Q31-Q35

Q31: What is pods and how it is related to Docker images and Docker containers?

Q32: What is the use of Compose Docker file?

Q33. What are the advantages and disadvantages of Docker and containers?

Q34. What are the advantages and disadvantages of microservices?

Q35:  What is API Gateway?

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

Q31: What is pods and how it is related to Docker images and Docker containers?

Answer:
>> A Pod is the smallest deployable unit in Kubernetes.
>> It can contain one or more containers
>> All containers in a Pod share: Network namespace, Storage volumes, Lifecycle
>> Containers inside Pods are created from Docker images.
>> Kubernetes uses these images to deploy and manage containers at scale.

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Q32: What is the use of Compose Docker file?

Answer:

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

Q33. What are the advantages and disadvantages of Docker and containers?

Answer:

Advantages:

1. Portability (Build once, run anywhere)

Containers include everything the app needs — libraries, configs, binaries — so the same image runs identically on a developer’s laptop, a test server, or Azure Kubernetes Service (AKS).

2. Lightweight and Fast

Containers share the host OS kernel instead of running their own OS like a VM.

Startup time: seconds, not minutes.

Memory footprint: far smaller than a VM.

This makes them excellent for microservices and serverless workloads.

3. Scalability

Containers work beautifully with orchestration platforms (like Kubernetes, AKS, ECS). You can horizontally scale easily — spin up or down containers as load changes.

4. Simplifies Microservices

Each microservice can be packaged independently, with its own dependencies and runtime. No “dependency hell” or version conflicts.

Disadvantages:

1. Complexity at Scale

Running one or two containers is easy. Running hundreds across nodes? You need orchestration (Kubernetes, Docker Swarm), which adds complexity in networking, storage, and monitoring.

2. Limited Isolation (Compared to VMs)

Containers share the same OS kernel. A kernel exploit could affect all containers.

Security-sensitive apps sometimes prefer full VM isolation.

3. Persistent Storage Challenges

Containers are stateless by design. Managing persistent volumes (for databases or file storage) is trickier — you must rely on external volumes or cloud storage.

4. Learning Curve

For teams new to DevOps, Dockerfiles, image registries, and orchestration can be intimidating. Proper governance, security, and tagging policies must be defined. 

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

Q34. What are the advantages and disadvantages of microservices?

Answer:

Microservices usually have their own models and database. 

Advantages:

1. Independent Deployment – Each service can be developed, tested, and deployed separately without impacting the rest of the system. This enables faster releases and easier maintenance.

2. Scalability – You can scale only the services that need more resources (e.g., payment or search service) instead of scaling the whole application.

3. Technology Flexibility – Different microservices can use different technology stacks (.NET, Node.js, Python, etc.) based on what fits best.

4. Fault Isolation – A failure in one microservice usually doesn’t crash the entire system. Other services continue running, improving reliability.

5. Faster Development Cycles – Smaller, independent teams can work in parallel on different services, increasing productivity.

6. Better Alignment with DevOps & Cloud – Microservices fit naturally with CI/CD pipelines, containers (Docker), and orchestrators (Kubernetes), which helps in automation and continuous delivery.

Disadvantages:

1. Increased Complexity – You move from one large application to a distributed system. Managing multiple services, deployments, and dependencies is more complex.

2. Data Consistency Challenges – Each microservice typically has its own database, making transactions across services difficult. You often need patterns like Saga or eventual consistency.

3. Communication Overhead – Network calls replace local method calls, adding latency and requiring robust error handling and retry logic.

4. Difficult Testing & Debugging – End-to-end testing and debugging across multiple services can be hard, as you must trace requests through different components.

5. Higher Infrastructure Cost – Each service may require its own container, configuration, logging, and monitoring setup.

6. Steeper Learning Curve – Teams must understand distributed system design, observability, API versioning, and deployment automation.

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

Q35. What is API Gateway?

Answer:

Api Gateway is a pattern we use in microservices architecture. It is a API management tool that sits between a client and a collection of backend services. An API gateway acts as a reverse proxy to accept all application programming interface (API) calls, aggregate the various services required to fulfill them, and return the appropriate result

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

Q26-Q30

Q26. What is aggregator Design pattern?

Q27: what is the difference between orchestration and choreography in microservices architecture

Q28: 

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Q26. What is aggregator Design pattern?

Answer:

The Aggregator Design Pattern in microservices is a structural pattern used when you need to gather data from multiple microservices and present it as a unified response.

Keyconcepts:

1. The Aggregator Design Pattern usually implemented with API Gateway or BFF (Backend for Frontend) Patterns. 

2. Create a BFF or Aggregator Service using Azure Functions or Azure API App as an Aggregator Microservice. Use Azure Logic Apps (Low-code Option) as well. 

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Q27: what is the difference between orchestration and choreography in microservices architecture

Answer:

Aspect	Orchestration	Choreography
Definition	A central service (orchestrator) controls the interactions and flow between microservices.	Each microservice reacts to events and decides what to do, with no central controller.
Control Flow	Centralized — one service knows and manages the process steps.	Decentralized — each service decides its behavior based on events.
Analogy	Conductor leading an orchestra.	Dancers responding to the rhythm individually in a flash mob.
Coupling	More tightly coupled — the orchestrator needs to know all participating services.	Loosely coupled — services publish/subscribe to events without knowing each other.
Communication Pattern	Often synchronous (REST calls, workflows).	Asynchronous (event-driven: e.g., Kafka, Azure Event Grid, RabbitMQ).
Tools	Azure Durable Functions, AWS Step Functions, Netflix Conductor, Camunda.	Kafka, Azure Event Grid, NATS, RabbitMQ.
Visibility	Easier to trace and monitor (central point of control).	Harder to trace (distributed decisions and flows).

Use Orchestration When...	Use Choreography When...
Business process is complex and needs strict control.	You want highly decoupled, event-driven architecture.
You need a clear view of the flow and error handling.	Scalability and independence of services are top priority.
Easier debugging/tracking is important.	The system must evolve flexibly over time.

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Q21-Q25

Q21: Define Event Sourcing Architecture Design pattern? [Microservice Architecture Design patterns -- Database per Microservice, Event Sourcing, CQRS, Saga, BFF, API Gateway, Strangler, Circuit Breaker, Externalized Configuration, Consumer-Driven Contract Tracing]

Q22: Define Saga Architecture Design pattern? 

Q23: What is BFF ( Backend for Frontend) Architecture Design pattern?

Q24: What is API GateWay Architecture Design pattern?

Q25: Difference between Reverse proxy and Forward Proxy service/ Layer?

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Q21: Define Event Sourcing Architecture Design pattern? 

Answer:

Here in this pattern Instead of storing the current state/ Final state of an object in database, Event Sourcing persists all events that occur in the application, allowing the state of the object to be reconstructed at any point in time.

In this pattern, every state change in the application is captured as an event and stored as a log of events. The state of the application can be reconstructed by replaying these events. This means that Event Sourcing provides an audit log of all changes that occur in the application.

For example, consider an e-commerce application. When a user places an order, an OrderPlaced event is generated and stored in the log. When the order is shipped, a ShipmentMade event is generated and stored in the log.

If the order is canceled, a OrderCanceled event is generated and stored in the log. By replaying the events, the current state of the order can be determined.

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Q22: Define Saga Architecture Design pattern? 

Answer:

The Saga pattern provides a way to manage transactions that involve multiple microservices. It is used to ensure that a series of transactions across multiple services are completed successfully, and if not, to roll back or undo all changes that have been made up to that point.

Advantage of using SAGA 

1. Can be used to maintain the data consistency across multiple services without tight coupling.

The disadvantage of using SAGA

Complexity of the SAGA design pattern is high from the programmer's point of view and developers are not well accustomed to writing sagas as traditional transactions.

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Q23: What is BFF ( Backend for Frontend) Architecture Design pattern?

Answer:

Backends for Frontends (BFF) is a design pattern used in microservice architecture to handle the complexity of client-server communication in the context of multiple user interfaces. It suggests having a separate back-end service for each frontend to handle the specific needs of that interface.

This allows developers to optimize the data flow, caching, and authentication mechanisms for the unique needs of the front-end while keeping the back-end services modular and decoupled.

For example, suppose you have a web application and a mobile application that need to access the same set of services. In this case, you can create separate back-end services for each application, each optimized for the specific platform.

The web application back-end can handle large amounts of data for faster loading, while the mobile application back-end can optimize for lower latency and network usage.

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Q24: What is API GateWay Architecture Design pattern?

Answer:

The API Gateway Pattern is another common design pattern used in microservices architecture that involves an API gateway, which acts as an entry point for all incoming API requests. It provides a single point of entry for all the microservices and acts as a proxy between the clients and the microservices, routing requests to the appropriate service.

The main purpose of an API gateway is to decouple the clients from the microservices, abstracting the complexity of the system behind a simplified and consistent API. This also means that you don’t need to find and remember address of 100+ Microservice REST APIs.

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Q25: Difference between Reverse proxy and Forward Proxy service/ Layer?

Answer:

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Q16-Q20

Q16: Tell me something about CQRS? 

Q17: Do we have two different databases in CQRS?

Q18: Techniques to keep two database in Sync?

Q19: Define Database per Microservice Architecture Design pattern? [Microservice Architecture Design patterns -- Database per Microservice, Event Sourcing, CQRS, Saga, BFF, API Gateway, Strangler, Circuit Breaker, Externalized Configuration, Consumer-Driven Contract Tracing]

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Q16: Tell me something about CQRS? 

Answer:

CQRS (Command Query Responsibility Segregation) is a powerful architectural pattern often used in microservices to separate the responsibilities of reading and writing data

Benefits:

>> This separation allows each side to be optimized independently for performance, scalability, and complexity.

CQRS splits the application into two distinct parts:

Command Side (Write Model): Handles operations that change data (Create, Update, Delete).

Query Side (Read Model): Handles operations that retrieve data (Read).

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Q17: Do we have two different databases in CQRS?

Answer:

In CQRS, it's common but not mandatory to use two separate databases for the read and write sides. 

Benefits of using Two databases:

1. Independent Scaling : We can scale READ DB horizontally to handle high query loads.

2. Technology Flexibility: You might use a relational database (e.g., PostgreSQL) for writes. And a NoSQL database (e.g., MongoDB, Elasticsearch) for reads.

-----------------------------------------------------------------------------------------------------------------------------

Q18: Techniques to keep two database in Sync?

Answer:

Techniques

1. Event-Driven Synchronization (Most Common)

• How it works: After a write operation, the system emits a domain event (e.g., OrderCreated, CustomerUpdated).
• These events are published to a message broker (like Kafka, RabbitMQ, or Azure Service Bus).
• A consumer service listens to these events and updates the read database (e.g., MongoDB).
• This enables eventual consistency (With little latency). 

2. Dual Writes (Not Recommended)#

The application writes to both databases in the same transaction or sequentially.

⚠️ Cons:

Risk of inconsistency if one write fails.

Hard to manage rollback and error handling.

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Q19: Define Database per Microservice Architecture Design pattern? 

Answer:

Each Microservice has its own dedicated Database and un related microservice can NOT access db of other domain directly. 

Advantages:

1. Understanding of Project and related DB is easy as it has limited tables and data. 

2. Scaling of DB is easy as required. 

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Q11-Q15

Q11: What is Docker?

Q12: What is Docker Containerization?
Q13: What is the basic structure of Docker file. What does it do?

Q14:  What is Docker image?

Q15: What is the difference between Docker image and Docker container?

Master Stroke:

Dockerfile → builds → Docker Image → runs as → Docker Container → managed inside → Kubernetes Pod

[Docker Related Questions]

-----------------------------------------------------------------------------------------------------------------------------

Q11: What is Docker

Answer:

Docker is an open-source platform that automates the deployment, scaling, and management of applications using containers. Containers are lightweight, portable units that package an application with all its dependencies, ensuring it runs consistently across environments—whether it's your laptop, a test server, or production

-----------------------------------------------------------------------------------------------------------------------------

Q12: What is Docker Containerization?

Answer:

Containerization is the process of packaging applications and their dependencies into containers.

Unlike Virtual Machines (VMs), containers don’t need a full guest OS. They share the host’s OS kernel but run isolated processes.

This makes containers faster, lighter, and more portable compared to VMs.

-----------------------------------------------------------------------------------------------------------------------------

Q13: What is the basic structure of Docker file. What does it do?

Answer: 

A Dockerfile is a text file that contains instructions for building a Docker image. It’s like a recipe for creating containers. 

So, a Dockerfile is essentially the blueprint for creating a Docker image.

A Dockerfile is a text file that contains a series of instructions on how to build a Docker image.

FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build

WORKDIR /src

COPY . .

RUN dotnet restore "MyMicroservice/MyMicroservice.csproj"

WORKDIR "/src/MyMicroservice"

RUN dotnet build "MyMicroservice.csproj" -c Release -o /app/build

RUN dotnet publish "MyMicroservice.csproj" -c Release -o /app/publish

FROM mcr.microsoft.com/dotnet/aspnet:8.0 AS final

WORKDIR /app

COPY --from=build /app/publish .

EXPOSE 8080

ENTRYPOINT ["dotnet", "MyMicroservice.dll"]

# 1. Uses the official .NET 8 SDK image to compile and build the application. This image contains the compiler, Build tools, Restore tools. Everything needed to build and publish your application

FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build

# 2. Sets the working directory inside the container to /src.

WORKDIR /src

# 3. Copy project files and all the source code into the container. Restores NuGet packages. Prepares all dependencies needed for the build.

COPY . .

RUN dotnet restore "MyMicroservice/MyMicroservice.csproj"

# 4. Changes the working directory to the project folder. Builds the application in Release mode.

WORKDIR "/src/MyMicroservice"

RUN dotnet build "MyMicroservice.csproj" -c Release -o /app/build

# 5. Publish the app. Prepares the app for runtime by including only necessary files.

RUN dotnet publish "MyMicroservice.csproj" -c Release -o /app/publish

# 6. Use the runtime image for the final container. Uses a smaller runtime-only image. Its just a core runtime image. Not like we have in Step 1, which is much bigger. 

FROM mcr.microsoft.com/dotnet/aspnet:8.0 AS final

WORKDIR /app

COPY --from=build /app/publish .

# 7. Expose the port your service listens on

EXPOSE 8080

# 8. Set the entry point. Defines the command to run when the container starts.

ENTRYPOINT ["dotnet", "MyMicroservice.dll"]

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Q14:  What is Docker image?

Answer:

A Docker image is a snapshot of a container's file system and configuration. It’s built from a Dockerfile and contains everything needed to run an app:

Code, Runtime, Libraries, Environment variables

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Q15: What is the difference between Docker image and Docker container?

Answer:

Docker Image - 

1- Blueprint for creating containers

2. Created from Docker file. 

3. Its a static instance/snapshot of your application/code. 

Docker Containers: 

1- They are created from Image. They are running instance of an image. 

2. Created from an image. 

3. Running instance of an image. 

Points:

A single image can have multiple containers running on it. 

Image is like a class in dotnet while containers are like object of that class. 

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Q6-Q10

Q6: What could be your folder structure for MS project in C#?

Q7: What is circuit breaker design pattern? When to use.

Q8: What are the various states of Circuit breaker design pattern?

Q9: How Circuit monitors the failure and get activated. How it changes it states to normal again?

Q10: List various Microservices Architecture design pattern?

Circuit Design Pattern

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Q6: What could be your folder structure for MS project in C#?

Answer:

MyService/

│

├── MyService.Api/               # API layer (Controllers, Startup, Program)

│   ├── Controllers/

│   ├── Models/

│   ├── DTOs/

│   ├── Startup.cs

│   └── Program.cs

│

├── MyService.Application/       # Business logic layer

│   ├── Interfaces/

│   ├── Services/

│   └── DTOs/

│

├── MyService.Domain/            # Core domain logic

│   ├── Entities/

│   ├── ValueObjects/

│   ├── Exceptions/

│   └── Interfaces/

│

├── MyService.Infrastructure/    # Data access, external integrations

│   ├── Persistence/             # EF Core DbContext, Repositories

│   ├── Migrations/

│   └── ExternalServices/

│

├── MyService.Tests/              # Unit and integration tests

│

└── dockerfile                    # For containerization

Key points for microservices:

API layer → Handles HTTP endpoints (Controllers, minimal APIs).

Application layer → Contains business logic, services, and use cases.

Domain layer → Pure business models and rules, independent of frameworks.

Infrastructure layer → Database, external APIs, message queues.

Tests → Unit tests for each layer, integration tests for endpoints.

-----------------------------------------------------------------------------------------------------------------------------

Q7: What is circuit breaker design pattern? When to use. 

Answer:

It acts like an electrical circuit breaker: it monitors for failures and stops the flow of requests to a failing service to prevent cascading failures and allow time for recovery.

When to Use:

• When calling remote services, APIs, or databases that might fail or become unresponsive.
• In microservices where one service depends on another.
• When you want to fail fast instead of waiting for timeouts.

In this pattern, a circuit breaker acts as a safety net between the client and the service, protecting the client from failures in the service. The circuit breaker monitors the status of the service and, if it detects that the service is failing, it can open the circuit and prevent further requests from being sent to the service until the service has recovered.

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Q8: What are the various states of Circuit breaker design pattern. How Circuit monitors the failure and get activated. How it changes it states to normal again?

Answer:

Different states in the circuit break pattern

Closed - When everything works well according to the normal way, the circuit breaker remains in this closed state.

Open -  When the number of failures in the system exceeds the maximum threshold, this will lead to open up the open state. This will give the error for calls without executing the function.

Open -Half (Half Open Half Close) - After having run the system several times, the circuit breaker will go on to the half-open state in order to check the underlying problems are still exist. 

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Q9: How Circuit monitors the failure and get activated. How it changes it states to normal again?

Answer:

Here’s how it works in simple terms:

1. Normal Operation (Closed State)

• Requests flow normally to the downstream service.
• The Circuit Breaker monitors failures (e.g., timeouts, exceptions).
• If the failure rate crosses a configured threshold (say, 5 failures in 10 requests), it opens the circuit.

2. Failure Mode (Open State)

• No new requests are sent to the failing service — they fail fast (avoiding long waits).
• Instead, the system may: Return a fallback response Queue the request for later retry

3. Recovery Check (Half-Open State)

• After a “cool-down period” (timeout), the Circuit Breaker lets a small number of requests through to test the service.
• If they succeed → circuit goes back to Closed (normal).
• If they fail → it returns to Open for another cooldown.

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Q10: List various Microservices Architecture design pattern?

Answer:

1. Database per Microservice

2. Event Sourcing

3. CQRS

4. Saga

5. BFF (Backend for FrontEnds)

6. API Gateway

7. Strangler

8. Circuit Breaker

9. Externalized Configuration

10. Consumer-Driven Contract Tracing

11. Aggregator Design pattern. 

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