Originally published on the Merlonix blog.
Merlonix monitors uptime, SSL/TLS, DNS, email authentication, blacklists, Certificate Transparency, Core Web Vitals, and MCP servers for agencies. A monitoring product has an unforgiving shape: it must run continuously, hit arbitrary customer-supplied hostnames, and stay up more reliably than the things it watches — while, in our case, keeping the infrastructure bill within a rounding error of zero until revenue exists to justify more.
This post is the real architecture, including the parts that bit us. Nothing here is a reference design we aspire to; every component named below is deployed and verifiable from the outside.
The shape of the system
Compute: eight Cloudflare Workers. One HTTP API worker (Hono) serves everything under api.merlonix.com. Seven background workers do the actual monitoring: a scheduler (cron), a check-runner and vendor-runner (queue consumers that execute checks), a vendor-fetcher, a dlq-consumer (dead-letter forensics), a browser-runner, and a db-backup worker. Each has its own wrangler config and its own deploy verifier.
