envoyproxy/envoy

Non-hermetic DNS testing in eg dynamic_forward_proxy is causing recurring failure/slowness

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#42217 opened on Nov 24, 2025

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area/ciarea/dynamic_forward_proxyarea/test flakesbughelp wanted

Description

I stumbled upon this issue with the mobile test //test/common/integration:client_integration_test

in that case the test had a total timeout and was querying dns for doesnotexist - dns was retrying 3x, and taking 5+ seconds to respond on each try - blowing the tests total timeout budget

im struggling to find how i resolved the issue in mobile - but it seems i got past it

this problem has again occurred when trying to update the build image - asan and gcc are reliably timeouting on similar tests - and it looks like for similar reasons

i would have thought these tests should not be calling any real dns - it should be mocked and hermetic

Contributor guide

Tech stack
cpp
Domain
backendtestingperformance
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
C++ basicsUnderstanding of DNSFamiliarity with Envoy test framework
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Investigate the specific test `//test/common/integration:client integration test` and similar dynamic forward proxy tests to identify where real DNS queries are made. Look into mocking DNS responses using the test infrastructure, possibly by injecting a fake DNS resolver or using a simulated network. Examine any existing PRs or comments mentioning DNS mocking to understand prior attempts. The goal is to ensure all DNS queries in tests are hermetic and do not rely on external network calls.