Java is a high-level, object-oriented programming language used for developing applications.

Spring Boot is a Java-based framework used to create stand-alone, production-grade Spring applications quickly.

Spring Cloud

Spring Cloud Fundamentals

1. What is Spring Cloud, and how does it enhance microservices architecture?
2. How does Spring Cloud differ from Spring Boot?
3. Explain the concept of cloud-native applications in Spring.
4. What are the major components/modules of Spring Cloud?
5. How does Spring Cloud help in achieving scalability and resiliency?
6. What is Spring Cloud Starter?
7. What is Spring Cloud Context?

Spring Cloud Config

8. What is Spring Cloud Config Server?
9. How do you externalize configuration using Spring Cloud Config?
10. Difference between native and Git-based config repositories?
11. How do you secure Spring Cloud Config endpoints?
12. How does Spring Cloud Config handle encryption and decryption?
13. What is the role of @RefreshScope?
14. How does spring.cloud.config.uri work?
15. Can Config Server work in a high-availability setup?

Spring Cloud Netflix Eureka (Service Discovery)

16. What is Eureka Server?
17. How does Eureka Client register itself?
18. Explain Eureka’s self-preservation mode.
19. What is the role of the eureka.instance.leaseRenewalIntervalInSeconds property?
20. How does Eureka handle failover?
21. What is the purpose of @EnableEurekaClient?
22. What happens when a service goes down in Eureka?
23. How does Eureka achieve service registration and heartbeat checks?

Feign Client

24. What is Spring Cloud OpenFeign?
25. How do you define a Feign client interface?
26. How does Feign handle load balancing?
27. How do you override default Feign configurations?
28. How to handle fallback in Feign?
29. How do you configure retry and timeout settings in Feign?
30. Difference between Feign and RestTemplate?
31. Can we use Feign with OAuth2?

API Gateway (Spring Cloud Gateway)

32. What is Spring Cloud Gateway?
33. How does routing work in Spring Cloud Gateway?
34. Explain the difference between Path, Host, and Method route predicates.
35. What are filters in Spring Cloud Gateway?
36. How do you add custom filters in Gateway?
37. What is a global filter vs route-specific filter?
38. How can you implement rate limiting?
39. How to configure CORS in Spring Cloud Gateway?
40. How does Spring Cloud Gateway differ from Zuul?

Circuit Breaker / Resilience4j

41. What is Circuit Breaker pattern?
42. How does Resilience4j integrate with Spring Cloud?
43. Explain the various modules of Resilience4j.
44. How do you define fallback methods in Resilience4j?
45. What is the difference between Circuit Breaker and Retry?
46. What are Bulkhead and Rate Limiter patterns?
47. How to monitor Circuit Breaker metrics?
48. How does @CircuitBreaker annotation work?
49. How do you configure timeouts in Resilience4j?

Spring Cloud Sleuth and Zipkin

50. What is distributed tracing?
51. How does Spring Cloud Sleuth work?
52. How do you propagate trace ID and span ID?
53. What is Zipkin and how does it integrate with Sleuth?
54. How do you view traces in Zipkin UI?
55. How to disable Sleuth for specific services?
56. How does Sleuth work with asynchronous calls?

Spring Cloud Bus

57. What is Spring Cloud Bus?
58. How does it help with dynamic configuration refresh?
59. What is the difference between @RefreshScope and Bus Refresh?
60. Which message brokers are supported (e.g., RabbitMQ, Kafka)?
61. How to secure Spring Cloud Bus endpoints?

Spring Cloud Stream

62. What is Spring Cloud Stream?
63. How does messaging work in Stream?
64. What are binders in Spring Cloud Stream?
65. How do you configure Kafka/RabbitMQ as a binder?
66. What are input/output channels?
67. Difference between consumer groups and partitions?
68. What is dead-letter queue handling?

Spring Cloud Kubernetes

69. What is Spring Cloud Kubernetes?
70. How does it support service discovery?
71. How do ConfigMaps and Secrets work with Spring Cloud Kubernetes?
72. How is Spring Cloud Kubernetes different from Eureka?
73. How does it handle failover and load balancing?
74. How do you refresh properties dynamically from ConfigMap?

Spring Cloud Security

75. How do you secure services in Spring Cloud architecture?
76. What is OAuth2 and how to implement it in Spring Cloud Gateway?
77. How does token relay work in microservices?
78. How do you implement Role-Based Access Control (RBAC)?
79. What are the security best practices in Spring Cloud?

Spring Cloud Load Balancer

80. What is Spring Cloud LoadBalancer?
81. How is it different from Netflix Ribbon?
82. How do you configure custom load balancing strategy?
83. How to integrate LoadBalancer with Feign?
84. What is round-robin vs weighted response time?

Advanced & Real-World Scenarios

85. How to ensure config consistency across microservices?
86. How to handle versioning in Spring Cloud Config?
87. How to implement blue-green or canary deployments?
88. How to monitor Spring Cloud services?
89. How to handle large-scale service registration with Eureka?
90. How to handle dependency cycles between services?
91. How to debug configuration loading issues?
92. How to integrate Spring Cloud with Prometheus and Grafana?
93. How to handle secrets management in Spring Cloud?
94. What is the impact of thread pool configuration in Gateway?

Spring Cloud DevOps Integration

95. How do you deploy Spring Cloud services on Kubernetes?
96. How do you externalize secrets securely in cloud-native apps?
97. What is the role of Helm in Spring Cloud deployments?
98. How to enable health checks and liveness probes?
99. How to handle graceful shutdown in Spring Cloud services?
100. How do you set up CI/CD for Spring Cloud microservices?
101. How to enable and use Actuator endpoints across all services?

1. What is Spring Cloud, and how does it enhance microservices architecture?

Spring Cloud is a set of tools for building cloud-native applications, designed to make microservices easier to develop and manage. It provides solutions to common challenges in microservices architectures, such as service discovery, configuration management, circuit breakers, routing, and load balancing. It enhances microservices by providing ready-to-use, scalable, and resilient tools that help in managing distributed systems efficiently.

2. How does Spring Cloud differ from Spring Boot?

Spring Boot simplifies the setup and configuration of a Spring application by providing pre-configured templates and defaults for building stand-alone applications. Spring Cloud, on the other hand, builds on top of Spring Boot and offers solutions specifically for building cloud-native applications, such as service discovery, configuration management, and fault tolerance. In essence, Spring Boot handles application setup, while Spring Cloud handles the distributed system concerns.

3. Explain the concept of cloud-native applications in Spring.

Cloud-native applications are designed to run in a cloud environment. These applications are built with the principles of scalability, resiliency, and flexibility in mind, leveraging microservices, continuous delivery, and automated scaling. In Spring, a cloud-native application typically uses Spring Cloud for managing distributed services and Spring Boot for building individual microservices.

4. What are the major components/modules of Spring Cloud?

Some major components/modules of Spring Cloud include:

Spring Cloud Config: For external configuration management.
Spring Cloud Netflix: Includes components like Eureka (service discovery), Ribbon (client-side load balancing), and Hystrix (circuit breaker).
Spring Cloud Stream: For building event-driven microservices.
Spring Cloud Gateway: For routing and API management.
Spring Cloud Sleuth: For distributed tracing.
Spring Cloud Bus: For messaging and event-driven architecture.
Spring Cloud Kubernetes: For deploying applications on Kubernetes.
Spring Cloud Security: For securing microservices.

5. How does Spring Cloud help in achieving scalability and resiliency?

Spring Cloud enhances scalability and resiliency by providing tools that help with:

Service Discovery: Services can discover each other dynamically (e.g., using Eureka), making it easy to scale out services.
Load Balancing: Spring Cloud integrates with Ribbon and LoadBalancer to balance the load between services.
Fault Tolerance: Using tools like Resilience4j or Hystrix for implementing circuit breakers, retries, and timeouts to ensure that services fail gracefully and remain available.
Configuration Management: With Spring Cloud Config, services can externalize their configurations, making it easier to manage and scale applications across different environments.

6. What is Spring Cloud Starter?

Spring Cloud Starter is a set of pre-configured, ready-to-use Spring Boot starters that make it easy to add Spring Cloud features to a project. These starters include dependencies for various Spring Cloud modules, such as Eureka, Config, and Gateway, enabling developers to quickly add cloud-native capabilities to their applications.

7. What is Spring Cloud Context?

Spring Cloud Context is a module in Spring Cloud that allows for managing the application context in a distributed system. It provides features like context propagation across service boundaries and helps maintain consistency across distributed services.

Spring Cloud Config

8. What is Spring Cloud Config Server?

Spring Cloud Config Server is a server-side application that provides a centralized configuration management solution. It serves configuration properties to microservices from a variety of backends, such as Git or file systems. Services can retrieve their configuration dynamically from the Config Server.

9. How do you externalize configuration using Spring Cloud Config?

You can externalize configuration in Spring Cloud Config by storing your configuration in an external repository, such as Git, and using the @RefreshScope annotation to refresh the configuration at runtime. The Config Server exposes endpoints from which the microservices can fetch their configuration.

10. Difference between native and Git-based config repositories?

Native Config Repository: Refers to configurations stored locally, often in properties files or other resources on the filesystem.
Git-based Config Repository: In this approach, configurations are stored in a Git repository, making it easier to manage, version, and track changes to configurations.

11. How do you secure Spring Cloud Config endpoints?

You can secure Spring Cloud Config endpoints by configuring Spring Security in the Config Server to use authentication and authorization. You can integrate basic authentication, OAuth2, or other security mechanisms to restrict access to the configuration endpoints.

12. How does Spring Cloud Config handle encryption and decryption?

Spring Cloud Config supports the encryption and decryption of sensitive properties. You can use symmetric encryption (e.g., AES) and provide encryption keys through environment variables or vault systems. The properties are encrypted in the Git repository and decrypted on the fly when the Config Server provides them to the microservices.

13. What is the role of `@RefreshScope`?

The @RefreshScope annotation is used to mark a Spring bean as eligible for refresh when a change in configuration is detected. This is useful when externalized configuration changes and you want to refresh the bean's properties without restarting the application.

14. How does `spring.cloud.config.uri` work?

spring.cloud.config.uri is a property in the application configuration that defines the URI of the Spring Cloud Config Server. It tells the microservices where to fetch their configuration from.

15. Can Config Server work in a high-availability setup?

Yes, the Spring Cloud Config Server can be set up in a high-availability (HA) configuration by running multiple instances behind a load balancer. This ensures that if one Config Server instance goes down, the others remain available.

Spring Cloud Netflix Eureka (Service Discovery)

16. What is Eureka Server?

Eureka Server is a service registry that allows microservices to register themselves and discover other services in a distributed system. It is part of the Spring Cloud Netflix stack and is used for service discovery, where services can dynamically discover each other without hard-coded endpoints.

17. How does Eureka Client register itself?

A Eureka client registers itself with the Eureka Server by using the @EnableEurekaClient annotation in a Spring Boot application. The client sends its metadata (e.g., hostname, port, health information) to the Eureka Server, which stores this information in its registry.

18. Explain Eureka’s self-preservation mode.

Eureka’s self-preservation mode is a feature that prevents the server from removing service instances from its registry if it cannot reach them for a period of time. This is useful for handling network partition issues or temporary service unavailability, ensuring that services aren’t erroneously marked as down.

19. What is the role of the `eureka.instance.leaseRenewalIntervalInSeconds` property?

The eureka.instance.leaseRenewalIntervalInSeconds property defines how often a service should renew its registration with Eureka. It controls the interval at which the service sends a heartbeat to Eureka to maintain its active status in the registry.

20. How does Eureka handle failover?

Eureka uses a mechanism called lease expiration to handle failover. If a registered service fails to renew its lease (heartbeat) within the specified time, Eureka considers it as unavailable and removes it from the registry. Other services trying to discover it will see it as down, and load balancers will route requests to available instances.

21. What is the purpose of `@EnableEurekaClient`?

The @EnableEurekaClient annotation is used to mark a Spring Boot application as a Eureka client. This enables the application to register itself with the Eureka server and participate in service discovery.

22. What happens when a service goes down in Eureka?

When a service goes down or becomes unavailable, Eureka detects it based on the lease expiration mechanism. If the service fails to renew its lease, it will be removed from the registry, and other services will no longer be able to discover it. Clients querying Eureka for that service will be directed to other available instances.

23. How does Eureka achieve service registration and heartbeat checks?

Eureka achieves service registration through clients sending their metadata to the Eureka server, typically through HTTP requests. Heartbeat checks are achieved through periodic "lease renewals" from the clients, where they send a message to the server indicating they are still alive. If the server stops receiving these renewals, the service is considered unavailable.

Feign Client

24. What is Spring Cloud OpenFeign?

Spring Cloud OpenFeign is a declarative HTTP client that simplifies communication between microservices. It allows developers to define RESTful web service clients using interfaces annotated with @FeignClient, which reduces the need to manually write HTTP client code.

25. How do you define a Feign client interface?

A Feign client interface is defined by annotating a Java interface with @FeignClient. You define the methods corresponding to the REST endpoints you want to call. For example:


@FeignClient("service-name")
public interface ServiceClient {
    @GetMapping("/api/data")
    String getData();
}

26. How does Feign handle load balancing?

Feign integrates with Spring Cloud’s LoadBalancer (or Ribbon) to handle load balancing. When calling a service, Feign uses the LoadBalancer to choose a healthy instance of the service based on the registered instances in the service registry (like Eureka).

27. How do you override default Feign configurations?

You can override Feign’s default configurations by creating a configuration class with custom settings, such as timeouts or interceptors, and then referencing this configuration in the @FeignClient annotation.


@FeignClient(name = "service-name", configuration = FeignConfig.class)
public interface ServiceClient {
    // methods
}

28. How to handle fallback in Feign?

Feign supports fallback using the @FeignClient annotation with the fallback attribute. You can define a fallback class that implements the Feign client interface to handle failure scenarios.


@FeignClient(name = "service-name", fallback = ServiceClientFallback.class)
public interface ServiceClient {
    // methods
}

29. How do you configure retry and timeout settings in Feign?

You can configure retries and timeouts by modifying the Feign configuration. For example, you can configure the @Configuration class to define retry behavior or customize timeouts via Feign.Builder settings.


@Bean
public Retryer feignRetryer() {
    return new Retryer.Default(1000, 5000, 3); // retries, max period, max attempts
}

30. Difference between Feign and RestTemplate?

Feign is a declarative HTTP client, meaning you define interfaces, and Spring automatically implements them. RestTemplate, on the other hand, is an imperative HTTP client, where you explicitly write the HTTP calls. Feign offers a more concise and readable approach to communication in microservices.

31. Can we use Feign with OAuth2?

Yes, Feign can be used with OAuth2 by configuring an OAuth2 token relay using Spring Cloud Security. The token is passed along with each Feign request, enabling authentication and authorization for the microservices.

API Gateway (Spring Cloud Gateway)

32. What is Spring Cloud Gateway?

Spring Cloud Gateway is a modern, lightweight API gateway built on top of Spring Framework. It provides routing, load balancing, and API management features such as security, rate limiting, and more, all in a reactive manner.

33. How does routing work in Spring Cloud Gateway?

Routing in Spring Cloud Gateway is configured using RouteLocator or application.yml files. Routes define a URI path and specify the destination, along with any filters or predicates to apply. For example:


spring:
  cloud:
    gateway:
      routes:
        - id: route1
          uri: http://localhost:8081
          predicates:
            - Path=/api/**

34. Explain the difference between Path, Host, and Method route predicates.

Path: Routes based on the URL path (e.g., /api/**).
Host: Routes based on the host header (e.g., example.com).
Method: Routes based on the HTTP method (e.g., GET, POST).

35. What are filters in Spring Cloud Gateway?

Filters are used to modify requests and responses in the gateway. They can be used for tasks like logging, authentication, rate limiting, and modifying headers. Filters can be global or route-specific.

36. How do you add custom filters in Gateway?

You can add custom filters by implementing the GatewayFilter interface and registering them with a RouteLocator or using the @Bean definition in a configuration class.

37. What is a global filter vs route-specific filter?

Global Filter: Applies to all routes in the gateway.
Route-Specific Filter: Applies only to specific routes defined in the configuration.

38. How can you implement rate limiting?

You can implement rate limiting using Spring Cloud Gateway’s RateLimiter filter. It can limit the number of requests per user, IP address, or other criteria.


spring:
  cloud:
    gateway:
      filters:
        - name: RequestRateLimiter
          args:
            keyResolver: remoteAddress
            limit: 10
            duration: 60

39. How to configure CORS in Spring Cloud Gateway?

You can configure CORS (Cross-Origin Resource Sharing) by setting the appropriate CORS filter in the gateway’s configuration.


spring:
  cloud:
    gateway:
      globalfilters:
        - name: CORS
          args:
            allowedOrigins: "*"
            allowedMethods: "GET, POST, PUT"

40. How does Spring Cloud Gateway differ from Zuul?

Spring Cloud Gateway is a more modern, reactive-based API gateway, whereas Zuul is based on a blocking, servlet-based model. Gateway offers more features, is non-blocking, and is built to take advantage of Spring WebFlux.

Circuit Breaker / Resilience4j

41. What is Circuit Breaker pattern?

The Circuit Breaker pattern is a design pattern used to detect failures in a system and prevent those failures from cascading to other parts of the system. It wraps service calls in a “circuit,” which can be "closed" (normal operation), "open" (failure state), or "half-open" (testing recovery state). If a certain threshold of failures is exceeded, the circuit breaker “opens,” and further attempts to call the service are rejected, allowing time for recovery.

42. How does Resilience4j integrate with Spring Cloud?

Resilience4j is a lightweight, non-blocking fault tolerance library that integrates with Spring Cloud to provide features like circuit breaking, retries, rate limiting, and bulkheading. It can be easily configured in Spring Boot applications using annotations like @CircuitBreaker and @Retry, or via properties in the application.yml.

43. Explain the various modules of Resilience4j.

Resilience4j offers several modules:

CircuitBreaker: Prevents system failure by switching off calls to failing services.
Retry: Automatically retries failed operations based on custom rules.
RateLimiter: Limits the rate of requests to a service.
Bulkhead: Limits the number of concurrent calls to a service, isolating failures.
TimeLimiter: Restricts the maximum time for a request to complete.

44. How do you define fallback methods in Resilience4j?

Fallback methods in Resilience4j are defined by creating a method that is called when the main method fails. You can use the @CircuitBreaker annotation and specify a fallback method:


@CircuitBreaker(name = "serviceName", fallbackMethod = "fallbackMethod")
public String callService() {
    // Service call logic
}

public String fallbackMethod(Exception ex) {
    return "Fallback response";
}

45. What is the difference between Circuit Breaker and Retry?

Circuit Breaker: Prevents further calls to a failing service to avoid cascading failures, and allows the system to recover.
Retry: Automatically retries failed operations, typically with exponential backoff, before giving up or triggering a fallback.

46. What are Bulkhead and Rate Limiter patterns?

Bulkhead: Isolates different parts of a system by limiting the number of concurrent calls to a particular service, reducing the risk of failure propagation.
Rate Limiter: Limits the number of requests to a service within a specific time frame, preventing overloading.

47. How to monitor Circuit Breaker metrics?

Resilience4j provides integration with metrics libraries like Micrometer to monitor circuit breaker status, metrics like success and failure counts, and the open/closed state of the circuit breaker.


CircuitBreakerRegistry registry = CircuitBreakerRegistry.ofDefaults();
CircuitBreaker circuitBreaker = registry.circuitBreaker("serviceName");
Metrics.ofCircuitBreaker(circuitBreaker);

48. How does `@CircuitBreaker` annotation work?

The @CircuitBreaker annotation is used to wrap a method with a circuit breaker. It allows you to specify the behavior when a method fails (i.e., fallback). The circuit breaker monitors the method execution and transitions between closed, open, and half-open states based on the number of failures.

49. How do you configure timeouts in Resilience4j?

Timeouts in Resilience4j can be configured for both retries and circuit breakers using properties in the application.yml file or through Java configuration. You can specify the timeout value when defining a circuit breaker or retry policy.


resilience4j.circuitbreaker:
  instances:
    serviceName:
      timeoutDuration: 500ms

Spring Cloud Sleuth and Zipkin

50. What is distributed tracing?

Distributed tracing is a method used to trace the flow of a request as it travels across multiple services in a microservices architecture. It helps to visualize the request's journey, diagnose performance bottlenecks, and understand dependencies between services.

51. How does Spring Cloud Sleuth work?

Spring Cloud Sleuth adds trace IDs and span IDs to log entries in a distributed system. It automatically propagates these IDs across service calls, enabling you to correlate logs and trace requests as they move between services.

52. How do you propagate trace ID and span ID?

Spring Cloud Sleuth automatically propagates trace IDs and span IDs by injecting them into the headers of HTTP requests or messages. When a service receives a request, it extracts the trace ID and span ID from the headers and continues the trace.

53. What is Zipkin and how does it integrate with Sleuth?

Zipkin is a distributed tracing system that collects and visualizes trace data. It integrates with Spring Cloud Sleuth to store trace information and display it in a user-friendly UI, helping to analyze request paths and performance bottlenecks.

54. How do you view traces in Zipkin UI?

Once Spring Cloud Sleuth is integrated with Zipkin, traces can be viewed in the Zipkin UI. It displays information about trace spans, showing how requests flow through different services and where delays or issues occur.

55. How to disable Sleuth for specific services?

You can disable Sleuth for specific services by configuring the spring.sleuth.enabled property in the application.yml or application.properties file:


spring.sleuth.enabled: false

56. How does Sleuth work with asynchronous calls?

Sleuth automatically injects trace context (trace ID and span ID) into the headers of asynchronous calls, ensuring that the trace context is maintained across multiple threads or services during an asynchronous process.

Spring Cloud Bus

57. What is Spring Cloud Bus?

Spring Cloud Bus is a lightweight, distributed messaging system that allows you to propagate changes (e.g., configuration changes) across microservices. It uses a message broker like RabbitMQ or Kafka to broadcast events.

58. How does it help with dynamic configuration refresh?

Spring Cloud Bus can broadcast configuration changes to all connected services. When a configuration change occurs, the Bus sends a message to refresh the configuration on all microservices that are listening for changes, avoiding the need for service restarts.

59. What is the difference between `@RefreshScope` and Bus Refresh?

@RefreshScope: Refreshes beans marked with this annotation when a configuration change occurs.
Bus Refresh: Uses the Spring Cloud Bus to broadcast a message to all services, instructing them to refresh their configuration. It works in conjunction with @RefreshScope to trigger dynamic refresh.

60. Which message brokers are supported (e.g., RabbitMQ, Kafka)?

Spring Cloud Bus supports message brokers like RabbitMQ, Kafka, and Redis to propagate events across microservices.

61. How to secure Spring Cloud Bus endpoints?

You can secure Spring Cloud Bus endpoints by using Spring Security to authenticate and authorize access to the Bus endpoints, ensuring only authorized clients can send or receive messages.

Spring Cloud Stream

62. What is Spring Cloud Stream?

Spring Cloud Stream is a framework for building event-driven microservices. It abstracts the underlying messaging middleware (e.g., RabbitMQ, Kafka) and provides a programming model to handle message-driven communication in Spring applications.

63. How does messaging work in Stream?

Messaging in Spring Cloud Stream works using binders (adapters to different message brokers) and channels. Producers send messages to an output channel, and consumers receive messages from an input channel.

64. What are binders in Spring Cloud Stream?

Binders are abstractions over message brokers like Kafka or RabbitMQ. They allow Spring Cloud Stream to interact with various messaging systems without needing to change application code.

65. How do you configure Kafka/RabbitMQ as a binder?

To configure Kafka or RabbitMQ as a binder, you need to include the appropriate dependencies and define the binder settings in the application.yml or application.properties file.


spring:
  cloud:
    stream:
      bindings:
        input:
          destination: input-topic
        output:
          destination: output-topic
      kafka:
        binder:
          brokers: localhost:9092

66. What are input/output channels?

Input Channels: Channels through which messages are consumed (e.g., @Input annotation).
Output Channels: Channels through which messages are sent (e.g., @Output annotation).

67. Difference between consumer groups and partitions?

Consumer Groups: A set of consumers that divide the load of processing messages from a topic. Each message is consumed by only one member of the group.
Partitions: Kafka topics are divided into partitions, and each partition can be consumed independently. Consumer groups can read from different partitions in parallel.

68. What is dead-letter queue handling?

A dead-letter queue (DLQ) is a message queue that stores messages that cannot be processed (e.g., due to errors or timeouts). Spring Cloud Stream supports DLQs to ensure failed messages are not lost and can be processed later.

Spring Cloud Kubernetes

69. What is Spring Cloud Kubernetes?

Spring Cloud Kubernetes provides integration between Spring applications and Kubernetes, enabling features like service discovery, configuration management, and automated scaling in Kubernetes environments. It helps Spring applications to run natively on Kubernetes while leveraging the platform's features.

70. How does it support service discovery?

Spring Cloud Kubernetes supports service discovery by integrating with Kubernetes' built-in DNS and the Kubernetes API to automatically discover services. This is similar to how service discovery works with Eureka or Consul, but uses Kubernetes native methods.

71. How do ConfigMaps and Secrets work with Spring Cloud Kubernetes?

ConfigMaps and Secrets are Kubernetes resources used to store configuration data and sensitive information, respectively. Spring Cloud Kubernetes integrates with these resources to externalize application configuration and provide secure access to sensitive data (like passwords, certificates) directly from Kubernetes.

ConfigMaps: Store non-sensitive configuration data that can be injected into the Spring application as environment variables or files.
Secrets: Store sensitive data securely, and Spring Cloud Kubernetes can use them in a similar way, ensuring secure access to the application.

72. How is Spring Cloud Kubernetes different from Eureka?

Spring Cloud Kubernetes provides native integration with Kubernetes for service discovery and configuration management, eliminating the need for additional tools like Eureka. It leverages Kubernetes DNS and API for service discovery, while Eureka provides its own registry service for service instances.

73. How does it handle failover and load balancing?

Spring Cloud Kubernetes uses Kubernetes' built-in service discovery, load balancing, and failover mechanisms. Kubernetes ensures that the pods of a service are load balanced across nodes, and if one pod fails, Kubernetes automatically reschedules it. Spring Cloud Kubernetes simply leverages these capabilities for service discovery.

74. How do you refresh properties dynamically from ConfigMap?

You can dynamically refresh properties in Spring Cloud Kubernetes by using the @RefreshScope annotation and configuring Spring to listen for changes in ConfigMap. When the ConfigMap changes, the application automatically refreshes the beans that are dependent on it.


spring:
  cloud:
    kubernetes:
      config:
        name: my-configmap

Spring Cloud Security

75. How do you secure services in Spring Cloud architecture?

Services in Spring Cloud architecture can be secured using OAuth2, JWT, basic authentication, and other security protocols. Spring Security can be integrated with Spring Cloud Gateway or individual microservices to ensure that only authenticated and authorized requests are allowed to pass through the system.

76. What is OAuth2 and how to implement it in Spring Cloud Gateway?

OAuth2 is an authorization framework that allows third-party services to access resources without sharing credentials. It can be implemented in Spring Cloud Gateway by using the spring-cloud-starter-oauth2 dependency. You can configure Gateway to act as an OAuth2 authorization server or to forward requests to an OAuth2 authorization server for authentication.


spring:
  cloud:
    gateway:
      routes:
        - id: oauth2_route
          uri: http://localhost:8081
          predicates:
            - Path=/api/**
          filters:
            - name: OAuth2AuthorizationCode

77. How does token relay work in microservices?

Token relay allows an OAuth2 token to be passed between microservices when a request is forwarded. This ensures that each service in the chain can validate the token and authorize the request based on the user's identity.

In Spring Cloud, token relay is supported by using OAuth2RestTemplate or Feign with OAuth2 integration, so that each microservice forwarding a request passes the OAuth2 token in the header.

78. How do you implement Role-Based Access Control (RBAC)?

Role-Based Access Control (RBAC) can be implemented in Spring Cloud by configuring Spring Security with roles and permissions. Each service can define the required roles for different endpoints, and these roles are checked during authorization. For example:


@PreAuthorize("hasRole('ADMIN')")
public String getAdminData() {
    return "Admin data";
}

79. What are the security best practices in Spring Cloud?

Some security best practices in Spring Cloud include:

Use OAuth2 and JWT for securing APIs.
Secure communication with HTTPS for all service interactions.
Implement role-based access control (RBAC) for microservices.
Use Spring Security to configure fine-grained access control.
Ensure proper authentication and authorization for every service call.
Regularly rotate API keys and secrets.

Spring Cloud Load Balancer

80. What is Spring Cloud LoadBalancer?

Spring Cloud LoadBalancer is a library for client-side load balancing in Spring Cloud applications. It provides an abstraction over various load balancing algorithms, such as round-robin or random selection, to distribute requests among multiple instances of a service.

81. How is it different from Netflix Ribbon?

Spring Cloud LoadBalancer is a simpler, Spring-native replacement for Netflix Ribbon. It is designed to work seamlessly with Spring Boot applications and uses Spring's native capabilities for load balancing. Ribbon, on the other hand, is a more complex library that offers additional features but is now in maintenance mode, with Spring Cloud LoadBalancer being the preferred choice.

82. How do you configure custom load balancing strategy?

You can configure a custom load balancing strategy by defining a LoadBalancer bean and specifying the strategy in your Spring Cloud configuration. For example, you can configure the round-robin strategy or any other strategy based on your requirements.


@Bean
public LoadBalancerClient loadBalancerClient() {
    return new RoundRobinLoadBalancer();
}

83. How to integrate LoadBalancer with Feign?

You can integrate Spring Cloud LoadBalancer with Feign by enabling load balancing support for Feign clients. Simply add the @EnableFeignClients annotation and configure @FeignClient to work with Spring Cloud LoadBalancer.


@FeignClient(name = "service-name")
public interface ServiceClient {
    @GetMapping("/api/data")
    String getData();
}

84. What is round-robin vs weighted response time?

Round-robin: A simple load balancing strategy that sends requests to each instance of a service in a rotating manner, ensuring an even distribution of load.
Weighted response time: A strategy that assigns more requests to instances with better response times or higher capacity, optimizing performance.

Advanced & Real-World Scenarios

85. How to ensure config consistency across microservices?

You can ensure configuration consistency across microservices using Spring Cloud Config. By storing configuration in a centralized repository (e.g., Git), all microservices can access the same configuration version, ensuring consistency across the system.

86. How to handle versioning in Spring Cloud Config?

Spring Cloud Config supports versioning by allowing you to store multiple configuration versions in a Git repository. You can configure Spring Cloud Config Server to fetch a specific version of configuration files, ensuring backward compatibility across microservices.

87. How to implement blue-green or canary deployments?

Blue-green and canary deployments can be managed using Spring Cloud and Kubernetes. By configuring deployment strategies in Kubernetes or using API Gateways, you can gradually shift traffic from the old version to the new one, ensuring minimal downtime and easy rollback if needed.

88. How to monitor Spring Cloud services?

You can monitor Spring Cloud services using tools like Spring Boot Actuator, Prometheus, Grafana, and Micrometer. These tools provide metrics, health checks, and dashboards to monitor the health and performance of microservices.

89. How to handle large-scale service registration with Eureka?

To handle large-scale service registration with Eureka, you can configure Eureka for high availability (HA) by using multiple Eureka servers, clustering, and data replication. This ensures that service registration remains reliable even under heavy load.

90. How to handle dependency cycles between services?

Dependency cycles between services can be resolved by refactoring the architecture to break circular dependencies. One common approach is to use event-driven architectures or asynchronous messaging to decouple services.

91. How to debug configuration loading issues?

You can debug configuration loading issues by enabling debug logging in Spring Cloud Config and reviewing logs. You can also use Spring Boot Actuator's /actuator/env endpoint to view the current application environment and configuration properties.

92. How to integrate Spring Cloud with Prometheus and Grafana?

You can integrate Spring Cloud with Prometheus and Grafana by using Micrometer to expose application metrics and then configure Prometheus to scrape these metrics. Grafana can then be used to visualize and create dashboards for monitoring.

93. How to handle secrets management in Spring Cloud?

Secrets management in Spring Cloud can be handled by using tools like Spring Cloud Vault, which integrates with HashiCorp Vault for secure storage and management of secrets. You can also use Spring Cloud Kubernetes to access secrets stored in Kubernetes' native secret management system.

94. What is the impact of thread pool configuration in Gateway?

Thread pool configuration in Spring Cloud Gateway impacts the gateway’s performance, as it determines how many requests the gateway can process concurrently. Proper configuration ensures that the gateway can handle high traffic efficiently without overloading the system.

Spring Cloud DevOps Integration

95. How do you deploy Spring Cloud services on Kubernetes?

You can deploy Spring Cloud services on Kubernetes by packaging them into Docker containers and deploying them as Kubernetes pods. You can use Kubernetes deployment configurations, services, and ingress controllers to manage the lifecycle of microservices.

96. How do you externalize secrets securely in cloud-native apps?

Secrets can be securely externalized in cloud-native apps using Spring Cloud Vault, Kubernetes Secrets, or AWS Secrets Manager. These tools ensure that sensitive information is stored securely and accessed only by authorized services.

97. What is the role of Helm in Spring Cloud deployments?

Helm is a package manager for Kubernetes that simplifies the deployment and management of Kubernetes applications. It allows you to package, configure, and deploy Spring Cloud applications in Kubernetes using Helm charts.

98. How to enable health checks and liveness probes?

In Kubernetes, you can configure health checks and liveness probes in the Spring Cloud services' Kubernetes deployment YAML files. This allows Kubernetes to monitor the health of the microservices and automatically restart them if needed.

99. How to handle graceful shutdown in Spring Cloud services?

You can configure graceful shutdown in Spring Cloud services by enabling the server.shutdown.grace-period property in your application configuration. This ensures that the service waits for in-flight requests to complete before shutting down.

100. How do you set up CI/CD for Spring Cloud microservices?

CI/CD for Spring Cloud microservices can be set up using tools like Jenkins, GitLab CI, or GitHub Actions. These tools help automate the build, test, and deployment processes, ensuring smooth and efficient delivery of microservices.

101. How to enable and use Actuator endpoints across all services?

You can enable and use Spring Boot Actuator endpoints by adding the spring-boot-starter-actuator dependency and exposing the necessary endpoints (e.g., health, metrics) in your application properties.


management:
  endpoints:
    web:
      exposure:
        include: health, metrics

add

Spring Cloud

Spring Cloud Fundamentals

Spring Cloud Config

Spring Cloud Netflix Eureka (Service Discovery)

Feign Client

API Gateway (Spring Cloud Gateway)

Circuit Breaker / Resilience4j

Spring Cloud Sleuth and Zipkin

Spring Cloud Bus

Spring Cloud Stream

Spring Cloud Kubernetes

Spring Cloud Security

Spring Cloud Load Balancer

Advanced & Real-World Scenarios

Spring Cloud DevOps Integration

1. What is Spring Cloud, and how does it enhance microservices architecture?

2. How does Spring Cloud differ from Spring Boot?

3. Explain the concept of cloud-native applications in Spring.

4. What are the major components/modules of Spring Cloud?

5. How does Spring Cloud help in achieving scalability and resiliency?

6. What is Spring Cloud Starter?

7. What is Spring Cloud Context?

Spring Cloud Config

8. What is Spring Cloud Config Server?

9. How do you externalize configuration using Spring Cloud Config?

10. Difference between native and Git-based config repositories?

11. How do you secure Spring Cloud Config endpoints?

12. How does Spring Cloud Config handle encryption and decryption?

13. What is the role of @RefreshScope?

14. How does spring.cloud.config.uri work?

15. Can Config Server work in a high-availability setup?

Spring Cloud Netflix Eureka (Service Discovery)

16. What is Eureka Server?

17. How does Eureka Client register itself?

18. Explain Eureka’s self-preservation mode.

19. What is the role of the eureka.instance.leaseRenewalIntervalInSeconds property?

20. How does Eureka handle failover?

21. What is the purpose of @EnableEurekaClient?

22. What happens when a service goes down in Eureka?

23. How does Eureka achieve service registration and heartbeat checks?

Feign Client

24. What is Spring Cloud OpenFeign?

25. How do you define a Feign client interface?

26. How does Feign handle load balancing?

27. How do you override default Feign configurations?

28. How to handle fallback in Feign?

29. How do you configure retry and timeout settings in Feign?

30. Difference between Feign and RestTemplate?

31. Can we use Feign with OAuth2?

API Gateway (Spring Cloud Gateway)

32. What is Spring Cloud Gateway?

33. How does routing work in Spring Cloud Gateway?

34. Explain the difference between Path, Host, and Method route predicates.

35. What are filters in Spring Cloud Gateway?

36. How do you add custom filters in Gateway?

37. What is a global filter vs route-specific filter?

38. How can you implement rate limiting?

39. How to configure CORS in Spring Cloud Gateway?

40. How does Spring Cloud Gateway differ from Zuul?

Circuit Breaker / Resilience4j

41. What is Circuit Breaker pattern?

42. How does Resilience4j integrate with Spring Cloud?

43. Explain the various modules of Resilience4j.

44. How do you define fallback methods in Resilience4j?

45. What is the difference between Circuit Breaker and Retry?

46. What are Bulkhead and Rate Limiter patterns?

47. How to monitor Circuit Breaker metrics?

48. How does @CircuitBreaker annotation work?

49. How do you configure timeouts in Resilience4j?

Spring Cloud Sleuth and Zipkin

50. What is distributed tracing?

51. How does Spring Cloud Sleuth work?

52. How do you propagate trace ID and span ID?

53. What is Zipkin and how does it integrate with Sleuth?

54. How do you view traces in Zipkin UI?

55. How to disable Sleuth for specific services?

56. How does Sleuth work with asynchronous calls?

Spring Cloud Bus

57. What is Spring Cloud Bus?

13. What is the role of `@RefreshScope`?

14. How does `spring.cloud.config.uri` work?

19. What is the role of the `eureka.instance.leaseRenewalIntervalInSeconds` property?

21. What is the purpose of `@EnableEurekaClient`?

48. How does `@CircuitBreaker` annotation work?

59. What is the difference between `@RefreshScope` and Bus Refresh?