datadog Failure is inevitable: Learning from a large outage, and building for reliability in depth at Datadog | Datadog (opens in new tab)
Following a major 2023 incident that caused a near-total platform outage despite partial infrastructure availability, Datadog shifted its engineering philosophy from "never-fail" architectures to a model of graceful degradation. The company identified that prioritizing absolute data correctness during systemic stress created "square-wave" failures, where the entire platform appeared down if even a portion of data was missing. By moving toward a "fail better" mindset, Datadog now focuses on maintaining core functionality and data persistence even when underlying infrastructure is compromised. ## Limitations of the Never-Fail Approach * Classical root-cause analysis focused on a legacy, unsupervised global update mechanism that disconnected 50–60% of production Kubernetes nodes. * While the "precipitating event" was easily identified and disabled, the engineering team realized that fixing the trigger did not address the systemic fragility that caused a binary (up/down) failure pattern. * Prioritizing absolute accuracy meant that systems would wait for all data tags to process before displaying results; under stress, this caused the UI to show no data at all rather than "almost correct" data. * Sequential queuing, aggressive retry logic, and node-specific processing requirements exacerbated the bottleneck, preventing real-time recovery. ## Prioritizing Graceful Degradation * The incident prompted a shift away from relying solely on redundancy to prevent outages, acknowledging that some level of failure is eventually inevitable at scale. * Engineering priorities were redefined to ensure that data is never lost (even if delayed) and that real-time data is processed before stale backlogs. * The platform now aims to serve partial-but-accurate results to customers during an incident, providing visibility rather than a complete blackout. * Implementation is handled as a company-wide program where individual product teams adapt these principles to their specific architectural needs. ## Strengthening Data Persistence at Intake * Analysis revealed that data was lost during the outage because it was stored in memory or on local disks before being replicated to persistent stores. * The original design favored low-latency responses by acknowledging receipt of data before it was fully replicated, making that data unrecoverable if the node failed. * Downstream failures caused intake nodes to overflow their local buffers, leading to data loss even on nodes that remained online. * New architectural changes focus on implementing disk-based persistence at the very beginning of the processing pipeline to ensure data survives node restarts and downstream congestion. To build truly resilient systems, engineering teams must move beyond trying to prevent every possible failure trigger. Instead, focus on designing services that can survive partial infrastructure loss by prioritizing data persistence and allowing for degraded states that still provide value to the end user.
