At Slack, we recently undertook a significant shift in how we measure network performance: moving away from a third-party SaaS monitoring solution to an internally managed system of network probers. This transition wasn’t just a technical upgrade, it was a foundational change that enabled us to support modern protocols like HTTP/3. As we began rolling out HTTP/3 endpoints, we hit an unexpected blocker: we had zero visibility of our HTTP/3 traffic.
To bridge this gap, we contributed to the open-source community, making it possible for Prometheus users to monitor HTTP/3 traffic effectively for the first time. This work doesn’t just benefit Slack; it sets a precedent and provides tooling that any company can now adopt to gain visibility into their HTTP/3 performance without relying on external vendors.
This blog post details how Sebastian Feliciano, a Networking Foundations intern, significantly contributed to our efforts. He helped deploy our Prometheus Blackbox Exporter-based network monitoring solution across our infrastructure, and importantly, contributed HTTP/3 support to the Prometheus Blackbox Exporter.

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Slack engineering

Slack migrated from a third-party SaaS monitoring solution to an internally managed Prometheus-based network probing system. When rolling out HTTP/3 endpoints, they discovered a critical observability gap: no existing tools supported HTTP/3 (QUIC/UDP) probing. An intern, Sebastian Feliciano, implemented QUIC support for the Prometheus Blackbox Exporter using the quic-go library, contributed it upstream as an open-source PR, and also built an in-house solution to use the feature before the PR was merged. The result is a unified Grafana dashboard covering HTTP/1.1, HTTP/2, and HTTP/3 metrics, better alerting, and a community-available tool for HTTP/3 observability.

From Custom to Open: Scalable Network Probing and HTTP/3 Readiness with Prometheus