
9. How would you secure Solace against DDoS attacks?
10. How do you scale Solace in a high-frequency trading system?
11. Explain message deduplication strategies in Solace.
12. How does Solace compare with Apache Kafka in enterprise use cases?
13. Design a DR strategy for a Solace-based architecture spanning regions.
14. How would you tune Solace for ultra-low latency applications?
15. Explain message routing optimization in Solace event mesh.
16. What are the trade-offs between direct messaging and guaranteed messaging in enterprise use cases?
17. How do you integrate Solace with event-driven APIs?
18. How do you ensure observability of Solace in a multi-cloud environment?
19. What is Solace?s role in OpenTelemetry?
20. Explain the impact of schema registry with Solace integration.
21. How would you implement an IoT solution using Solace PubSub+?
22. What are the most challenging troubleshooting issues in Solace production systems?
23. How do you evaluate Solace vs. Confluent Kafka for a given use case?
24. How would you implement a secure multi-tenant SaaS messaging system on Solace?
25. Explain Solace?s future roadmap in the context of event-driven architecture.

Related Topics

#MQTT

Last updated    - V6 (03-Oct-2025)

Key Concepts

Topic	SubTopic	Basic ✅	Intermediate ✅	Advanced ✅	Expert ✅
Introduction	What is MQTT, Features, Advantages, Use cases	✅	✅	✅	✅
MQTT vs HTTP	Differences, Performance, Use cases	✅	✅	✅	✅
Architecture	Broker, Clients, Publish/Subscribe model	✅	✅	✅	✅
QoS Levels	QoS 0, QoS 1, QoS 2, Message delivery guarantees	✅	✅	✅	✅
Topics & Subscriptions	Topic structure, Wildcards, Hierarchies	✅	✅	✅	✅
Messages	Payload, Retained messages, Duplicate messages	✅	✅	✅	✅
MQTT Broker	Popular brokers, Configuration, Scalability	✅	✅	✅	✅
MQTT Client	Libraries, Connecting, Subscribing, Publishing	✅	✅	✅	✅
Security	Authentication, Authorization, TLS/SSL, Certificates		✅	✅	✅
MQTT with IoT	Integration with IoT devices, Sensors, Real-time updates	✅	✅	✅	✅
Persistent Session	Session state, Clean session, Durable subscriptions		✅	✅	✅
Last Will & Testament	LWT messages, Configuration, Use cases		✅	✅	✅
Retained Messages	Definition, Use cases, Pros & Cons		✅	✅	✅
Advanced Features	MQTT over WebSockets, Bridge, Clustering			✅	✅
Best Practices	Topic naming, QoS selection, Security, Scalability	✅	✅	✅	✅

Interview question

Basic

1. What is MQTT and why is it used?
2. Explain the publish/subscribe model in MQTT.
3. What are the key features of MQTT?
4. Which transport protocol does MQTT primarily use?
5. What are MQTT clients and brokers?
6. Explain the concept of Topics in MQTT.
7. What is QoS in MQTT?
8. List the different QoS levels in MQTT.
9. Which TCP/IP port is commonly used by MQTT?
10. What is the difference between MQTT and HTTP?
11. What is the use of the CONNECT packet in MQTT?
12. Explain the PUBLISH packet in MQTT.
13. What is the role of the SUBSCRIBE packet in MQTT?
14. What is the role of the UNSUBSCRIBE packet in MQTT?
15. What is the use of the DISCONNECT packet in MQTT?
16. What is the difference between MQTT broker and client?
17. What is retained message in MQTT?
18. What are Last Will and Testament (LWT) messages?
19. What is the difference between QoS 0, QoS 1, and QoS 2?
20. Explain MQTT session persistence.
21. What are clean sessions in MQTT?
22. Why is MQTT considered lightweight?
23. What is the default port number of MQTT over TLS/SSL?
24. What are wildcards in MQTT topics?
25. Explain the difference between single-level (+) and multi-level (#) wildcards in MQTT.

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Intermediate

1. Explain the role of persistent sessions in MQTT.
2. What is the difference between retained messages and QoS in MQTT?
3. How does MQTT handle offline clients?
4. What is the purpose of Keep Alive in MQTT?
5. How does MQTT handle message ordering?
6. Explain the DUP flag in MQTT packets.
7. What is the significance of Packet Identifier in MQTT?
8. How does MQTT handle authentication?
9. What are MQTT v3.1.1 and v5.0 differences?
10. Explain the concept of Shared Subscriptions in MQTT 5.0.
11. What is message expiry in MQTT 5.0?
12. Explain the concept of User Properties in MQTT 5.0.
13. What is Session Expiry in MQTT 5.0?
14. What is Payload Format Indicator in MQTT 5.0?
15. Explain Content Type property in MQTT 5.0.
16. What is Subscription Identifier in MQTT 5.0?
17. What are flow control mechanisms in MQTT?
18. How does MQTT ensure reliability over TCP?
19. What is MQTT-SN and how is it different from MQTT?
20. Explain MQTT over WebSockets.
21. What are common MQTT security mechanisms?
22. How can TLS be used with MQTT?
23. How does MQTT perform load balancing?
24. What is the difference between MQTT and AMQP?
25. What are some popular MQTT broker implementations?

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Advanced

1. How does clustering work in MQTT brokers?
2. What are the scaling challenges in MQTT?
3. How does MQTT ensure high availability?
4. Explain how retained messages can be misused.
5. How do you implement access control in MQTT?
6. What are topic aliasing features in MQTT 5.0?
7. Explain MQTT bridge connections.
8. How does MQTT handle large payloads?
9. What are some strategies to secure IoT devices using MQTT?
10. How does MQTT handle backpressure?
11. Explain the concept of inflight messages.
12. What is the impact of QoS levels on bandwidth usage?
13. Explain MQTT message deduplication.
14. What is the role of a Session State in MQTT?
15. How does MQTT deal with duplicate messages?
16. What is the maximum QoS supported by MQTT?
17. How do MQTT brokers handle topic hierarchy?
18. Explain persistent vs non-persistent storage in MQTT brokers.
19. How do MQTT clients reconnect after failures?
20. What are best practices for MQTT topic naming?
21. Explain MQTT message ordering guarantees.
22. What are retained message pitfalls?
23. Explain MQTT message compression.
24. How does MQTT handle resource-constrained devices?
25. Explain MQTT message delivery semantics.

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Expert

1. Compare MQTT v3.1.1 and v5.0 in detail.
2. How do you scale MQTT for millions of devices?
3. How do you integrate MQTT with cloud providers like AWS IoT or Azure IoT Hub?
4. Explain how MQTT can be integrated with Kafka.
5. How do you monitor MQTT broker performance?
6. What are advanced load-balancing strategies for MQTT?
7. How can you implement multi-tenancy in MQTT?
8. Explain the role of back-end databases with MQTT brokers.
9. How do you secure MQTT at scale?
10. Explain MQTT over QUIC protocol.
11. How do you handle distributed MQTT brokers?
12. Explain MQTT message traceability.
13. How do you implement custom authentication plugins for brokers?
14. How does MQTT interact with REST APIs?
15. What are common challenges in MQTT-based IoT systems?
16. How do you optimize MQTT for high-frequency trading-like systems?
17. Explain QoS 2 message exchange flow with packet sequence.
18. What is the impact of network latency on MQTT?
19. How to benchmark an MQTT broker?
20. Explain MQTT with Edge Computing.
21. How do you debug MQTT message flow in production?
22. How do you achieve end-to-end security in MQTT IoT ecosystems?
23. How to design a fault-tolerant MQTT system?
24. Explain MQTT integration with event-driven microservices.
25. What is the future of MQTT in IoT and real-time messaging?

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