Podcast
Questions and Answers
What HTTP verb is used to delete a skier's profile?
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?
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?
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?
What does the URI '/skico.com/skiers/768934' represent?
When making an API call to put a new city for a skier, what must the client provide?
When making an API call to put a new city for a skier, what must the client provide?
What is typically the format for payloads in HTTP requests?
What is typically the format for payloads in HTTP requests?
Which HTTP verb indicates the intention to retrieve a resource?
Which HTTP verb indicates the intention to retrieve a resource?
In the context of HTTP APIs, how are resources generally identified?
In the context of HTTP APIs, how are resources generally identified?
What is the primary purpose of an API in a distributed system?
What is the primary purpose of an API in a distributed system?
Which of the following features is NOT typically associated with application servers?
Which of the following features is NOT typically associated with application servers?
What is horizontal scaling?
What is horizontal scaling?
Which term describes a system design that allows services to operate independently and communicate over a network?
Which term describes a system design that allows services to operate independently and communicate over a network?
What is the role of load balancing in scalable systems?
What is the role of load balancing in scalable systems?
In terms of application services, what does state management refer to?
In terms of application services, what does state management refer to?
What best describes distributed caching?
What best describes distributed caching?
Which of the following is a benefit of asynchronous messaging in distributed systems?
Which of the following is a benefit of asynchronous messaging in distributed systems?
What is the primary reason for utilizing a fixed-size database connection pool in servlets?
What is the primary reason for utilizing a fixed-size database connection pool in servlets?
How does a servlet obtain a connection from the database connection pool?
How does a servlet obtain a connection from the database connection pool?
What occurs when a servlet requests a connection but the connection pool is full?
What occurs when a servlet requests a connection but the connection pool is full?
What can cause request response time to increase in a servlet processing environment?
What can cause request response time to increase in a servlet processing environment?
What can happen if a server experiences high load and has limited resources?
What can happen if a server experiences high load and has limited resources?
What impact does context switching have on server performance in a heavily loaded environment?
What impact does context switching have on server performance in a heavily loaded environment?
What configuration aspects can be adjusted in an application server like Tomcat to optimize performance?
What configuration aspects can be adjusted in an application server like Tomcat to optimize performance?
What resource affects the processing capacity of a Tomcat container?
What resource affects the processing capacity of a Tomcat container?
What is the main reason adding more traffic lanes might not alleviate traffic chaos?
What is the main reason adding more traffic lanes might not alleviate traffic chaos?
What role do services play in a scalable software system?
What role do services play in a scalable software system?
What happens when all threads in an application server's thread pool are utilized?
What happens when all threads in an application server's thread pool are utilized?
What is the benefit of scaling services out horizontally using a load balancer?
What is the benefit of scaling services out horizontally using a load balancer?
Why are stateless services recommended for scalable architectures?
Why are stateless services recommended for scalable architectures?
What is the primary benefit of horizontal scaling?
What is the primary benefit of horizontal scaling?
What is a feature of load balancers that can support stateful services?
What is a feature of load balancers that can support stateful services?
Why must servers be stateless in a horizontally scaled system?
Why must servers be stateless in a horizontally scaled system?
What is a complexity associated with stateful services as compared to stateless services?
What is a complexity associated with stateful services as compared to stateless services?
What happens if a load balancer routes requests to stateful services incorrectly?
What happens if a load balancer routes requests to stateful services incorrectly?
How does increased availability relate to having multiple replicas in a system?
How does increased availability relate to having multiple replicas in a system?
What is one drawback of relying solely on technology suppliers' documentation for load balancer knowledge?
What is one drawback of relying solely on technology suppliers' documentation for load balancer knowledge?
What is the role of the load balancer in a horizontally scaled system?
What is the role of the load balancer in a horizontally scaled system?
What is a single point of failure (SPoF) and why is it undesirable?
What is a single point of failure (SPoF) and why is it undesirable?
What technology can externalize session state, making services stateless?
What technology can externalize session state, making services stateless?
What is a crucial factor for a scalable system to be effective?
What is a crucial factor for a scalable system to be effective?
HTTP is known as a stateless protocol, meaning each request is executed independently.
HTTP is known as a stateless protocol, meaning each request is executed independently.
Conversational state refers to information that is lost between requests.
Conversational state refers to information that is lost between requests.
Server implementations that need to scale should store conversational state.
Server implementations that need to scale should store conversational state.
A servlet can obtain a connection from a database connection pool multiple times without issues.
A servlet can obtain a connection from a database connection pool multiple times without issues.
If a request is poorly formatted, the server will return a 200 status code.
If a request is poorly formatted, the server will return a 200 status code.
State management in application services refers to the technique of retaining data across multiple requests.
State management in application services refers to the technique of retaining data across multiple requests.
The skierID should be extracted from the request URI to handle requests correctly.
The skierID should be extracted from the request URI to handle requests correctly.
HTTP requests must always contain sufficient information for the server to satisfy the request regardless of previous interactions.
HTTP requests must always contain sufficient information for the server to satisfy the request regardless of previous interactions.
A stateful service retains conversational state from previous requests.
A stateful service retains conversational state from previous requests.
A PUT request to update a skier's profile does not require the unique identifier of the resource.
A PUT request to update a skier's profile does not require the unique identifier of the resource.
Stateless services do not hold any information about earlier requests.
Stateless services do not hold any information about earlier requests.
Using a stateful service can increase the amount of data passed between clients and services.
Using a stateful service can increase the amount of data passed between clients and services.
In a stateful service, each request requires the client to provide all required information for processing.
In a stateful service, each request requires the client to provide all required information for processing.
When a user logs in, a session state object is often created to track their interactions.
When a user logs in, a session state object is often created to track their interactions.
Managing conversational state is less complex than handling stateless services.
Managing conversational state is less complex than handling stateless services.
Stateful services are recommended primarily for applications with high traffic loads.
Stateful services are recommended primarily for applications with high traffic loads.
An application server is responsible for accepting requests from clients and applying application logic to the requests.
An application server is responsible for accepting requests from clients and applying application logic to the requests.
The Java Enterprise Edition (JEE) is a lightweight framework specifically designed for application servers.
The Java Enterprise Edition (JEE) is a lightweight framework specifically designed for application servers.
Stateless APIs are crucial for scalable services to retain state pertaining to client sessions.
Stateless APIs are crucial for scalable services to retain state pertaining to client sessions.
Apache Tomcat is an open-source implementation of a portion of the JEE platform.
Apache Tomcat is an open-source implementation of a portion of the JEE platform.
In the context of application servers, Flask is a server that supports Ruby.
In the context of application servers, Flask is a server that supports Ruby.
Horizontal scaling involves adding additional servers to handle increased traffic.
Horizontal scaling involves adding additional servers to handle increased traffic.
Express.js is a framework used for building applications in the Java programming language.
Express.js is a framework used for building applications in the Java programming language.
External data stores are used to retain state for services that must retain client session information.
External data stores are used to retain state for services that must retain client session information.
Node.js is a multiple-threaded environment that does not support asynchronous programming.
Node.js is a multiple-threaded environment that does not support asynchronous programming.
Tony Bourke's book, Server Load Balancing, is a useful resource for understanding the field of load balancing.
Tony Bourke's book, Server Load Balancing, is a useful resource for understanding the field of load balancing.
The Apache Tomcat Executor does not have any default configuration settings.
The Apache Tomcat Executor does not have any default configuration settings.
Experiments by Ruijie Xiao were conducted at Northeastern University in Boston.
Experiments by Ruijie Xiao were conducted at Northeastern University in Boston.
A broad perspective on load balancing can be gained from the work of Roy T. Fielding.
A broad perspective on load balancing can be gained from the work of Roy T. Fielding.
A load balancer will consistently send requests to a service that is unresponsive.
A load balancer will consistently send requests to a service that is unresponsive.
Elasticity allows a service to dynamically reduce its capacity as request loads decrease.
Elasticity allows a service to dynamically reduce its capacity as request loads decrease.
Health checks by the load balancer involve sending requests at random intervals.
Health checks by the load balancer involve sending requests at random intervals.
A service replica assigned a weight of 2 will receive fewer requests than a replica assigned a weight of 1.
A service replica assigned a weight of 2 will receive fewer requests than a replica assigned a weight of 1.
Scaling policies can only be defined using CPU metrics in a load balancer.
Scaling policies can only be defined using CPU metrics in a load balancer.
An Auto Scaling group maintains a fixed number of service instances regardless of load changes.
An Auto Scaling group maintains a fixed number of service instances regardless of load changes.
A transient failure in a service will lead to its permanent removal from the load balancer's target pool.
A transient failure in a service will lead to its permanent removal from the load balancer's target pool.
Load balancers require a tight integration with application monitoring to achieve elasticity.
Load balancers require a tight integration with application monitoring to achieve elasticity.
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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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.
