Following our previous discussion on TCP, which ensures reliable data transmission, we now shift our focus to how DNS facilitates efficient and scalable web navigation. We will explore its resolution process, server types, caching mechanisms, and optimization techniques, ensuring a robust understanding of how DNS contributes to modern cloud environments.
The Domain Name System (DNS) serves as the phonebook of the Internet. When humans access information online, they typically use domain names such as http://nytimes.com or http://espn.com. Web browsers then interact through Internet Protocol (IP) addresses. DNS plays a crucial role in translating these domain names to IP addresses, enabling browsers to load Internet resources effectively.
Every device that is connected to the Internet is assigned a unique IP address, which serves as its identifier for communication with other devices. DNS servers play a crucial role in translating domain names into these numerical IP addresses, sparing users from having to remember complex strings of numbers and characters. For example, IPv4 addresses like 192.168.1.1 or more intricate alphanumeric IPv6 addresses such as 2400:cb00:2048:1::c629:d7a2 are managed by DNS servers to simplify accessibility on the web.
The DNS resolution process includes the conversion of a hostname (such as http://www.example.com) into an IP address (such as 192.168.1.1). Each device on the Internet is assigned an IP address, which is essential for locating the corresponding Internet device - similar to how a street address is used to locate a specific home. When a user intends to load a webpage, there needs to be a translation between what the user inputs into their web browser (http://example.com) and the machine-friendly address required to access the http://example.com webpage.
Understanding the process behind DNS resolution requires learning about the various hardware components that a DNS query must pass through. For web browsers, DNS lookup occurs "behind the scenes" and does not require any interaction from the user's computer apart from the initial request.
There are 4 DNS servers involved in loading a webpage:
Both concepts refer to servers (groups of servers) that are integral to the DNS infrastructure, but each performs a different role and lives in different locations inside the pipeline of a DNS query. One way to think about the difference is that the recursive resolver is at the beginning of the DNS query and the authoritative nameserver is at the end.
The recursive resolver plays a crucial role in responding to recursive requests from clients and taking the necessary time to track down DNS records. It achieves this by making a series of requests until it reaches the authoritative DNS nameserver for the requested record, or times out or returns an error if no record is found. Fortunately, recursive DNS resolvers can leverage caching as a data persistence process to minimize the need for multiple requests, thereby serving the requested resource record earlier in the DNS lookup process.
In simple terms, an authoritative DNS server is a server that holds and is responsible for DNS resource records. It serves as the bottom of the DNS lookup chain, responding with the queried resource record to enable web browsers to access websites or other web resources by reaching the necessary IP address. An authoritative nameserver can fulfill queries from its own data without relying on another source, serving as the ultimate source of truth for specific DNS records.
It is important to note that when dealing with a query for a subdomain like foo.genesiscloud.com or blog.genesiscloud.com, an extra nameserver will be included in the sequence following the authoritative nameserver. This additional nameserver is responsible for storing the CNAME record of the subdomain.
Authoritative servers play a crucial role in domain name resolutions within their specific domain. These servers store the accurate name-to-IP address mappings for a given domain, and they are responsible for providing the definitive answer when queried. While caching mechanisms exist to expedite domain name resolutions, it is the authoritative servers that offer the correct and final response. Domain owners or administrators configure their domain's records, but the maintenance and operation of the actual infrastructure (the DNS servers) are often handled by DNS hosting providers or registrars such as Cloudflare, Namecheap, GoDaddy, and others.
In most cases, DNS primarily deals with translating a domain name into the corresponding IP address. Understanding how this process unfolds involves tracing the journey of a DNS lookup from a web browser, through the lookup process, and back again. Let's delve into each step.
Please note that DNS lookup information is often cached either locally within the querying computer or remotely in the DNS infrastructure. A standard DNS lookup comprises 8 steps; however, when information is cached, certain steps are omitted from the process to expedite it. The following example illustrates all 8 steps when no caching occurs.
The 8 steps in a DNS lookup:
After the 8 steps of the DNS lookup have successfully provided the IP address for http://example.com, the browser can proceed to request the web page.
The DNS resolver plays a crucial role in the DNS lookup process. It is responsible for handling the initial client request and initiating a series of queries that ultimately result in translating a URL into the required IP address.
It's important to note that a typical uncached DNS lookup will involve both recursive and iterative queries.
It is crucial to distinguish between a recursive DNS query and a recursive DNS resolver. The query pertains to the request made to a DNS resolver, which necessitates the resolution of the query. A DNS recursive resolver is a computer that receives a recursive query and handles the response by initiating the required requests.
During a typical DNS lookup, three types of queries are involved. By utilizing a combination of these queries, it is possible to optimize the process for DNS resolution and reduce the distance traveled. In an ideal scenario, cached record data will be accessible, enabling a DNS name server to provide a non-recursive query.
There are 3 types of DNS queries:
Caching aims to temporarily store data in a location, leading to enhancements in performance and reliability for data requests. DNS caching specifically entails storing data closer to the requesting client, enabling earlier resolution of DNS queries and reducing the need for additional queries further down the DNS lookup chain. This ultimately improves load times and reduces bandwidth/CPU consumption. DNS data can be cached in various locations, each of which will retain DNS records for a specific amount of time determined by a time-to-live (TTL).
Modern web browsers are configured to automatically cache DNS records for a specific duration. This design choice aims to streamline the process by minimizing the number of steps required to access the cached information and send requests to an IP address. When a DNS record is requested, the browser cache is the primary location examined for the desired record.
To view the status of your DNS cache in Chrome, simply navigate to chrome://net-internals/#dns.
The DNS resolver at the operating system level serves as the penultimate stop within your local environment before a DNS query is transmitted from your device. This process, known as a "stub resolver" or DNS client, is responsible for managing such queries. Upon receiving a request from an application, the stub resolver initially examines its internal cache to determine if it contains the requested record. If not found, it proceeds to dispatch a DNS query (with a recursive flag enabled) beyond the local network to a DNS recursive resolver situated within the Internet service provider (ISP).
When the recursive resolver within the ISP receives a DNS query, it will proceed to verify if the requested host-to-IP-address translation is already stored inside its local persistence layer, just as in previous steps.
The recursive resolver possesses additional functionality based on the types of records stored in its cache.
DNS offers a variety of services that are essential for the smooth operation of the Internet. Here's a visual representation outlining the range of services offered by DNS.
Below, we will outline some of the essential services provided by DNS.
DNS, or Domain Name System, plays a crucial role in maintaining a database of domain names and their associated IP addresses. This mapping is fundamental for enabling devices to find and communicate with each other on the internet.
Consider the domain name "http://www.genesiscloud.com". Host-to-IP address mapping involves determining the IP address associated with this domain, such as "172.67.21.11".
DNS supports a feature commonly known as host aliasing, enabled through CNAME (Canonical Name) records. This allows a single IP address or primary domain name to be associated with multiple domain name aliases.
Let's delve into the process step by step. Consider the primary domain "http://genesiscloud.com". It's important to ensure that your website is accessible not only via "http://genesiscloud.com", but also through various aliases such as "http://www.genesiscloud.com ", "web.genesiscloud.com", and "http://blog.genesiscloud.com". By configuring the appropriate CNAME records in DNS, all these aliases can be directed to the primary domain "http://genesiscloud.com". Consequently, users will be able to access your website using any of these domain names, all leading to the same destination IP address.
DNS plays a vital role in the routing of emails through MX records. These records enable a domain to designate which mail servers are accountable for receiving email messages on its behalf, providing flexibility in email configurations.
For instance, consider the primary mail server assigned to receive emails for the "http://genesiscloud.com" domain as "mail.genesiscloud.com". It may be necessary to create distinct email addresses, such as those ending in "@sales.genesiscloud.com" or "@support.genesiscloud.com", while still directing all incoming mail for these addresses to the "mail.genesiscloud.com" server. By setting up MX records correctly, emails sent to any of these addresses will be directed to the designated primary mail server.
DNS, or Domain Name System, serves as a crucial component in translating domain names to IP addresses. In addition to this primary function, DNS can also conduct reverse lookups by translating IP addresses back to domain names. This capability is particularly valuable for security measures and logging activities.
DNS operates by distributing incoming network traffic across multiple servers through the use of different IP addresses in response to the same domain name query. This method effectively balances the load and enhances the performance and reliability of online services.
As we continue exploring the key components of networking in the cloud, our next article will dive into Load Balancing—a vital technique for distributing traffic across multiple servers to ensure high availability, reliability, and performance. Stay tuned!
The Genesis Cloud team 🚀
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