Scalable Systems - Chapter 5: Application Services
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Questions and Answers

What does the HTTP DELETE method do when called on a skier's profile URI?

  • It retrieves the skier's current profile.
  • It updates the skier's profile information.
  • It creates a new skier's profile.
  • It deletes the skier's profile. (correct)
  • Which HTTP verb would be used to update a skier's city in their profile?

  • POST
  • PUT (correct)
  • GET
  • PATCH
  • What is the expected response format for an HTTP GET request to a skier's profile?

  • JSON (correct)
  • HTML
  • CSV
  • XML
  • What does a successful HTTP GET request return in terms of response code?

    <p>HTTP 200</p> Signup and view all the answers

    Which of the following statements about resource identification in HTTP APIs is true?

    <p>Resources are identified by unique identifiers within the API.</p> Signup and view all the answers

    When sending a PUT request, what is expected in the request body?

    <p>The complete representation of the resource.</p> Signup and view all the answers

    What type of HTTP request would provide the full profile information for a skier?

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

    In the context of HTTP APIs, how are resources conceptualized?

    <p>As objects in object-oriented design.</p> Signup and view all the answers

    What is the primary role of a servlet container in Tomcat?

    <p>To manage the life cycle of application-defined servlets</p> Signup and view all the answers

    At which default port does Tomcat listen for HTTP requests?

    <p>8080</p> Signup and view all the answers

    What happens to incoming requests when the frequency exceeds the processing capacity of the TCP listener?

    <p>Requests are queued in the Sockets Backlog</p> Signup and view all the answers

    What is the default minimum size of the thread pool in Tomcat?

    <p>25 threads</p> Signup and view all the answers

    How long does a thread remain idle before being killed to free resources in the Java virtual machine?

    <p>60 seconds</p> Signup and view all the answers

    What is the default maximum size of the thread pool in Tomcat?

    <p>200 threads</p> Signup and view all the answers

    When there are no available threads to handle a request, where are those requests maintained?

    <p>In a queue of runnable tasks</p> Signup and view all the answers

    Which of the following correctly describes the handling of HTTP requests in Tomcat?

    <p>Each request is processed in its own thread</p> Signup and view all the answers

    What type of request is used to retrieve a skier's profile?

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

    Which attribute must be known to update the skier's resource using a PUT request?

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

    What characterizes a stateful service?

    <p>It maintains knowledge from previous requests.</p> Signup and view all the answers

    Which design aspect makes stateful services appealing for light request loads?

    <p>They minimize database retrieval operations.</p> Signup and view all the answers

    What is a potential drawback of stateful services as load increases?

    <p>Difficulty in maintaining state consistency.</p> Signup and view all the answers

    What is required from the client in a stateless service?

    <p>All necessary information for processing requests.</p> Signup and view all the answers

    Which of the following are true about HTTP requests in a stateful service context?

    <p>The first request creates a session state object.</p> Signup and view all the answers

    How do JEE servlets manage session state for services?

    <p>Via the HttpSession object.</p> Signup and view all the answers

    What is the primary benefit of clients not contacting target services directly?

    <p>It enhances security by keeping services behind a perimeter.</p> Signup and view all the answers

    How does a network-level load balancer make routing decisions?

    <p>Using client IP addresses.</p> Signup and view all the answers

    What technique do load balancers use to modify packet addresses?

    <p>Network Address Translation (NAT).</p> Signup and view all the answers

    Which layer does a layer 7 load balancer operate at in the OSI model?

    <p>Application layer.</p> Signup and view all the answers

    What is a characteristic of network-level load balancers?

    <p>They operate on individual TCP or UDP packets.</p> Signup and view all the answers

    What aspect makes application-level load balancers generally slower than network-level load balancers?

    <p>They perform complex message reassembly and routing.</p> Signup and view all the answers

    Which of the following is NOT a function of a network-level load balancer?

    <p>Making decisions based on HTTP message content.</p> Signup and view all the answers

    What is a reverse proxy feature offered by application-level load balancers?

    <p>Routing requests based on query strings.</p> Signup and view all the answers

    Why might adding more traffic lanes to a highway not alleviate congestion?

    <p>Because traffic flow is hindered by subsequent bottlenecks.</p> Signup and view all the answers

    What is the main advantage of using a network load balancer over an application load balancer in terms of performance?

    <p>Higher performance under lower loads</p> Signup and view all the answers

    What is the primary function of services in a scalable software system?

    <p>To define a contract through an API for clients.</p> Signup and view all the answers

    What does a load balancer do in the context of scalable services?

    <p>It manages the pool of service instances and directs requests accordingly.</p> Signup and view all the answers

    What happens when 256 clients request services from the 4 replicas?

    <p>Both load balancers show diminished performance due to a bottleneck</p> Signup and view all the answers

    What is a significant advantage of stateless services over stateful services?

    <p>They simplify failure handling.</p> Signup and view all the answers

    How can system capacity be increased when faced with a bottleneck in load balancing?

    <p>By adding more replicas to the load balancing group</p> Signup and view all the answers

    Which of the following is NOT mentioned as a load distribution policy in load balancers?

    <p>Random allocation</p> Signup and view all the answers

    What might occur if all threads in the application server's thread pool are utilized?

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

    Why are stateful services not recommended for highly scalable systems?

    <p>They complicate load balancing and failure management.</p> Signup and view all the answers

    What is typically allocated to standard service instances in a load balancing pool to regulate distribution?

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

    What is one challenge of API design mentioned?

    <p>It presents complexity and debate.</p> Signup and view all the answers

    What performance characteristic holds true for both application and network load balancers when client load exceeds the system capacity?

    <p>Both systems experience a similar decline in performance</p> Signup and view all the answers

    What metric was used to compare the performance of the network and application load balancers?

    <p>Throughput levels</p> Signup and view all the answers

    What feature in load balancers allows them to work with stateful services?

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

    Which load balancing feature involves the assignment of a numerical value to service instances?

    <p>Weight allocation</p> Signup and view all the answers

    Study Notes

    Part II: Scalable Systems

    • The five chapters in Part II focus on scaling request processing.
    • Major topics covered include: scaling out systems across multiple compute resources, load balancing, distributed caching, asynchronous messaging, and microservice-based architectures.
    • Basic concepts of these architectural approaches are introduced, illustrated with examples from widely used distributed technologies like RabbitMQ and Google App Engine.

    Chapter 5: Application Services

    • The core of any system is the unique business logic that implements application requirements.
    • In distributed systems, this logic is exposed to clients through APIs and executed within a runtime environment that supports concurrent remote calls efficiently.
    • An API and its implementation are fundamental elements of the services an application provides.
    • This chapter focuses on achieving scalability for the services tier in an application.
    • APIs, service design, application servers (execution environment for services), horizontal scaling, load balancing, and state management are discussed.

    Service Design

    • An application has one internet facing service, which persists data to a local data store and clients interact through its published API, accessible across the internet. (Figure 5-1)

    Application Programming Interface (API)

    • An API defines a contract between client and server, specifying request types, data, and results.
    • API variations exist, with HTTP APIs being predominant.
    • RESTful APIs, defined by Roy Fielding, are a common style in modern web technologies
    • CRUD (Create, Read, Update, Delete) API examples illustrated (Table 5-1)

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    Description

    This quiz explores Chapter 5 of Part II on Scalable Systems. It covers the unique business logic in distributed systems, focusing on APIs and service design for achieving scalability in application services. Learn about the execution environments, concurrent remote calls, and the importance of APIs in modern architecture.

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