Modestharbor
News and analysis from the world of production systems.
The Operator's Guide to Load Testing
July 1, 2026
Synthetic load generation consistently fails to replicate production outages because artificial traffic profiles lack real-world dynamics. Sending constant, uniformly spaced queries against a solitary URI tests that specific route in isolation. Real crashes stem from synchronized client retry spikes following a brief hiccup or morning crawler sweeps hitting unprimed caches.
Capturing and re-executing actual production traffic patterns—incorporating true endpoint ratios, user pauses, and diverse headers—delivers far more predictive value than inflating synthetic concurrency. Pay keen attention to packet arrival clustering: production traffic arrives in sharp surges rather than tidy Poisson curves, quickly swamping buffers.
Email Deliverability: Authentication Beyond SPF
August 8, 2026
SPF alone stopped being enough years ago. A message that passes SPF can still fail alignment, and mailbox providers have grown far more interested in DKIM signatures and DMARC policy than in the envelope any single check describes.…
Zero-Downtime Deployments Without the Drama
September 30, 2026
Popular engineering lore depicts seamless releases through elaborate blue-green switches and instantaneous traffic flips. Production reality centers on disciplined fundamentals: synthetic probes verifying realistic workloads, graceful connection draining on retiring nodes, and database schema mutati…
When to Choose a Queue Over a Request
September 2, 2026
Traditional RPC calls remain popular due to straightforward causality: the client makes an invocation, waits for the response, and monitors latency directly. Asynchronous message queuing becomes essential when background tasks outlast active connections or when sudden volume surges threaten to overw…
Practical Notes on Postgres Connection Pooling
August 29, 2026
Each incoming PostgreSQL connection instantiates an isolated operating system process with dedicated memory overhead, necessitating a dedicated pooling proxy in growing deployments. Classic session pooling acts transparently, whereas high-throughput transaction pooling frequently disrupts stateful f…
More reading
- Reading Latency Percentiles Without Fooling Yourself — Operations, July 1, 2026
- Structuring DNS for Reliability — Networking, September 9, 2026
- Multi-Region Failover Planning — Operations, August 5, 2026
About us
We cover the unglamorous middle of software: queues that back up, caches that lie, and DNS at 3 a.m. Everything is written from real operational experience.