Chapter 5 - Application Services
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Questions and Answers

What HTTP verb is used to delete a skier's profile?

  • GET
  • PUT
  • POST
  • DELETE (correct)

    • What is the expected response code for a successful GET request?

  • 200 (correct)
  • 404
  • 500
  • 400

    • Which of the following statements is true regarding the HTTP PUT request?

  • It updates the complete representation of a resource. (correct)
  • It deletes a resource permanently.
  • It retrieves information about a resource.
  • It appends information to an existing resource.

    • What does the URI '/skico.com/skiers/768934' represent?

    <p>The specific resource for skier 768934.</p> Signup and view all the answers

    When making an API call to put a new city for a skier, what must the client provide?

    <p>All profile details including the new city.</p> Signup and view all the answers

    What is typically the format for payloads in HTTP requests?

    <p>JSON</p> Signup and view all the answers

    Which HTTP verb indicates the intention to retrieve a resource?

    <p>GET</p> Signup and view all the answers

    In the context of HTTP APIs, how are resources generally identified?

    <p>By their unique URIs.</p> Signup and view all the answers

    What is the primary purpose of an API in a distributed system?

    <p>To specify the types of requests and data interactions</p> Signup and view all the answers

    Which of the following features is NOT typically associated with application servers?

    <p>Data storage</p> Signup and view all the answers

    What is horizontal scaling?

    <p>Adding more servers to distribute load</p> Signup and view all the answers

    Which term describes a system design that allows services to operate independently and communicate over a network?

    <p>Microservice architecture</p> Signup and view all the answers

    What is the role of load balancing in scalable systems?

    <p>To distribute incoming requests across multiple servers</p> Signup and view all the answers

    In terms of application services, what does state management refer to?

    <p>Maintaining consistent data across requests</p> Signup and view all the answers

    What best describes distributed caching?

    <p>Using multiple caches to improve data retrieval times</p> Signup and view all the answers

    Which of the following is a benefit of asynchronous messaging in distributed systems?

    <p>Improves system performance by decoupling message senders and receivers</p> Signup and view all the answers

    What is the primary reason for utilizing a fixed-size database connection pool in servlets?

    <p>To manage the limited number of connections efficiently</p> Signup and view all the answers

    How does a servlet obtain a connection from the database connection pool?

    <p>The servlet requests a connection, which is granted if available</p> Signup and view all the answers

    What occurs when a servlet requests a connection but the connection pool is full?

    <p>The servlet is blocked until a connection becomes available or a timeout occurs</p> Signup and view all the answers

    What can cause request response time to increase in a servlet processing environment?

    <p>Significant queue delays for thread allocation and database connections</p> Signup and view all the answers

    What can happen if a server experiences high load and has limited resources?

    <p>Requests may be rejected if they exceed server capacity</p> Signup and view all the answers

    What impact does context switching have on server performance in a heavily loaded environment?

    <p>It typically degrades performance due to increased overhead</p> Signup and view all the answers

    What configuration aspects can be adjusted in an application server like Tomcat to optimize performance?

    <p>The size of the database connections and the heap size</p> Signup and view all the answers

    What resource affects the processing capacity of a Tomcat container?

    <p>The total number of vCPUs and memory allocated as heap size</p> Signup and view all the answers

    What is the main reason adding more traffic lanes might not alleviate traffic chaos?

    <p>The highway ends at a one-lane road with traffic lights.</p> Signup and view all the answers

    What role do services play in a scalable software system?

    <p>They serve as the heart and define capabilities through an API.</p> Signup and view all the answers

    What happens when all threads in an application server's thread pool are utilized?

    <p>Requests are queued until a thread becomes available.</p> Signup and view all the answers

    What is the benefit of scaling services out horizontally using a load balancer?

    <p>It enhances the application's availability by distributing requests.</p> Signup and view all the answers

    Why are stateless services recommended for scalable architectures?

    <p>They reduce complexity in handling failures and load balancing.</p> Signup and view all the answers

    What is the primary benefit of horizontal scaling?

    <p>It increases processing capacity by adding more servers.</p> Signup and view all the answers

    What is a feature of load balancers that can support stateful services?

    <p>Sticky sessions.</p> Signup and view all the answers

    Why must servers be stateless in a horizontally scaled system?

    <p>To allow any service replica to handle any request.</p> Signup and view all the answers

    What is a complexity associated with stateful services as compared to stateless services?

    <p>They are harder to scale and manage during failures.</p> Signup and view all the answers

    What happens if a load balancer routes requests to stateful services incorrectly?

    <p>Some service replicas may become overloaded.</p> Signup and view all the answers

    How does increased availability relate to having multiple replicas in a system?

    <p>Requests can be rerouted to other replicas if one fails.</p> Signup and view all the answers

    What is one drawback of relying solely on technology suppliers' documentation for load balancer knowledge?

    <p>Key information can be buried in many details.</p> Signup and view all the answers

    What is the role of the load balancer in a horizontally scaled system?

    <p>To distribute requests across services and optimize response time.</p> Signup and view all the answers

    What is a single point of failure (SPoF) and why is it undesirable?

    <p>It represents a risk where service becomes unavailable if one instance fails.</p> Signup and view all the answers

    What technology can externalize session state, making services stateless?

    <p>Spring Session and Redis.</p> Signup and view all the answers

    What is a crucial factor for a scalable system to be effective?

    <p>Availability must not be compromised at any point.</p> Signup and view all the answers

    HTTP is known as a stateless protocol, meaning each request is executed independently.

    <p>True</p> Signup and view all the answers

    Conversational state refers to information that is lost between requests.

    <p>False</p> Signup and view all the answers

    Server implementations that need to scale should store conversational state.

    <p>False</p> Signup and view all the answers

    A servlet can obtain a connection from a database connection pool multiple times without issues.

    <p>True</p> Signup and view all the answers

    If a request is poorly formatted, the server will return a 200 status code.

    <p>False</p> Signup and view all the answers

    State management in application services refers to the technique of retaining data across multiple requests.

    <p>True</p> Signup and view all the answers

    The skierID should be extracted from the request URI to handle requests correctly.

    <p>True</p> Signup and view all the answers

    HTTP requests must always contain sufficient information for the server to satisfy the request regardless of previous interactions.

    <p>True</p> Signup and view all the answers

    A stateful service retains conversational state from previous requests.

    <p>True</p> Signup and view all the answers

    A PUT request to update a skier's profile does not require the unique identifier of the resource.

    <p>False</p> Signup and view all the answers

    Stateless services do not hold any information about earlier requests.

    <p>True</p> Signup and view all the answers

    Using a stateful service can increase the amount of data passed between clients and services.

    <p>True</p> Signup and view all the answers

    In a stateful service, each request requires the client to provide all required information for processing.

    <p>False</p> Signup and view all the answers

    When a user logs in, a session state object is often created to track their interactions.

    <p>True</p> Signup and view all the answers

    Managing conversational state is less complex than handling stateless services.

    <p>False</p> Signup and view all the answers

    Stateful services are recommended primarily for applications with high traffic loads.

    <p>False</p> Signup and view all the answers

    An application server is responsible for accepting requests from clients and applying application logic to the requests.

    <p>True</p> Signup and view all the answers

    The Java Enterprise Edition (JEE) is a lightweight framework specifically designed for application servers.

    <p>False</p> Signup and view all the answers

    Stateless APIs are crucial for scalable services to retain state pertaining to client sessions.

    <p>False</p> Signup and view all the answers

    Apache Tomcat is an open-source implementation of a portion of the JEE platform.

    <p>True</p> Signup and view all the answers

    In the context of application servers, Flask is a server that supports Ruby.

    <p>False</p> Signup and view all the answers

    Horizontal scaling involves adding additional servers to handle increased traffic.

    <p>True</p> Signup and view all the answers

    Express.js is a framework used for building applications in the Java programming language.

    <p>False</p> Signup and view all the answers

    External data stores are used to retain state for services that must retain client session information.

    <p>True</p> Signup and view all the answers

    Node.js is a multiple-threaded environment that does not support asynchronous programming.

    <p>False</p> Signup and view all the answers

    Tony Bourke's book, Server Load Balancing, is a useful resource for understanding the field of load balancing.

    <p>True</p> Signup and view all the answers

    The Apache Tomcat Executor does not have any default configuration settings.

    <p>False</p> Signup and view all the answers

    Experiments by Ruijie Xiao were conducted at Northeastern University in Boston.

    <p>False</p> Signup and view all the answers

    A broad perspective on load balancing can be gained from the work of Roy T. Fielding.

    <p>True</p> Signup and view all the answers

    A load balancer will consistently send requests to a service that is unresponsive.

    <p>False</p> Signup and view all the answers

    Elasticity allows a service to dynamically reduce its capacity as request loads decrease.

    <p>True</p> Signup and view all the answers

    Health checks by the load balancer involve sending requests at random intervals.

    <p>False</p> Signup and view all the answers

    A service replica assigned a weight of 2 will receive fewer requests than a replica assigned a weight of 1.

    <p>False</p> Signup and view all the answers

    Scaling policies can only be defined using CPU metrics in a load balancer.

    <p>False</p> Signup and view all the answers

    An Auto Scaling group maintains a fixed number of service instances regardless of load changes.

    <p>False</p> Signup and view all the answers

    A transient failure in a service will lead to its permanent removal from the load balancer's target pool.

    <p>False</p> Signup and view all the answers

    Load balancers require a tight integration with application monitoring to achieve elasticity.

    <p>True</p> Signup and view all the answers

    Study Notes

    Application Services

    • Services are at the core of distributed systems, providing business logic and interacting with clients via APIs
    • APIs define an agreement between clients and services specifying request types, data, and expected results
    • Services are typically implemented using HTTP verbs acting on resources identified by URIs
    • Service design is like object-oriented or ER modeling but focused on resources exposed to clients
    • Databases often utilize connection pools to manage limited resources
    • Application server configurations, such as thread pools, database connections, and queue sizes, can be adjusted for efficient performance
    • Horizontal scaling involves distributing requests across multiple service instances
    • Stateless services are crucial for horizontal scaling and simplify failure handling
    • Load balancers distribute requests across service instances, employing various policies to optimize efficiency and response time
    • Stateful services can cause imbalances in load distribution and complicate failure recovery
    • APIs are complex and require careful design, resource modeling is key
    • JEE provides abstractions for building services
    • Load balancer information is often found in vendor documentation

    State Management

    • HTTP is a stateless protocol, meaning each request is executed independently.
    • Conversational state is information retained between requests, allowing subsequent requests to assume knowledge of previous interactions.
    • Stateful services maintain conversational state, reducing database retrieval frequency and data transfer.
    • Stateful services are attractive for services with light request loads but become problematic as load increases.

    Stateless Services

    • Stateless services do not assume any conversational state from previous calls.
    • Clients must provide all necessary information for each request to be processed individually.
    • Scalable services need stateless APIs for better performance.
    • State must be stored externally in stateless services.

    Application Servers

    • Application servers handle requests from clients, apply business logic, and return results.
    • Examples: Java Enterprise Edition (JEE), Express.js, Flask, Go's net/http package.
    • Apache Tomcat is a popular open-source implementation of a subset of JEE.

    Load Balancing

    • Load balancers distribute requests across multiple service instances to prevent overload.
    • They monitor service health and remove unresponsive instances.
    • Load balancer types include round-robin, weighted round-robin, and least connections.

    Health Monitoring

    • Load balancers perform health checks by sending pings and attempting connections to test service health.
    • Unresponsive or failed services are removed from the load balancing pool and re-added once healthy.

    Elasticity

    • Elasticity allows applications to dynamically provision new service capacity to handle increased load.
    • Scaling policies define when to scale up or down based on metrics like CPU utilization.
    • AWS Auto Scaling groups provide a mechanism for elastic load balancing.

    Horizontal Scaling

    • Scaling up by adding more resources to existing instances (vertical scaling) eventually reaches a limit.
    • Horizontal scaling adds new instances to handle increased load, improving performance and resilience.
    • Load balancing helps distribute requests evenly across multiple instances in a horizontal scaling setup.

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    Chapter 5. Application Services PDF

    Description

    This quiz explores the essential concepts of application services within distributed systems. It covers topics like API agreements, service design, performance configurations, and scaling strategies. Test your understanding of how services interact with clients and manage resources efficiently.

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