System Design Review
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What is synchronous replication?

  • The primary node waits for acknowledgments from secondary nodes. (correct)
  • The primary node discards data updates.
  • The primary node reports success to the client immediately.
  • The primary node does not wait for acknowledgments from secondary nodes.

    • What is an advantage of asynchronous replication?

  • All secondary nodes are completely up to date.
  • It guarantees low latency.
  • The primary node can continue its work even if all secondary nodes are down. (correct)
  • It ensures data integrity.

    • What is partitioning?

    Partitioning is the process of dividing a large dataset into smaller chunks stored at different nodes to balance the load.

    Synchronous replication requires __________ from secondary nodes.

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

    Which of the following is a type of horizontal partitioning?

    <p>Key-range based partitioning</p> Signup and view all the answers

    Vertical partitioning involves splitting a table into multiple tables based on rows.

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

    What are key-value stores?

    <p>Key-value stores are a type of distributed data storage model that binds unique keys to specific values.</p> Signup and view all the answers

    What is one of the main functional requirements of key-value stores?

    <p>The ability to always write data into the key-value storage.</p> Signup and view all the answers

    A Content Delivery Network (CDN) consists of a single server.

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

    What is the primary purpose of a CDN?

    <p>The primary purpose of a CDN is to improve content delivery speed and reduce latency for end users.</p> Signup and view all the answers

    What is the Domain Name System (DNS)?

    <p>The DNS is the Internet's naming service that maps human-friendly domain names to machine-readable IP addresses.</p> Signup and view all the answers

    Which of the following are types of DNS hierarchy servers? (Select all that apply)

    <p>DNS Resolver</p> Signup and view all the answers

    DNS uses a hierarchical structure for its name servers.

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

    What is caching in the context of DNS?

    <p>Caching refers to the temporary storage of frequently requested resource records to reduce response time and decrease network traffic.</p> Signup and view all the answers

    What happens to the DNS if the time-to-live (TTL) value is set too large?

    <p>Users will receive outdated information longer.</p> Signup and view all the answers

    What is the primary function of a load balancer?

    <p>To fairly divide client requests among available servers to avoid overloading any single server.</p> Signup and view all the answers

    Load balancers are considered a single point of failure (SPOF).

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

    DNS names are processed from the ______ to ______.

    <p>right, left</p> Signup and view all the answers

    What protocol does DNS typically use for query messages?

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

    Match the following DNS terminologies with their descriptions:

    <p>DNS Resolver = Initiates queries and forwards them to other DNS servers Root-level Name Servers = Receive requests from local servers Authoritative Name Servers = Provide IP addresses of web servers Caching = Temporary storage of resource records</p> Signup and view all the answers

    Why does the DNS use load balancing?

    <p>To distribute client requests to multiple servers to ensure availability and enhance performance.</p> Signup and view all the answers

    Why is a dedicated monitoring solution necessary in a distributed system?

    <p>To provide centralized visibility, detect correlations that individual logs would miss, and enable proactive alerts for faster troubleshooting.</p> Signup and view all the answers

    Which of the following is not included in server monitoring?

    <p>Monitoring user activity</p> Signup and view all the answers

    Monitoring network links and paths' latency is important for identifying bottlenecks.

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

    The high-level components of our monitoring service include storage and a data ______ service.

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

    What is the purpose of a time-series database in a monitoring service?

    <p>To store metrics data such as CPU usage or the number of exceptions.</p> Signup and view all the answers

    Which cloud service provider does not provide a health status page as mentioned in the content?

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

    What type of monitoring involves ensuring efficient communication and connectivity for external clients?

    <p>Network monitoring</p> Signup and view all the answers

    What should be excluded when testing the service's standard functionality?

    <p>Active probing</p> Signup and view all the answers

    Which component of a CDN is responsible for directing clients to the nearest CDN facility?

    <p>Routing system</p> Signup and view all the answers

    Scrubber servers are used to distribute content to edge proxy servers.

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

    What do origin servers provide to clients?

    <p>Data that is unavailable at the CDN</p> Signup and view all the answers

    The component responsible for distributing content across CDN proxy servers is called the ______.

    <p>distribution system</p> Signup and view all the answers

    Match the following CDN methods with their descriptions:

    <p>Push CDN = Content is sent automatically from the origin server to proxy servers. Pull CDN = CDN retrieves unavailable data from origin servers when requested. Anycast = Routing methodology sharing a single IP address across multiple edge servers. Client multiplexing = Client receives a list of candidate servers to choose from.</p> Signup and view all the answers

    What is one of the main benefits of the pull CDN model?

    <p>Improved storage consumption</p> Signup and view all the answers

    Dynamic content caching optimization can enhance performance by executing scripts at proxy servers.

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

    What is the purpose of a management system in a CDN?

    <p>To observe resource usage and statistics</p> Signup and view all the answers

    A unique ID generation system within a distributed system provides ______ for identifying events and objects.

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

    Which of the following methods takes both network distance and request load into consideration to reduce latency?

    <p>DNS redirection</p> Signup and view all the answers

    What does Geographic Sharding involve?

    <p>Allocating ranges based on data center location</p> Signup and view all the answers

    What is the maximum number of IDs that can be generated in a day?

    <p>86400000</p> Signup and view all the answers

    The ID-generating server is a single point of failure (SPOF).

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

    What approach is taken in a proactive method of handling IT infrastructure failures?

    <p>Preventing downtimes before they occur.</p> Signup and view all the answers

    What is one of the issues with using physical clocks for time measurement?

    <p>They can drift away by 17 seconds per day.</p> Signup and view all the answers

    Metrics can be defined as ___ that provide insight into the system.

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

    What are two conventional approaches to handling failures in IT infrastructure?

    <p>Reactive and proactive approaches.</p> Signup and view all the answers

    What does logging help in monitoring?

    <p>Stores CPU usage and application-related information</p> Signup and view all the answers

    What is one issue that can occur with probers?

    <p>Incomplete coverage or lack of user imitation.</p> Signup and view all the answers

    Pushing metrics is always preferred over pulling metrics.

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

    How can user privacy be protected in client-side monitoring?

    <p>By allowing users to control what data is collected and sent.</p> Signup and view all the answers

    What is local load balancing?

    <p>Local load balancers reside within a datacenter and divide incoming requests among the pool of available servers.</p> Signup and view all the answers

    Which algorithm forwards each request to a server in a repeating sequential manner?

    <p>Round-robin scheduling</p> Signup and view all the answers

    In a weighted round-robin algorithm, what is used to determine server allocation?

    <p>Weights assigned to nodes</p> Signup and view all the answers

    Dynamic algorithms maintain state by communicating with the server.

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

    What is a key difference between stateful and stateless load balancing?

    <p>Stateful load balancing maintains session information, while stateless load balancing does not.</p> Signup and view all the answers

    What layer do Layer 7 load balancers operate on?

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

    What does ACID stand for in relational databases?

    <p>Atomicity, Consistency, Isolation, Durability.</p> Signup and view all the answers

    What do NoSQL databases primarily support?

    <p>Large volumes of semi-structured and unstructured data</p> Signup and view all the answers

    A database is an organized collection of ______.

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

    What is data replication?

    <p>Data replication is keeping multiple copies of the data at various nodes to achieve availability, scalability, and performance.</p> Signup and view all the answers

    What is a common use case for key-value databases?

    <p>Storing data in key-value pairs for fast access</p> Signup and view all the answers

    Study Notes

    Domain Name System (DNS)

    • DNS is the Internet’s naming service, translating human-friendly domain names to machine-readable IP addresses.
    • Users request IP addresses via browsers, prompting queries to DNS infrastructure.
    • The DNS operates as a distributed system with multiple name servers rather than a single server.
    • Resource records (RRs) are used to store domain name to IP address mappings in the DNS database.
    • Types of resource records include type, name, and value; these vary by record type.

    DNS Hierarchy

    • DNS resolvers initiate query sequences and reside within user networks, sometimes employing caching.
    • Root-level name servers maintain servers based on top-level domains (TLDs) like .com, .edu.
    • Top-level domain name servers hold IP addresses for authoritative name servers of specific organizations.
    • Authoritative name servers provide IP addresses of web or application servers.
    • DNS names are processed right to left, contrasting with UNIX file processing.

    Query Resolution Methods

    • Two types of DNS query resolutions exist:
      • Iterative: Local server queries root, TLD, and authoritative servers sequentially.
      • Recursive: Local server handles requests for the user, querying higher-level servers.
    • Iterative queries are generally preferred due to lower load on DNS infrastructure.

    Caching in DNS

    • Caching temporarily stores frequently requested RRs, improving response time and reducing network traffic.
    • Caching can occur at various levels, such as browsers, operating systems, and local name servers.
    • TTL (Time to Live) values should be small to foster high availability and quick updates to resource records.

    DNS Reliability and Scalability

    • DNS reliability is bolstered through caching, server replication, and utilizing UDP for fast performance.
    • There are 13 logical root name servers globally managed by multiple organizations, ensuring reliability and low latency.
    • The DNS is highly scalable, with numerous replicated instances managing user queries effectively.

    Load Balancers

    • Load balancers distribute client requests among servers to prevent overload and ensure high performance.
    • They can enhance scalability, availability, and resource utilization.
    • Key functions include health checking, TLS termination, predictive analytics, and mitigating DoS attacks.
    • Load balancers can fail; hence they are often deployed in pairs or clusters for high availability.

    Global Server Load Balancing (GSLB)

    • GSLB distributes traffic across geographical regions and reroutes during datacenter failures.
    • Decisions are made based on geographic location and datacenter health.
    • GSLB can be implemented on-premises or through Load Balancing as a Service (LBaaS).

    Load Balancing in DNS

    • DNS can respond with multiple IP addresses, using techniques like round-robin for load balancing.
    • Round-robin visits IPs in a circular order but can lead to issues like uneven load distribution if not managed.
    • DNS uses short TTL for caching to improve load balancing effectiveness.

    Local Load Balancing

    • Local load balancers operate within datacenters as reverse proxies to manage incoming requests efficiently.
    • Common algorithms include:
      • Round-robin: Sequentially forwards requests to servers.
      • Weighted round-robin: Prioritizes servers based on assigned weight.
      • Least connections: Assigns requests to servers based on current connections.
      • Least response time: Selects the server with the quickest response time.
      • IP hash: Sorts requests based on users’ IP addresses for tailored service.### URL Hashing and Load Balancing Algorithms
    • URL hashing allocates requests to specific server clusters based on the client's service request URL.
    • Load balancing algorithms can be categorized as static or dynamic, where static ones don't account for the changing state of servers.
    • Dynamic algorithms adapt to the current state of servers, improving forwarding decisions but adding communication overhead among load balancers.

    Stateful vs Stateless Load Balancing

    • Stateful load balancing maintains session information, which can increase complexity and reduce scalability.
    • Stateless load balancing is faster and lightweight, typically using consistent hashing for request forwarding.
    • Stateful load balancers share state across multiple instances, while stateless ones may require local states only for operational purposes.

    Types of Load Balancers

    • Layer 4 load balancers operate based on transport protocols like TCP/UDP, maintaining connections to forward sessions consistently.
    • Layer 7 load balancers make application-aware routing decisions based on HTTP headers, cookies, and user data, enabling features like rate limiting.

    Databases in Distributed Systems

    • Simple file storage is limited in scalability and concurrent access, leading to the need for databases.
    • Databases, structured collections of data, simplify the storage, retrieval, modification, and deletion of information.

    Database Types

    • Relational Databases (SQL): Use structured schemas and SQL for queries; maintain relationships through primary and foreign keys, enforcing ACID properties.
    • Non-Relational Databases (NoSQL): No fixed structure; suitable for unstructured and semi-structured data, offering flexibility and handling large volumes of data.

    Importance of Databases

    • Manage large datasets effectively; ensure data consistency and integrity with constraints; support easy updates and provide robust security measures.
    • Replication capabilities allow high availability and disaster recovery through data duplication across servers.

    Advantages of Relational Databases

    • Enable flexibility in data modification without downtime; reduce redundancy through normalization to enhance data integrity.
    • Handle concurrency, providing error management for simultaneous data access.

    Characteristics of NoSQL Databases

    • Simple designs allow for less code and easier maintenance; horizontal scaling allows for running databases across large clusters, enhancing availability.
    • Support for unstructured data makes NoSQL databases adaptable to diverse data needs, which can include dynamic schemas.

    Types of NoSQL Databases

    • Key-Value Stores: Utilize unique key-value pairs for efficient data access; examples include Redis and Amazon DynamoDB.
    • Document Databases: Store semi-structured documents (e.g., JSON, XML) maintaining a hierarchical structure; MongoDB is a well-known example.
    • Graph Databases: Represent data as nodes and edges to illustrate relationships dynamically, aiding in complex data queries; examples are Neo4J and InfiniteGraph.
    • Columnar Databases: Focus on column-wise data storage for fast access and efficiency; popular ones include Cassandra and HBase.

    Data Replication and Partitioning

    • Replication maintains multiple data copies to ensure availability under varying conditions while improving scalability and performance.
    • Synchronous replication requires acknowledgment from all nodes before confirming updates, while asynchronous replication allows primary nodes to operate independently of secondary nodes.

    Partitioning Techniques

    • Vertical Partitioning: Separates tables into different instances to manage large datasets efficiently, optimizing for specific access patterns.
    • Horizontal Partitioning (Sharding): Distributes rows of a table into smaller segments, reducing latency and ensuring balanced load across nodes.

    Conclusion

    • Load balancers and databases are crucial for efficiently managing internet traffic and data storage, enabling scalability and consistent performance across applications.
    • The distinction between different types of load balancing and database management approaches aids in selecting the appropriate solutions for specific application requirements.### Strategies for Horizontal Partitioning
    • Key-range based partitioning assigns continuous ranges of keys to partitions.
    • Hash-based partitioning applies a hash function to an attribute, producing varying hash values that determine partition allocation.
    • Consistent hashing, list-based, and round-robin are additional horizontal sharding techniques.

    Importance of Databases

    • Efficiently manage large data volumes while ensuring consistency through constraints.
    • Facilitate easy data updates and provide robust security measures.
    • Enhance data integrity and high availability through replication.
    • Support scalability and enable efficient data retrieval and backup.

    Key-Value Store Overview

    • Key-value stores function as distributed hash tables with unique keys bound to various values, including blobs or images.
    • Designed to bypass traditional database complexities, focusing on speed and simplicity.

    Functional Requirements of Key-Value Stores

    • Configurable service: Allows trade-offs between consistency, availability, cost, and performance.
    • Always-write capability: Applications must write data consistently.
    • Hardware heterogeneity: Nodes should perform equal tasks.

    Non-Functional Requirements of Key-Value Stores

    • Scalable: Designed to run on numerous servers globally, managing a substantial user base.
    • High availability: Continuous service provision, with configurable availability.
    • Fault tolerance: System remains operational despite component failures.

    Key Differences Between Key-Value Stores and Traditional Databases

    • Key-value stores prioritize simplicity and quick value retrieval, often sacrificing strict consistency for availability and scalability.
    • Suited for unstructured data and scenarios demanding rapid access.

    Scalability in Key-Value Stores

    • Utilize consistent hashing for balanced data distribution across storage nodes.
    • Implement virtual nodes to ensure a uniform load by applying multiple hash functions to each key.

    Data Replication Strategies

    • Employ primary-secondary or peer-to-peer replication methods for data consistency during failures.
    • Utilize vector clocks to maintain causality and manage data versioning across replicas.

    Handling Failures in Key-Value Stores

    • Use Merkle trees to quickly synchronize and detect inconsistencies among replicas.
    • Each node maintains a unique Merkle tree corresponding to its key ranges for efficient checks.

    Promoting Membership for Failure Detection

    • Careful handling of node additions and removals ensures stability.
    • Utilize a gossip protocol for synchronizing membership histories among nodes.

    Content Delivery Network (CDN) Basics

    • CDNs consist of geographically distributed proxy servers to reduce latency and bandwidth.
    • Proxy servers positioned at network edges provide quick content delivery.

    Advantages of CDNs

    • Enhanced content delivery speed and reduced server load.
    • Increased scalability and availability through load distribution.
    • Global reach allowing geo-targeted content delivery.

    Functional Requirements of CDNs

    • Capability to retrieve and deliver content based on user requests.
    • Ability to update and delete cached entries in accordance with content type.

    Non-Functional Requirements of CDNs

    • Minimized latency, ensuring high performance.
    • Continuous availability, protecting against outages and attacks.
    • Reliable handling of massive traffic loads without single points of failure.

    Key Components of a CDN

    • Clients: End users accessing content via various devices.
    • Routing system: Directs clients to the nearest server based on load and content placement.
    • Proxy servers: Store and serve content quickly to users.
    • Scrubber servers: Filter traffic to protect against attacks like DDoS.
    • Distribution system: Distributes content across all proxy servers efficiently.
    • Origin servers: Store original data and provide it when content is unavailable in the CDN.

    CDN Workflow

    • Origin servers publish content to the distribution system.
    • Routing system directs clients to the appropriate proxy server based on cached content.
    • Client requests are scrubbed for security, then routed to the edge proxy server to deliver desired content.

    Push vs. Pull CDN Models

    • Push CDN automatically sends content to proxy servers from origin servers, best for static content.
    • Pull CDN retrieves unavailable data from origin servers per user request and is more suitable for dynamic content.
    • Mixing both models leverages the strengths of each approach for varying content types.

    Dynamic Content Caching Optimization

    • Dynamic content creation may leverage script execution on proxy servers to optimize delivery and processing efficiency.

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