Systems | Development | Analytics | API | Testing

Somewhere in your service is a branch that has never executed. Not a rare one, a never one. It handles a dependency being unavailable: it reads from a cache, it returns a stale value, it marks the response degraded so callers know not to trust it too far. It was written carefully. It was reviewed. Whether it works is an open question, because nothing in the test suite makes that dependency fail, and the dependency does not fail on request.

Scoped chaos rules are now in proxymock. A filter query picks the traffic, an effect perturbs it, and every response that gets touched is labelled so you can tell an injected failure from a real one for the rest of the run. Available in v2.5.892 and newer. The short version of why: kill a pod and you learn something real, but you do not learn what your service does when a dependency stays up and starts lying to it.

An engineering leader asked me a question a few weeks ago: could we read their business workflows out of API traffic instead of asking people to document them? I said it should be possible. Then I tried it. A few engineers know how the system really works. They know which calls make up a work order and which checks happen after a write. That stuff rarely makes it into the test plan. Usually it’s in somebody’s head. Sometimes it’s in several heads, with slightly different answers.

Self-hosting OTA updates became common after App Center and CodePush shut down in 2025. CodePush had been the popular free option, but the remaining hosted services easily hitting five or six figure bills for popular apps. For staging-only or use with small user bases, self-hosting is fairly straight forwards. But, as the user base grows, the architecture can start to struggle and bolt on pieces are required.

Engineering leaders have been claiming to “shift quality left” for years but production remains stubbornly stuck out of reach of software engineers. The realm of production remains mysterious with tools no one has access to and UIs that wouldn’t make sense to engineers anyway. I’ve noticed a small but growing trend of large enterprises hiring Reliability Engineers instead of Site Reliability Engineers. Dropping one word looks cosmetic but I think it points to a much bigger change.

A metric says latency increased. A log says a request failed. A trace identifies the slow dependency. An APM agent points to the method. Manual instrumentation explains the business operation. Traffic capture shows the exact request and response that triggered it. Each layer answers a question the previous layer could not. Each also introduces a new cost, blind spot, and failure mode.

React Native OTA tools in 2026 split across two clients, Expo Updates and CodePush-style, and two ways of running them, hosted or self-hosted. The clients are not interchangeable. You still need the matching SDK.

We shipped a chaos feature that never caused any chaos. Our mock server has had a fault-injection effect for years with a straightforward job: withhold the response entirely and see whether the caller copes. Last week I audited it against the actual code path. It had never withheld anything. The handler returned early without writing a response. Go’s net/http then did what it is designed to do, which is synthesize a 200 OK and flush the recorded body.