Ever wondered what happens behind the scenes when you type a URL like https://www.google.com into your browser and press Enter? Let's take a journey through the process step by step, covering key aspects like DNS requests, TCP/IP, firewalls, HTTPS/SSL, load balancers, web servers, application servers, and databases.
1. DNS Request
When you type https://www.google.com into your browser, the first step is to translate the human-readable domain name into an IP address that computers can understand. This is where the Domain Name System (DNS) comes into play.
DNS Resolution: Your browser checks its cache to see if it has recently requested this domain. If not, it sends a DNS query to a DNS resolver.
DNS Resolver: The resolver queries various DNS servers, starting with the root DNS server, followed by the top-level domain (TLD) server (.com in this case), and finally, the authoritative DNS server for google.com.
IP Address: The authoritative DNS server returns the IP address associated with www.google.com to your browser.
2. TCP/IP
With the IP address in hand, your browser needs to establish a connection to the server. This is done using the TCP/IP protocol.
TCP Handshake: The browser initiates a TCP connection with Google's server using a three-step handshake process (SYN, SYN-ACK, ACK).
Port: The request is made to the server’s IP address on port 443 (the default port for HTTPS).
3. Firewall
Before the request reaches Google's server, it typically passes through one or more firewalls. Firewalls are security devices designed to monitor and filter incoming and outgoing traffic based on predefined security rules.
Inspection: The firewall inspects the traffic to ensure it meets security criteria.
Pass-through: If the traffic is deemed safe, the firewall allows it to pass through to the server.
4. HTTPS/SSL
HTTPS ensures that the communication between your browser and the server is encrypted, protecting any data exchanged from eavesdroppers.
SSL/TLS Handshake: The browser and the server perform an SSL/TLS handshake to establish a secure connection. This involves exchanging cryptographic keys and verifying certificates.
Encryption: Once the handshake is complete, all data sent between the browser and the server is encrypted.
5. Load Balancer
Google uses load balancers to distribute incoming traffic across multiple servers to ensure no single server becomes overwhelmed.
Distribution: The load balancer receives the incoming request and forwards it to one of the many available web servers, balancing the load based on current traffic.
6. Web Server
The web server is responsible for handling HTTP requests and serving web pages.
Handling the Request: The web server receives the request and determines what content to serve. This could be a static HTML page or it could require dynamic content generation.
7. Application Server
For dynamic content, the web server forwards the request to an application server.
Processing: The application server runs the necessary backend logic, which might involve interacting with various services and components to generate the appropriate response.
8. Database
If the request requires data storage or retrieval, the application server communicates with the database.
Query: The application server sends a query to the database to retrieve or store data.
Response: The database processes the query and sends the results back to the application server.
9. Response Back to Browser
Generate Web Page: The application server generates the HTML for the web page based on the data retrieved from the database.
Send Response: The web server sends the final HTML content back through the load balancer, which forwards it to the client (your browser).
Render Page: Your browser receives the HTML, CSS, JavaScript, and other resources, and renders the web page for you to see.
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