Downdetector's Cloudflare Dependency: The Pragmatic Cost of Uptime Monitoring

The November 2025 Cloudflare outage highlighted a crucial dependency for Downdetector, a real-time outage monitoring service, which itself experienced downtime. This might initially seem counterintuitive, given Downdetector's mission to monitor system uptimes. However, the situation reveals a pragmatic approach to infrastructure dependencies.

Downdetector was engineered for multi-region and multi-cloud resilience, a design choice confirmed by Dhruv Arora, Senior Director of Engineering at Ookla (the company behind Downdetector). This multi-cloud strategy is particularly vital for Downdetector, as it needs to detect outages across various cloud providers, necessitating a diversified infrastructure.

Despite its multi-cloud setup, Downdetector relies on Cloudflare for critical services like DNS, Content Delivery Network (CDN), and Bot Protection. This dependency is justified by several significant advantages offered by CDNs:

• Reduced Bandwidth Costs: Assets cached on a CDN are served much faster, leading to lower bandwidth expenses.
• Improved Load Times: CDN edge nodes, located closer to users, ensure quicker content delivery.
• Traffic Spike Protection: CDNs absorb sudden surges in traffic, common for Downdetector during major outages, preventing service overload.
• DDoS Protection: Robust defenses against distributed denial-of-service attacks safeguard the site from malicious actors.
• Lower Infrastructure Requirements: Leveraging a CDN allows Downdetector to operate efficiently with fewer internal servers.

Downdetector's business model, which primarily serves consumers with a free service, strongly influences these infrastructure decisions. While removing Cloudflare as an upstream dependency is technically feasible, it would lead to a substantial increase in operational costs and slower site performance without a corresponding rise in revenue.

Arora elaborated on Downdetector's design philosophy: "Building redundancy at the DNS & CDN layers would require enormous overhead. This is especially true as Cloudflare’s Bot Protection is world-class, and building similar functionality would be a lot of effort." He further noted that while hyperscalers offer built-in redundancy, developing such core infrastructure internally is a significant challenge for a mid-sized team.

The outage also provided valuable lessons for future improvements. Arora mentioned that during the incident, Cloudflare's control plane was down, but its API remained operational. This suggests that a more robust Infrastructure-as-Code implementation could have accelerated Downdetector's recovery. Furthermore, the team observed that the outage was not global, allowing them to redirect traffic and mitigate impact. A peculiar detail was Cloudflare's Bot Protection system malfunctioning and blocking legitimate traffic, necessitating its temporary deactivation by Downdetector's team.

This incident underscores the complex trade-offs involved in managing upstream dependencies, even for services designed for high availability and outage detection.