Introduction:
The process of entering a URL into your web browser and hitting Enter might seem like a simple action, but behind the scenes, a complex series of steps takes place to ensure that you can access the requested website. In this blog post, we will demystify the journey of a web request, breaking it down into various components such as DNS, TCP/IP, Firewall, HTTPS/SSL, Load-balancer, Web server, Application server, and Database, to help you understand what happens when you type https://www.google.com and press Enter.
1.DNS Request: Your browser initiates the process by sending a DNS (Domain Name System) request to resolve the human-friendly domain name “www.google.com" into an IP address. The request is sent to a DNS server, which responds with the corresponding IP address (e.g., 172.217.3.164).
The following steps will elaborate the processess of a DNS request.
Domain Name to IP Resolution:
When you enter a URL like “
Local DNS Cache: Your computer doesn’t start by sending a DNS request to a remote DNS server right away. It first checks its local DNS cache. Operating systems and browsers maintain a cache of previously resolved domain names to speed up the process. If you have recently visited the same website, your computer might already have the IP address in its cache, and it can skip the DNS resolution process.
Recursive DNS Query: If the IP address is not found in the local cache or has expired, your computer sends a DNS query to a local DNS resolver (usually provided by your Internet Service Provider, ISP). This resolver may also have its cache to reduce the load on the root DNS servers.
Root DNS Servers: If the local DNS resolver doesn’t have the IP address for “www.google.com," it starts the resolution process by contacting the root DNS servers. These servers are a critical part of the DNS infrastructure and maintain information about the top-level domains (TLDs) like “.com,” “.org,” etc. The root DNS servers don’t know the IP address for specific websites like “www.google.com," but they can direct the query to the authoritative DNS server for the “.com” TLD.
TLD DNS Servers: The query is then forwarded to the TLD DNS servers responsible for the “.com” TLD. The TLD DNS servers maintain information about the name servers responsible for the next level of domains (in this case, “google.com”).
Authoritative DNS Server: The TLD DNS servers return the IP address of the authoritative DNS server for “google.com.” This server is the one that holds the specific IP address information for “www.google.com."
Query to Authoritative DNS Server: The local DNS resolver now queries the authoritative DNS server for “google.com” directly. This server has the accurate and up-to-date IP address information for “www.google.com."
IP Address Response: The authoritative DNS server for “google.com” responds to the resolver with the IP address (e.g., 172.217.3.164) associated with “www.google.com."
Caching and Response to Browser: The local DNS resolver caches the IP address for future reference to expedite subsequent requests to the same domain. It then sends the IP address to your computer’s browser.
Browser Connection: With the IP address in hand, your browser can now initiate a connection to the web server hosting “www.google.com." It uses this IP address to find and communicate with the specific server that will serve the web content you requested.
This process ensures that you can access websites using human-friendly domain names, abstracting away the need to remember numerical IP addresses for every site you visit, and highlights the crucial role that DNS servers play in the functioning of the internet.
2.TCP/IP: Once your browser has the IP address, it uses the Transmission Control Protocol (TCP) to establish a connection with the server. TCP ensures reliable and ordered communication, splitting data into packets that are sent and reassembled in the correct order on the receiving end. Internet Protocol (IP) takes care of routing these packets across the Internet.
IP Address Acquisition: After the DNS resolution process, your browser has obtained the IP address associated with the website you want to visit (e.g., 172.217.3.164 for “www.google.com"). This IP address serves as the destination for the communication.
Transmission Control Protocol (TCP): TCP is a fundamental communication protocol in the TCP/IP suite. It’s responsible for ensuring reliable, ordered, and error-checked communication between your computer (the client) and the web server (the host).
Establishing a Connection:
To initiate a connection, your browser and the web server engage in a three-way handshake. The steps involved are: SYN (Synchronize): Your computer sends a SYN packet to the server to initiate the connection. This packet contains some initial sequence numbers to establish communication. SYN-ACK (Synchronize-Acknowledge): The server responds with a SYN-ACK packet, acknowledging the request and providing its sequence numbers. ACK (Acknowledge): Your computer sends an ACK packet back to the server to confirm that the connection is established. At this point, both sides are ready to communicate.
Reliable Data Transfer: Once the connection is established, data transfer begins. TCP breaks the data into packets and numbers them to ensure ordered delivery. If a packet is lost or corrupted during transmission, the recipient requests retransmission. This guarantees the reliable and complete transfer of data.
Flow Control: TCP also handles flow control, which prevents the sender from overwhelming the receiver with data. Flow control mechanisms allow the receiver to signal when it’s ready to accept more data, preventing congestion and ensuring efficient data transfer.
Port Numbers: TCP uses port numbers to distinguish different services on a single IP address. For example, HTTP typically uses port 80, while HTTPS uses port 443. Your browser includes the appropriate port number in the request to inform the server which service you want to access.
Internet Protocol (IP): While TCP ensures reliable communication and ordered data delivery, IP is responsible for routing data packets across the internet. It manages the addressing and routing of data packets, making sure they reach their destination. Each packet contains the source and destination IP addresses, allowing routers along the way to guide them to the correct location.
Data Packet Routing: Data packets travel through various routers and switches across the internet. Routers determine the best path to forward the packets based on the destination IP address. The ultimate goal is for the packets to reach the web server hosting the website you’re trying to access.
Assembling and Processing: When the data packets arrive at the web server, they are reassembled in the correct order by the TCP protocol. The server processes the request, retrieves the requested web page or data, and prepares it for transmission back to your browser.
Response Transmission: The server uses the same TCP/IP protocols to send the response data back to your computer. It breaks the response into packets, numbers them, ensures their reliable delivery, and hands them off to the IP layer for routing.
Reassembly and Display:
Your browser’s TCP layer reassembles the incoming packets, ensuring that they are in the correct order. Once the data is complete, it hands it over to the browser’s rendering engine, which displays the website on your screen.
In summary, the TCP/IP protocol stack plays a critical role in ensuring that data is reliably and accurately transferred between your computer and web servers across the internet. It manages the establishment of connections, reliable data transfer, addressing, and routing, making modern web browsing a seamless experience.
3.Firewall: The connection between your computer and the web server may pass through firewalls, which are security mechanisms that filter network traffic. Firewalls are designed to protect against unauthorized access and malicious activity.
Network Security:
Firewalls serve as a crucial line of defence in network security. They act as a barrier between your computer (or local network) and the external network, such as the internet. Their primary objective is to control and filter network traffic to prevent unauthorized access and protect against malicious activity.
Packet Filtering:
Firewalls examine incoming and outgoing data packets to determine whether they should be allowed or blocked based on predefined rules. These rules can specify various criteria, including source and destination IP addresses, port numbers, and the type of protocol (TCP, UDP, etc.).
Stateful Inspection:
Modern firewalls often employ stateful inspection, which not only checks individual packets but also keeps track of the state of active connections. This allows the firewall to make informed decisions based on the context of the connection. For example, if your computer initiates an outgoing connection to a web server, the firewall allows incoming responses associated with that connection.
Application Layer Filtering: Some firewalls go beyond packet filtering and perform deep packet inspection (DPI) at the application layer. This means they can analyze the content of data packets to identify specific applications or protocols. For instance, they can identify HTTP traffic and inspect the content of web requests and responses to detect threats or unauthorized access.
Port Blocking: Firewalls can block or restrict access to specific ports on your computer or network. This is especially important in preventing attacks that target known vulnerabilities associated with certain ports. For example, a firewall can block incoming traffic on port 22, which is commonly used for SSH, to prevent unauthorized access to your system.
Intrusion Detection and Prevention: Some advanced firewalls include intrusion detection and prevention systems (IDPS) that monitor network traffic for suspicious patterns or known attack signatures. If an attack is detected, the firewall can take proactive measures, such as blocking the source of the attack or alerting network administrators.
Application Control: In addition to port-based filtering, firewalls can enforce policies related to specific applications. This can include blocking or restricting access to certain websites, applications, or services that might pose security risks or violate company policies.
Network Segmentation: Firewalls are commonly used to segment networks into zones, each with different security policies. For instance, a company might have a demilitarized zone (DMZ) where publicly accessible servers are placed, and another zone for internal resources. Firewalls control the traffic between these zones to prevent unauthorized access to critical assets.
Logging and Reporting: Firewalls log information about network traffic, including allowed and denied connections. This data can be crucial for auditing and analysing security incidents. Many firewalls provide reporting capabilities to help administrators track network activity.
Security Policies: Firewalls are configured with security policies that define the rules and settings for filtering network traffic. Administrators must carefully craft and maintain these policies to ensure the firewall effectively protects the network.
In summary, firewalls are integral to network security, acting as gatekeepers that filter and control traffic between your computer or network and the broader internet. They enforce policies to protect against unauthorized access, threats, and malicious activity, making them a vital component in safeguarding digital assets and data.
4.HTTPS/SSL: In the case of “https://www.google.com," the ‘https’ indicates that the connection is secure, and SSL (Secure Sockets Layer) or its successor TLS (Transport Layer Security) is used to encrypt the data transmitted between your browser and the server. This encryption ensures that your data remains confidential and secure.
HTTP vs. HTTPS:
HTTP (Hypertext Transfer Protocol) is the standard protocol for transferring data over the web. It’s used for most web pages.
HTTPS (Hypertext Transfer Protocol Secure) is a secure version of HTTP. The ‘s’ stands for ‘secure,’ and it indicates that the communication between your browser and the web server is encrypted and protected.
- Encryption and SSL/TLS:
SSL (Secure Sockets Layer) and its successor, TLS (Transport Layer Security), are cryptographic protocols designed to secure data transmission over the internet.
SSL was the earlier version and has been mostly replaced by TLS due to security improvements. However, the term SSL is still commonly used to refer to both protocols.
TLS, specifically versions like TLS 1.2 and TLS 1.3, is the more modern and secure standard.
- Encryption Basics:
When you access a website using HTTPS, your browser and the web server establish a secure connection. This is done through a process known as the SSL/TLS handshake.
During the handshake, both the client (your browser) and the server agree on a set of encryption algorithms and a shared secret key. This key is used to encrypt and decrypt data exchanged between them.
- Data Confidentiality:
The primary benefit of HTTPS is data confidentiality. When you send information, such as login credentials or credit card details, it is encrypted. This means that even if a malicious actor intercepts the data during transmission, they won’t be able to read it without the decryption key.
Data Integrity: HTTPS also ensures data integrity. It uses digital signatures to verify that the data hasn’t been tampered with during transmission. If any modification occurs, the data becomes invalid, and the connection is terminated.
Authentication and Trust:
HTTPS employs digital certificates issued by trusted entities known as Certificate Authorities (CAs). These certificates contain the public key of the website, which can be used to encrypt data, and information about the website owner.
When you connect to an HTTPS site, your browser checks the certificate. If it’s valid and issued by a trusted CA, your browser establishes the secure connection. If the certificate is invalid or has expired, your browser will warn you about potential security risks.
Visual Indicators:
Browsers often indicate a secure connection with visual cues, such as a padlock icon in the address bar and the URL starting with “https://." These signals reassure users that their data is being protected.
HTTPS Everywhere:
The push for HTTPS everywhere has become a global effort. Many web browsers and search engines prioritize HTTPS websites in search results and flag non-secure sites as potentially unsafe.
SEO and Security:
In addition to security, HTTPS has SEO benefits. Google, for example, considers HTTPS as a ranking factor, giving secure websites an advantage in search results.
Performance:
Modern TLS implementations are designed for speed and efficiency. The overhead of encryption is minimal, and the performance impact is almost negligible, making it a practical choice for all websites.
In summary, HTTPS/SSL (or TLS) is a security protocol that ensures the confidentiality, integrity, and authenticity of data transmitted between your browser and a web server. It provides a secure and encrypted channel for sensitive information, protecting users from eavesdropping and data tampering while browsing the web.
5.Load-Balancer: Google serves billions of requests daily, and to manage the load efficiently, they use load balancers. Load balancers distribute incoming web traffic across multiple servers to ensure that no single server is overwhelmed. This enhances the website’s availability and performance.
Traffic Distribution: Load balancers act as intermediaries between client devices (e.g., web browsers) and backend servers. When a user sends a request to access a website or service, the load balancer intercepts this request. It then determines which backend server should handle the request, based on a set of predefined rules and algorithms. These rules can include factors like server health, server load, or the geographical location of the user.
Even Load Distribution: One of the primary goals of load balancing is to ensure even distribution of traffic across all available servers. This helps prevent any single server from becoming overwhelmed, which could lead to performance degradation or downtime. Distributing the load effectively maximizes the resources and capacity of the server infrastructure.
High Availability: Load balancers are configured to check the health and status of servers in the backend pool. If a server becomes unresponsive or fails, the load balancer automatically redirects traffic away from the problematic server to healthy ones. This enhances the overall availability of the service. In Google’s case, this is crucial because they serve billions of requests daily, and any downtime could have a significant impact.
Scalability: As traffic patterns fluctuate throughout the day, load balancers allow for easy scalability. New servers can be added to the backend pool or taken out as needed, without affecting the user experience. This flexibility is vital for handling the varying demands on a global platform like Google.
Security: Load balancers can also provide security benefits. They can be configured to filter out malicious traffic, distribute SSL encryption, and hide the internal server structure from external users, which adds an extra layer of protection to the infrastructure.
Performance Optimization: Load balancers can optimize the performance of a website or application by directing user requests to the server that can respond most efficiently. This ensures that users experience faster response times and better overall performance.
Global Load Balancing: For global services like Google, load balancers can distribute traffic to servers in data centre located around the world. This is especially important for content delivery and ensuring that users receive data from servers that are geographically closer to them. Google employs global load balancing to improve the user experience for people accessing its services from different parts of the world.
In summary, load balancers are a fundamental part of Google’s infrastructure, as well as many other large-scale online services. They play a critical role in maintaining high availability, optimizing performance, and ensuring the efficient use of server resources. Without load balancing, handling the massive daily traffic that Google receives would be much more challenging, and the user experience could suffer.
6.Web Server: After passing through the load balancer, the request reaches one of Google’s web servers. These servers process your request, fetching the requested web page or data from Google’s databases.
A web server is a software application or a physical server that receives, processes, and fulfils client requests for web resources, typically over HTTP or HTTPS.
Web servers are responsible for handling incoming requests, generating responses, and delivering web content to clients like web browsers.
When your browser initiates a request by typing a URL or clicking on a link, the request travels over the internet, passes through the load balancer (if used), and eventually reaches one of Google’s web servers.
The web server receives the request, which includes information about the requested resource, the HTTP method (e.g., GET for retrieving a webpage), and additional headers.
The web server processes the request to determine which resource is being sought. In Google’s case, this could be a search result page, an image, a video, or any other web content.
If the requested resource is a static file (e.g., an HTML page or an image), the web server can directly retrieve and serve it to the client. If it’s dynamic content (e.g., search results), the server might need to communicate with other components, such as application servers and databases.
Web servers can execute server-side scripts or applications that generate dynamic content in response to client requests. These scripts are often written in languages like PHP, Python, Ruby, or Node.js.
In Google’s case, the web server can call on various services and algorithms to produce search results in real-time.
Web servers may generate content on-the-fly or fetch precomputed content from a cache. Caching frequently requested data helps improve response times and reduce the load on the web server.
Google, for example, relies heavily on caching to provide search results quickly.
Once the web server has gathered or generated the necessary data, it constructs an HTTP response, including headers and the response body.
The response typically includes metadata like content type, cache directives, and status codes (e.g., 200 OK for a successful request)
The web server sends the response back to the client (your browser) over the established secure connection (in the case of HTTPS).
The response travels through the same network path it took when the request was initiated but in the reverse direction.
After sending the response, the web server typically keeps the connection open for a brief period (keep-alive) in case the client requests additional resources or interactions. This helps reduce connection overhead for subsequent requests.
Web servers often log each incoming request and response. This data can be invaluable for troubleshooting issues, monitoring traffic, and analysing server performance.
Load Balancing and Scalability: High-traffic websites like Google use load balancers to distribute incoming requests across multiple web servers. This load balancing enhances the website’s availability and scalability. If one server is busy or experiences issues, the load balancer can redirect requests to other servers.
In summary, web servers play a central role in processing client requests and serving web content. They are responsible for handling incoming requests, retrieving or generating content, constructing responses, and delivering them to clients. Whether serving static files or generating dynamic content, web servers are a critical part of web infrastructure, working in tandem with other components like application servers and databases to provide a seamless web experience.
7.Application Server: In the case of dynamic content, the web server communicates with an application server. The application server processes requests for applications, databases, or other resources. In Google’s case, this can involve running various services and algorithms to provide search results, ads, and more.
Dynamic Content Handling: When a web server receives a request for dynamic content, such as a user submitting a search query on Google, it needs more than just static HTML files. Dynamic content is generated on the fly based on user input or other variables, and this is where the application server comes into play.
Communication Between Web Server and Application Server: The web server acts as the initial point of contact for a user’s request. However, instead of directly generating the dynamic content, it communicates with an application server. This communication between the web server and application server is typically done through standardized communication protocols like HTTP or Fast CGI.
Processing User Requests: The application server’s primary role is to process the user’s request, which could involve complex operations. In the case of Google, this might mean processing a search query. The application server takes the input data (e.g., the search query), processes it, and executes the necessary logic to generate a response.
Database Interaction: In many cases, application servers interact with databases to retrieve or update information. For Google, this could mean querying its massive database of web pages and other content to provide search results. Application servers can handle database connections, query optimization, and data retrieval, ensuring that the requested information is retrieved quickly and accurately.
Algorithms and Services: Google’s application servers run various algorithms and services to provide its core offerings. For example, they might run complex ranking algorithms to determine the most relevant search results, or they might serve ads through specialized services. The application server coordinates these algorithms and services to generate the final response to the user.
Response Generation: Once the application server has processed the request, retrieved data from databases, and executed necessary algorithms, it generates a dynamic response. This response can include HTML content, search results, personalized recommendations, or any other data required to fulfil the user’s request.
Return to the Web Server: The dynamic response generated by the application server is sent back to the web server, which, in turn, sends it to the user’s web browser. The user then sees the final, dynamically generated content.
Load Balancing for Application Servers: Just as load balancers distribute traffic among web servers, they can also distribute requests to multiple application servers. This ensures that the processing load is evenly distributed and that there is redundancy in case one application server experiences issues.
In Google’s case, application servers play a central role in handling the complex operations required for search, advertising, and other services. They process millions of queries and user interactions each day, making it possible for users to access up-to-date and personalized content quickly and efficiently. Without application servers, dynamic and data-driven services like Google Search would not be possible.
8.Database: Google’s services may need to access data stored in databases. Databases are used to store, organize, and retrieve information efficiently. These databases can be responsible for fetching the search results, user data, and other content requested by your browser.
Data Storage and Organization: Databases are like organized warehouses for information. They store vast amounts of data in an organized and structured manner. Google’s services rely on databases to store a wide array of information, such as web pages, user profiles, historical search data, and more.
Efficient Data Retrieval: Databases are designed for efficient data retrieval. When you perform a Google search, the search engine needs to fetch results from its extensive index of web pages. Databases are optimized for quick and precise data retrieval, making it possible for Google to retrieve and present search results to users in a fraction of a second.
Structured Data: Most databases use a structured data model, which means data is organized into tables with predefined schemas. This structure allows Google to categorize, sort, and filter data effectively. For example, it enables Google to search for specific keywords in web pages or filter user data to provide personalized recommendations.
Data Consistency: Databases ensure data consistency by enforcing rules and constraints. This is crucial for Google, especially for services like Google Drive or Google Docs, where multiple users collaborate on the same document simultaneously. Databases prevent conflicts and ensure that changes are made in a coordinated and consistent manner.
Data Security: Protecting user data is a top priority for Google. Databases offer features for securing data, including access control, encryption, and auditing. Google uses these features to protect sensitive user information and maintain trust.
Scalability: Google’s databases must be highly scalable to handle the enormous amount of data generated daily. They use distributed databases and data shading techniques to ensure that as data volume increases, the system can grow horizontally by adding more servers and storage capacity.
Redundancy and Failover: To ensure high availability and data integrity, Google uses database replication and failover strategies. In the event of a hardware failure or other issues, data can be seamlessly switched to another server or data centre. This redundancy minimizes the risk of data loss and service disruptions.
Query Optimization: Google has to deal with complex queries, especially for services like Google Search. Databases use query optimization techniques to ensure that searches are performed as efficiently as possible. This includes indexing, caching, and query rewriting to speed up search operations.
Data Analytics: Google also employs databases for data analytics and business intelligence. They analyse vast amounts of user data to understand user behaviour, improve services, and make informed business decisions.
Data Maintenance: Databases require regular maintenance, such as backup and data cleaning. Google has to maintain its databases to ensure data integrity, performance, and availability.
In summary, databases are a foundational component of Google’s infrastructure. They are responsible for storing, managing, and delivering data efficiently to power services like Google Search, Gmail, Google Maps, and many others. Databases enable Google to handle the massive scale of data and queries that they receive daily while providing users with fast and reliable access to information.
Conclusion: Typing “https://www.google.com" and hitting Enter triggers a remarkable series of steps that involve DNS resolution, establishing a TCP/IP connection, passing through firewalls, enabling HTTPS/SSL encryption, load-balancing, web servers, application servers, and databases. Understanding this process provides insight into the complexity of the web infrastructure and the numerous components working together to deliver the web content you request. It also serves as a reminder of the impressive technology and engineering that powers our daily web interactions.
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