Watch Duty manages millions of requests per minute during California wildfires with the help of Fastly

The challenge

Watch Duty CEO and co-founder John Mills started the service to solve his own problem. Living off the grid in the woods of Northern California, he experienced first-hand the lack of accessible information about wildfires in his area. With the help of trained volunteers, including active and retired firefighters, dispatchers, and first responders, Watch Duty began reporting on fires in four California counties. Today, Watch Duty is available in 22 states, including Hawaii, and continuing to expand. In response, Watch Duty CTO and co-founder David Merritt is focused on building a bigger engineering operation and having the infrastructure resources in place to handle the growth in traffic.

The solution

Watch Duty talked with Fastly staff about the Fast Forward program, which provides free services to nonprofits and open-source projects. "As I started to look into what Fastly offered," Merrit said,"I realized how powerful these solutions could be, both from a compliance and WAF perspective and for a much more capable CDN." As a disaster-focused service, Watch Duty gets very spiky traffic, and it must deliver the most up-to-date information. "We want to cache everything, but have almost no tolerance for serving stale data," Merritt said. "We'd hit our limits on what we could do with some of the other CDN solutions, so we saw Fast Forward as an awesome opportunity."

Watch Duty had barely finished onboarding with Fastly before it was put to the test again. According to Merritt, "As it turns out, we were really lucky to have the VCL layer set up between our DNS and our backend prior to the breakout of the LA wildfires." During the month of January 2025, average monthly users skyrocketed to 10 million, traffic was 15 times what the service had experienced in the past, and Watch Duty was getting hit with up to 100,000 requests per second. "At that moment, " Merritt recalls, "we were very grateful to have a cache in front of all our backend services, because it would have definitely taken us down."

Handle historic traffic spikes with zero downtime

Given the massive population of Los Angeles, the Watch Duty team knew they were about to be hit with record-breaking traffic. Their first priority was to reduce traffic to their backend. "By implementing Fastly, we realized a huge reduction in traffic to our back end. We were at an 85% cache hit rate and over 60-70% of our traffic was cacheable," Merritt said. The scariest part for Watch Duty? "Los Angeles County mistakenly sent out an emergency alert to a much larger group than intended, which meant that everyone using Watch Duty in the LA area picked up their phones at exactly the same time. When we were at 100,000 requests per second and millions of requests per minute, we hit 15,000 to 20,000 requests a second to our backend, which is a lot, but nothing we hadn't handled before," said Merritt.

Watch Duty stayed available for users throughout the LA wildfires with zero outages and only one hour of slowdown. "We need 100% uptime," said CEO Mills. "People were relying on us in that time of crisis, and nothing else matters." To take action for their safety, users need content that loads fast but is absolutely up to date. "Our data is very cacheable, but it has to have very low time-to-live (TTLs) and very, very fast purges. That works perfectly with what Fastly offers," Mills said. ”We couldn't do this without Fastly as a huge part of our infrastructure."

Slashing scraper traffic with Fastly's Next-Gen WAF 

After the critical scaling for the LA wildfires, the Watch Duty team dug into the Next-Gen WAF functionality—and had some unexpected discoveries. "We started with the WAF integration for SOC 2 compliance—it was more of a must-do than a want-to-do," Mills said. “Once the WAF was in place, however, the value was obvious. Malicious actors were testing stolen credit card numbers through the app's donation form, and the team discovered that the service was being scraped by other people who wanted to use Watch Duty data for profit. Fastly's Next-Gen WAF was able to block those bad actors, so Watch Duty retains its content authority and high integrity.”

Moving to the edge for even better responsiveness

CTO Merritt said Watch Duty is looking forward to moving more of its logic to the edge. "We need to be able to modify content on the way out. Having a tool like Compute will make a lot of those application-level changes much simpler," he added. “Authorization, filtering and business logic for geospatial assets will all be enabled by using Compute. Watch Duty also plans to increase their use of Fastly's Object Storage, an S3-compatible storage solution for large objects that works with both the Fastly CDN and Compute.

Key takeaway

Watch Duty was created to meet a critical need that wasn't being addressed anywhere else, and it's quickly become an essential tool for communication during disasters. Likewise, Watch Duty came to Fastly for the scaling capacity, reliability, and caching infrastructure other services couldn’t provide. "Fastly helps us focus on what we're really good at: providing actionable disaster information," said Merritt. "Working with Fastly allows us to feel secure that we'll be reliable through those traffic spikes when the next major disaster hits."