Understanding DNS Failures: Separating Reality from Misconceptions

The Misattribution of DNS in Modern Internet Outages

In the digital age, the Domain Name System (DNS) is often blamed for a wide range of failures in software services. However, as Paul Tagliamonte pointed out in a recent post, this attribution may not always be accurate. He introduced an insightful rule: if you can replace the term ‘DNS’ with ‘a key-value store mapping a name to an IP’ and the issue still makes sense, then the failure was not truly DNS-related. This distinction sheds light on how complex systems often misrepresent their underlying issues, assigning blame to the DNS when the true culprit lies elsewhere in the infrastructure.

Jonathan Belotti further illustrated this phenomenon through his analysis of a recent outage in Amazon’s us-east-1 region. By interrogating the incident report, he showcased how some failures expose themselves as DNS-related, even though the root cause typically isn’t within the system itself. Belotti emphasized a critical approach to incident evaluation, highlighting the layered complexities and interdependencies that modern networks operate under.

Lessons from Systemic Failures and Architectural Design

Both Paul and Jonathan recognized a vital distinction between genuine DNS failures and those arising from broader design flaws or interconnection issues within a system. Belotti expanded on this by using the Swiss cheese model of system failure, initially developed by James Reason in the 1990s. According to this model, small errors in separate layers of a process can align to create significant disruptions — a scenario that is increasingly common in today’s interconnected software ecosystems.

One of the broader points raised is the importance of ‘dogfooding,’ a practice where organizations test their systems under real-world conditions using the same tools and services they provide to users. By relying on internally managed components, service providers can anticipate and mitigate potential failures more effectively. However, as demonstrated by the Amazon outage, even dogfooding has limitations when systems are tightly coupled and poorly understood at their points of integration.

Parallels Between Software Networks and Electricity Grids

Belotti also drew fascinating parallels between software networks and the operational challenges faced by electrical grids. Electricity networks must account for ‘black start conditions,’ where large-scale outages require small, self-sufficient devices to kickstart the entire system back into operation. Similarly, software networks must maintain mechanisms for manual intervention and the ability to restore systems to a known-good state. These fail-safes are crucial for ensuring service continuity during outages.

Ultimately, DNS often acts as a signal rather than a cause of failure, highlighting how different components of a system interact — and sometimes fail — to function cohesively. Engineers performing root cause analyses should examine how name-to-IP lookups interact with the broader system to reveal vulnerabilities and improve resilience.

Conclusions on DNS Misconceptions

The tendency to assign blame to DNS during outages reflects a broader misunderstanding of the complexities involved in modern system design. As Paul Tagliamonte and Jonathan Belotti have shown, misattributed failures can obscure the need for deeper insights into systemic interdependencies. By addressing these complexities head-on, organizations can build more robust, adaptable, and efficient networks, ensuring they are better prepared for future challenges.