I have a good understanding of how DNS works, including how DNS names are resolved and the role of NS servers. However, one aspect is unclear to me: if we purchase a domain name and it resolves to its NS server, why is it necessary to also buy DNS hosting on a service like Cloudflare and register NS there?
what happens if the native NS server for our domain experiences a failure while a client is executing a DNS query? In this scenario, the root DNS server will respond by issuing the address of the NS server responsible for that zone (i.e. the native NS), but if that server has failed, what will happen? Specifically, will the root DNS server instead issue the address of the Cloudflare hosting NS server, even though it is not native to the domain we purchased? This raises an interesting question about DNS redundancy and backups.
To ensure the support of any DNS zone, it is customary to have a minimum of two DNS servers that handle this zone. When zone management is delegated to these servers, no other entity can respond to requests for DNS records within this zone. Additionally, at higher-level DNS servers, there will only be records pertaining to the delegation of your zone and nothing more.
I apologize for the previous unstructured and difficult-to-read text. It is important to ensure that technical information is communicated clearly and effectively. Do you have any further questions about DNS management or best practices?
It is important to note that domain registrars are not required to provide DNS hosting as part of their services. In fact, many registrars do not offer DNS hosting, which means that you must provide your own NS servers in order for your domain to function properly, or the registrar may not allow you to purchase the domain at all.
As the owner of a zone, you have the responsibility of setting up your own NS servers to manage the settings for all the domains within that zone. When registering your domain with a registrar, you must specify the NS servers you are using for that zone. If the registrar does provide DNS hosting services, they will simply register their own NS servers in the zone settings.
It's important to choose a reliable DNS hosting provider to ensure that your website remains accessible at all times. Additionally, regularly verifying and updating your DNS records can help prevent potential issues and downtime.
Before delving into DNS servers, let's discuss the technology that underpins them: the Domain Name System (DNS). DNS facilitates the process of locating websites by their names, allowing browsers like Firefox, Chrome, and Edge to connect users with their requested sites.
The way DNS functions can be compared to utilizing a phone book in order to make calls. Just as a phone book provides a name and number, DNS provides a site name and its corresponding IP address in the format xхx.xхx.xхx.xхx. Each octet of the IP address occupies a single byte within the range of 0 to 255. When a user types a site name into a browser address bar, such as google.com, their computer requests this site's IP address from a DNS server, which it then uses to open the site.
A DNS server serves as the "contact book" of the internet, storing IP addresses for sites alongside domain information and providing this data to users upon request. The caching of DNS records of other servers further streamlines this process. While the root DNS servers represent exceptions, as they store all necessary DNS information, local DNS servers usually interact with other regional DNS servers to obtain needed data before sending it to the user's computer.
When a user navigates to a website, their local DNS server checks its hosts file to determine if the site's IP address has already been cached. If not, the request is sent onwards to the user's ISP's local DNS server, which then engages with other DNS servers until it acquires the necessary information. Cached information is stored for future use, although this information will eventually expire according to server settings.
If a site switches servers or hosting providers, its IP address will change accordingly. In such situations, requests are initially processed in the old way, redirecting users to the old IP address. After a certain period of time, typically a day, the cache of the local DNS servers is updated with the new IP address, thereby ensuring user access to the site is directed toward the correct IP address.
When you register a domain, you are essentially purchasing the rights to use a unique address on the internet. The domain registrar company, where you purchased the domain, usually provides DNS servers that can hold records for your domain, pointing to your website, email server, etc. This is the "native" setup you're referring to.
DNS hosting like Cloudflare provides additional functionality and reliability beyond what typical domain registrars might provide. This includes features like DDoS protection, faster DNS resolution, load balancing, easy SSL/TLS setup, and much more.
When you configure Cloudflare (or any other DNS hosting service) for your domain, you are instructed to change the nameserver (NS) records at your domain registrar to point to Cloudflare's nameservers. Once you've made this change, Cloudflare's nameservers become authoritative for your domain. This means, when a DNS query happens for your domain, the DNS resolution path will lead to Cloudflare's DNS servers.
Now to your question about failures and backups. If your authoritative DNS server (let's say Cloudflare's) experiences a failure while a client is executing a DNS query, the failure will likely cause trouble for that client query. The query would most likely fail, unless the client DNS resolver has a cached version of the domain's DNS data. The root DNS server is not going to redirect the query to your domain registrar's nameservers because from the perspective of the global DNS system, Cloudflare's servers are the authoritative source for your domain.
To achieve redundancy and maintain uptime in the face of server failures, DNS hosting providers like Cloudflare use multiple DNS servers distributed around the world. So if one server fails, another one can serve the DNS records. This distributed architecture makes the DNS system resilient to regional outages, traffic congestion, and server failures.
As for DNS backups, many DNS services, including Cloudflare, keep copies of your DNS records on multiple servers. It makes it highly unlikely that all copies would be lost at the same time. However, it's a good practice to keep your own backup of your DNS records.
If you're interested in high availability and DNS failures, one method to ensure high uptime is to use multiple DNS providers. For example, you could use both Cloudflare and another DNS hosting company. To do this, you would configure DNS at both providers to be the same, and set your domain to use nameservers from both companies.
In this dual hosting setup, both DNS providers have the same, mirrored records. When a user wants to reach your site, the query goes to the root servers and then to either provider, depending on the client's location, network conditions, etc. If one provider goes down, the other is still available to respond to DNS requests. This method requires more configuration and upkeep but provides better redundancy.
Now, if you also want to understand the kind of impact a failure could have, it's important to discuss DNS TTL or "Time To Live". TTL is a value in a DNS record that tells how long that information should be cached by DNS resolvers or clients. For example, if a DNS record has a TTL of 1 hour, then a DNS resolver will use its cached data to answer queries for that domain for the next hour, instead of going back to the authoritative DNS server. After the TTL expires, the resolver will discard the cached data and fetch the fresh data from the authoritative server.
So, even if a DNS server fails, if the TTL for your DNS record hasn't expired, the DNS resolver can still provide the cached information. So brief failures might not cause noticeable problems for end users. However, long TTLs could also delay updates to DNS records from being noticed.
It's also important to note that even with the best DNS hosting setup, your website's availability also depends on the reliability and redundancy of your web or application servers. Those servers should also be designed for high availability, using techniques like load balancing, auto-scaling, geo-redundancy, etc., to prevent a single point of failure.
Continuity in internet services is about risk management. It requires a balance between resources spent and the level of reliability desired. Full-proof redundancy is rare and expensive - the more "nines" of reliability you want (e.g., 99.999% uptime), the more it costs. But with the right setup, you can make your site highly resilient to outages.
let's delve even more into the intricacies of DNS.
Another key aspect to mention is Anycast networking which is commonly used by DNS providers like Cloudflare. Anycast is a network addressing method that allows one IP address to be associated with multiple different physical locations or servers. When your DNS is set up with an Anycast provider, it allows your DNS queries to be answered from the geographically closest location among the multiple configured servers.
Think of it this way: you have identical information stores (DNS records) in multiple cities and a system for routing a request (DNS query) to the nearest location. This kind of distribution not only helps to reduce latency, leading to faster responses, but also offers inherent fail-over capability. In case of a failure in one location, the network routers can detect this and automatically redirect traffic to the next closest location still up and running. It's a built-in dynamic backup solution at the network level.
Let's also talk about DNSSEC (Domain Name System Security Extensions). While DNSSEC doesn't directly contribute to the redundancy or backup of your DNS system, it enhances the security of your DNS setup by countering DNS cache poisoning attacks. It accomplishes this by authenticating the origin of DNS data and ensuring data integrity from the server to the client. In an era where security is paramount, adding DNSSEC might be worth considering, but it does add complexity to your DNS setup and is not universally supported.
In relation to NS records, you usually have at least two for redundancy. The additional NS records act as backups if the primary NS server fails. Mind you, all these should point to different physical servers to provide true redundancy.
Finally, it's worth noting that the implementation of DNS redundancy can be as simple or as complex as you need it to be, depending on the requirements of your organization or the particular application.
While smaller websites typically don't need multiple DNS providers, for larger applications with worldwide audiences, multiple DNS providers in concert with Anycast networking and other redundancy measures may be the best way to ensure high availability and performance. Still, it's a balancing act between cost, complexity, performance, and availability. It's critical to understand your needs and risks to decide which measures are appropriate for your situation.