--- title: "How To Get Started With Chaos Testing Using mirrord" url: https://daily.dev/posts/how-to-get-started-with-chaos-testing-using-mirrord-hehtl0qjo source_url: https://metalbear.com/blog/chaos-testing-mirrord type: article source: "MetalBear" published: 2026-08-25T07:44:03.976Z updated: 2026-08-25T07:44:35.835Z tags: ["testing", "kubernetes"] reading_time: 11 upvotes: 1 comments: 0 language: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # How To Get Started With Chaos Testing Using mirrord **[MetalBear](https://daily.dev/sources/metalbear)** · 11 min read · 1 upvotes · 0 comments ## Summary A hands-on walkthrough shows how to use mirrord's chaos testing feature to inject latency and connection errors into a single developer's session against a shared staging cluster, without affecting anyone else on the cluster. Using a small loan-application demo app with two outgoing calls (one with a timeout and retry, one without), the guide demonstrates how faults like injected latency, connection resets, and partial (percentage-based) faults expose a missing timeout bug in one service. It then shows fixing the bug (adding a timeout and a manual-review fallback for unknown fraud risk) while the fault stays applied, and shows how faults can be moved one hop deeper onto a dependency's own dependency (e.g., a Postgres call). Requires mirrord 3.250.0 or newer. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How do I use mirrord to test what happens when a dependency service goes down or gets slow, without affecting other developers on the shared cluster? mirrord chaos scopes fault injection to a single session, so you add a rule (via mirrord chaos add -s $SESSION_ID -f rule.json) targeting an upstream selector, and only requests carrying your session's baggage header hit the fault. Effects include latency (read_ms/write_ms) and connection_error (e.g., reset), with a percentage field to apply the fault to only some connections. Requires mirrord 3.250.0 or newer. _See how daily.dev surfaces practical walkthroughs like this for evaluating chaos testing tools._ ### What is the difference between adding a timeout to an outgoing fetch call and leaving it unbounded, in terms of how the app behaves when a dependency hangs? An unbounded fetch (no AbortSignal.timeout) waits as long as the fault or dependency takes, in one demonstrated case 40 seconds, with no fallback behavior. Adding AbortSignal.timeout with a bound (e.g., 2 seconds) plus a defined fallback (reporting risk as 'unknown' and routing to manual review) means requests abort at the bound and retry, turning a multi-second hang into a bounded, predictable outcome around 2-4 seconds. _Developers hardening service timeouts can track patterns like this on daily.dev before shipping._ ### Why does an intermittent fault affecting only 30% of requests to a dependency sometimes pass a smoke test even though the service has a real reliability bug? Because most requests through a partial fault succeed by chance, a smoke test with only a few requests is likely to see all-passing results even when roughly a third of connections would hit multi-second latency. In one demonstrated run, 12 sequential requests to a fraud-check dependency with 30% latency injection showed 4 out of 12 hanging for 5-8 seconds, a pattern a single smoke test could easily miss. _daily.dev helps engineers stay on top of testing techniques that catch intermittent failures early._ ## Similar posts on daily.dev - [Introducing mirrord Chaos Testing](https://daily.dev/posts/introducing-mirrord-chaos-testing-emvolloz5) · MetalBear · 24 upvotes · 2 comments - [How To Prevent Token Burn Using mirrord With E2E Tests](https://daily.dev/posts/how-to-prevent-token-burn-using-mirrord-with-e2e-tests-9rav0oih4) · MetalBear · 1 upvotes · 0 comments --- Tags: [#testing](https://daily.dev/tags/testing), [#kubernetes](https://daily.dev/tags/kubernetes) [View this post on daily.dev](https://daily.dev/posts/how-to-get-started-with-chaos-testing-using-mirrord-hehtl0qjo)