A Better Way to a Redundant DNS.

Transcription

1 WHITEPAPE R A Better Way to a Redundant DNS GET.NSONE (6766) NS1.COM

2 Executive Summary DNS is a mission critical application for every online business. In the words of Gartner If external DNS fails, so does your digital business. While there is a great deal of resiliency built into the architectures of top tier DNS providers, they are a single point of failure in the infrastructure of enterprises that rely solely on one provider. DNS redundancy is well recognized as a best practice for online enterprises. It is a fact however that most enterprises have not adopted a redundant DNS strategy. A 2018 study from Thousand Eyes revealed that 68% of Fortune 50 companies are relying on a single DNS provider. The study did show a significantly higher adoption rate of dual provider DNS amongst major SaaS companies who are often more leading edge in their technological approaches. The low adoption rate of redundant DNS appears to be due to the following: 1. The risks and consequences of DNS outages are not well understood. 2. There is lack of knowledge on the best strategies for implementing redundant DNS This white paper provides information on these issues. The paper covers reasons why DNS systems fail and approaches for balancing the cost benefit trade-offs of implementing a redundant DNS strategy. The paper explains the technical considerations and trade-offs of different approaches to implementing redundant DNS and how to evaluate which approaches are best for your business. NS1 has helped many enterprises implement redundant DNS in conjunction with other DNS providers, in conjunction with in house/self-hosted DNS systems and with a unique solution from NS1 called Dedicated DNS. This white paper will help IT managers and architects make a better, informed decision regarding whether and how to implement a redundant DNS strategy GET.NSONE (6766) NS1.COM WHITEPAPER 2

3 Managed DNS Architectures A robust managed DNS has to be highly available and high performing. The foundational elements for achieving this are: Multiple points of presence, with strong global geographic coverage Globally anycasted Well provisioned (servers, storage, bandwidth) Uses top tier network connectivity, IXP and colocation providers Overprovisioned to absorb traffic spikes and DDoS attacks Round the clock monitoring and incident response The value of a DNS system architected and run by experts is not to be underestimated. Few enterprises have the technical depth and resources to do this really well. Single Point of Failure Top tier managed DNS systems have a great deal of built in redundancy and fault tolerance, but all managed DNS providers have experienced problems to some degree with resulting impact on their customers. While rare, providers can even experience a complete loss of service. In short, no system is failure proof, so from the point of view of a subscribing enterprise, their managed DNS does represent a single point of failure. It is often the case that only after they have experienced a loss of DNS service from their provider that enterprises decide to bring on a second provider. A proactive approach is clearly better. The question every enterprise should address is whether bringing in a second DNS service is worth the effort and cost. Managed DNS providers do publish availability statistics and the industry norm exceeds 5 nines (99.999% uptime) about 5 minutes per year downtime. However, this top line number does not provide the detail needed to properly assess the business risk associated with relying on a sole source provider. It is not clear for example what the probabilities and impact are of degraded performance in certain regions or probabilities of a system wide outages of various duration. What enterprises can do is look at the issue from the perspective of their business. What would a 30-minute loss of DNS cost the business in terms of revenue, reputation damage, support costs and recovery? Compare that with the cost of a second source DNS. Enterprises that are highly dependent on their online presence will generally conclude that the cost ratios are in the range of at least 10:1 one order of magnitude. Put another way, the cost of one DNS outage is likely to be at least ten times the annual cost of a second service. That would put the breakeven point at about 1 major DNS outage every 10 years GET.NSONE (6766) NS1.COM WHITEPAPER 3

4 The Basics of DNS Redundancy Understanding the basics of redundant DNS starts with understanding the basics of DNS itself. The subscribing customer hosts their DNS zones on the providers name servers. The name servers are registered with the top level domain (TLD) as authoritative for the zones of the subscribing customer. Managed DNS providers typically provide a list of four authoritative servers that the subscribing customer can list in the delegation. These four name servers actually represent many physical servers hosted in multiple data centers around the world. That is a reason why managed DNS services are generally reliable and performant. When a DNS resolver receives a query, the resolver queries the top level domain (TLD) to get the list of authoritative name servers for the desired zone. It receives that list of four and selects one of the name servers in the list to query for the record. If it receives no reply it will retry. If again no reply is received it will choose another name server in the list. So what can go wrong? The four name servers each have a unique IP address which is anycasted to all the points of presence where the physical servers are hosted. So if a POP in a particular region goes down, users in that region will experience a period of slowdown due to timeouts, retry delays, and traffic routing adjustments to send queries to a different POP. Second, traffic spikes in combination with problems at specific POPS can cause problems to propagate across the system with high rates of retransmit requests adding to loads system wide. Managed services are typically shared. So the effects of DNS DDoS attacks aimed at one customer on the system can affect other customers so called collateral damage. In short, although the architecture of better DNS managed services is highly distributed, these services are designed to work as a single system. To achieve a redundant DNS you need two sets of DNS name servers in the delegation that are hosted independently. That means they don t share the same colocation facilities, network connectivity or anycasted network. Redundant DNS and Secondary DNS Not the Same Thing Secondary DNS is one way to achieve redundant DNS but it is not the same as redundant DNS. A primary DNS server (sometimes referred to as a master DNS server) is the source of DNS information - the zones and records. DNS administrators make changes to the zone files on the primary DNS server and those changes are propagated from the primary DNS server to all the secondary DNS servers. Primary secondary configuration is a means of managing updates to multiple servers but does not provide redundancy. For example, many enterprises set up a hidden master (a primary DNS server that does not answer queries) and use it to send DNS changes to their managed DNS provider. The managed DNS in this case is a secondary DNS in a single provider set up GET.NSONE (6766) NS1.COM WHITEPAPER 4

5 Methods for Achieving Redundant DNS Achieving a redundant DNS means having two (or more) independent DNS networks actively answering queries. If one of those networks fail, the other will seamlessly and automatically pick up the slack. It is worth pointing out that both DNS networks must be active for redundancy to work. The reason is the time it takes to bring a DNS network online. A registrar needs to be contacted to add the name servers to the delegation. Otherwise the top level domain servers have no knowledge of them. This process can take 24 hours or more. For redundancy to work, the nameservers for both DNS networks must be registered with the TLD. Redundant DNS with two DNS providers can be achieved in different ways: 1. One provider is primary, and the other is secondary. The secondary provider receives zone updates from the primary. Enterprise IT personnel enter any DNS changes on the primary provider system, and have a zone transfer mechanism (typically NOTIFY and AXFR) set up between the two providers. 2. The other method is having both providers function as primary. In this mode there is no communication between the systems. The DNS administrator needs to enter zone updates on each system, separately. 3. A third option is the enterprise hosts a hidden master DNS and sets up both providers as secondary to the hidden master. These methods have advantages and disadvantages which relate to how the DNS is used. Modern DNS systems have built in traffic steering capabilities that perform functions such as active failover, geo routing and custom weighted load balancing. These functions are implemented using meta data that are associated with the DNS records but are not part of the records themselves. As a result, the standard zone transfer protocol (AXFR) that is used to synchronize records from primary to secondary DNS does not transfer that meta data. There are also no standards for the meta data and each DNS vendor implements DNS traffic management in their own way. Dual provider primary secondary DNS configurations do not support DNS traffic management. To maintain the benefits of DNS traffic management and have a dual provider DNS the records on both systems must be managed and updated separately. This can be done manually through the GUI or CLI interfaces to both systems, or through APIs. Automation using APIs can provide a single interface for the DNS domain administrator to update the records in both systems. This becomes progressively more complex if the middleware needs to support the more advanced routing features. It is generally left up to the customer to develop this middleware but some dual provider middleware implementations have been made generally available. Typically these are limited in functionality and not necessarily maintained GET.NSONE (6766) NS1.COM WHITEPAPER 5

6 The advantages and disadvantages of these approaches are summarize in Table 1 below. Method Advantages Disadvantages Dual Provider, Primary/Secondary Automated record synchronization No support for DNS traffic management Both providers must support zone transfer protocols Double the management overhead Dual Provider Primary/Primary DNS traffic management is supported Greater possibility of admin errors Differences in DNS traffic management features and capabilities can cause problems Table 1: Advantages and disadvantages of dual provider set ups. These issues highlight the need for a better alternative, one that is easy to manage and does not impose limitations on DNS traffic management GET.NSONE (6766) NS1.COM WHITEPAPER 6

7 NS1 Dedicated DNS: A Unique and Better Redundant DNS Solution NS1 s Managed DNS can be implemented in conjunction with another managed DNS service, or in conjunction with an enterprise self hosted DNS. NS1 supports the suite of zone transfer protocols (AXFR, IXFR, NOTIFY, TSIG) and can function as a secondary or primary DNS in a dual provider set-up. NS1 APIs are comprehensive and easy to use so record management can be automated. However, as noted above, the standard dual provider methods for achieving redundant DNS all leave something to be desired. They involve accepting trade-offs in functionality, manageability or both. NS1 has developed a solution that solves the complications and limitations of other approaches. NS1 Dedicated DNS is a fully managed DNS service, just like NS1 s Managed DNS. The difference is NS1 Dedicated DNS is not a shared service. It is a single tenant DNS solution deployed on physically separate infrastructure (servers, network connectivity) from Managed DNS. Every Dedicated DNS deployment is designed, deployed and managed by NS1 to meet the traffic load and distribution requirements of the subscribing enterprise. Dedicated DNS is managed using the same interface as Managed DNS. Whether the subscribing enterprise uses the NS1 APIs or the management GUI, record management is a one step, one place process with single pane of glass view into all records and reporting. There is no way for records to drift out of synchronization and all updates are reflected virtually simultaneously across all servers, within seconds. All traffic management features are supported. NS1 Managed DNS in conjunction with Dedicated DNS provides the redundancy of a dual provider solution with none of the complications of record synchronization, zone transfers and traffic management. It also is much more straightforward to implement from the customer perspective. NS1 sets up the Dedicated DNS network, which appears as an additional DNS network in their NS1 portal account (Figure 1). Adding zones and records to Dedicated DNS is a simple matter of checking a box to attach existing or new zones to the Dedicated DNS network. There is no need to set up a contract with another DNS provider or configure, test and monitor that records are correctly managed and synchronized on both systems. It all just works GET.NSONE (6766) NS1.COM WHITEPAPER 7

8 Figure 1. Single management interface for Managed and Dedicated DNS Dedicated DNS is a unique solution in the industry to the complexity and trade-offs that come with implementing a redundant DNS architecture. It simplifies management, reduces the risk of errors and provides that key level of availability assurance needed by online enterprises. ABOUT NS1 NS1 is the leader in next generation DNS solutions that orchestrate the delivery ABOUT NS1 of the world s most critical internet and enterprise applications. Only NS1 s NS1 is the leader in next generation DNS solutions that orchestrate the delivery of purpose-built platform, which is built on a modern API-first architecture, the world s most critical internet and enterprise applications. Only NS1 s purposebuilt platform, transforms which DNS into is built an intelligent, on a modern efficient API-first and automated architecture, system, transforms driving DNS into an intelligent, dramatic efficient gains in reliability, and automated resiliency, system, security driving and performance dramatic gains of application in reliability, resiliency, delivery security infrastructure. and performance Many of the of highest-trafficked application delivery sites infrastructure. and largest global Many of the highest-trafficked sites and largest global enterprises trust NS1, including Salesforce, enterprises trust NS1, including Salesforce, LinkedIn, Dropbox, Nielsen, LinkedIn, Dropbox, Nielsen, Squarespace, Pandora and The Guardian. Squarespace, Pandora and The Guardian GET.NSONE (6766) NS1.COM WHITEPAPER 8