AggregateIntegrationTest.TwoClusters is flaky

[adisuissa]

The test AggregateIntegrationTest.TwoClusters defined in //test/extensions/clusters/aggregate:cluster_integration_test seems to be flaky.

Full error while running in Release x64 mode:

[ RUN      ] IpVersions/AggregateIntegrationTest.TwoClusters/0
[2025-02-19 20:19:22.301][2618][critical][assert] [test/integration/http_integration.cc:585] assert failure: 0. Details: Timed out waiting for new connection.
Error: 2-19 20:19:22.301][2618][error][envoy_bug] [./source/common/common/assert.h:38] stacktrace for envoy bug
Error: 2-19 20:19:22.304][2618][error][envoy_bug] [./source/common/common/assert.h:43] #0 Envoy::HttpIntegrationTest::waitForNextUpstreamRequest() [0xe65e77]
Error: 2-19 20:19:22.307][2618][error][envoy_bug] [./source/common/common/assert.h:43] #1 Envoy::HttpIntegrationTest::sendRequestAndWaitForResponse() [0xe659c5]
Error: 2-19 20:19:22.310][2618][error][envoy_bug] [./source/common/common/assert.h:43] #2 Envoy::HttpIntegrationTest::makeHeaderOnlyRequest() [0xe677a6]
Error: 2-19 20:19:22.313][2618][error][envoy_bug] [./source/common/common/assert.h:43] #3 Envoy::HttpIntegrationTest::testRouterHeaderOnlyRequestAndResponse() [0xe67855]
Error: 2-19 20:19:22.316][2618][error][envoy_bug] [./source/common/common/assert.h:43] #4 Envoy::(anonymous namespace)::AggregateIntegrationTest_TwoClusters_Test::TestBody() [0xcd41ed]
Error: 2-19 20:19:22.319][2618][error][envoy_bug] [./source/common/common/assert.h:43] #5 testing::internal::HandleExceptionsInMethodIfSupported<>() [0x23e3d8c]
Error: 2-19 20:19:22.322][2618][error][envoy_bug] [./source/common/common/assert.h:43] #6 testing::Test::Run() [0x23e3c4d]
Error: 2-19 20:19:22.325][2618][error][envoy_bug] [./source/common/common/assert.h:43] #7 testing::TestInfo::Run() [0x23e4f47]
Error: 2-19 20:19:22.327][2618][error][envoy_bug] [./source/common/common/assert.h:43] #8 testing::TestSuite::Run() [0x23e5dc9]
Error: 2-19 20:19:22.330][2618][error][envoy_bug] [./source/common/common/assert.h:43] #9 testing::internal::UnitTestImpl::RunAllTests() [0x23f3f7c]
Error: 2-19 20:19:22.333][2618][error][envoy_bug] [./source/common/common/assert.h:43] #10 testing::internal::HandleExceptionsInMethodIfSupported<>() [0x23f3a1c]
Error: 2-19 20:19:22.336][2618][error][envoy_bug] [./source/common/common/assert.h:43] #11 testing::UnitTest::Run() [0x23f389f]
Error: 2-19 20:19:22.338][2618][error][envoy_bug] [./source/common/common/assert.h:43] #12 Envoy::TestRunner::runTests() [0x1ce11f5]
Error: 2-19 20:19:22.341][2618][error][envoy_bug] [./source/common/common/assert.h:43] #13 main [0x1cdfbb0]
Error: 2-19 20:19:22.341][2618][error][envoy_bug] [./source/common/common/assert.h:43] #14 __libc_start_main [0x7f9ea8ceb083]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:129] Caught Aborted, suspect faulting address 0x6c00000a3a
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:113] Backtrace (use tools/stack_decode.py to get line numbers):
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:114] Envoy version: 0/1.34.0-dev/test/RELEASE/BoringSSL
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #0: __restore_rt [0x7f9ea8ecd420]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #1: Envoy::HttpIntegrationTest::waitForNextUpstreamRequest() [0xe65e77]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #2: Envoy::HttpIntegrationTest::sendRequestAndWaitForResponse() [0xe659c5]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #3: Envoy::HttpIntegrationTest::makeHeaderOnlyRequest() [0xe677a6]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #4: Envoy::HttpIntegrationTest::testRouterHeaderOnlyRequestAndResponse() [0xe67855]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #5: Envoy::(anonymous namespace)::AggregateIntegrationTest_TwoClusters_Test::TestBody() [0xcd41ed]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #6: testing::internal::HandleExceptionsInMethodIfSupported<>() [0x23e3d8c]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #7: testing::Test::Run() [0x23e3c4d]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #8: testing::TestInfo::Run() [0x23e4f47]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #9: testing::TestSuite::Run() [0x23e5dc9]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #10: testing::internal::UnitTestImpl::RunAllTests() [0x23f3f7c]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #11: testing::internal::HandleExceptionsInMethodIfSupported<>() [0x23f3a1c]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #12: testing::UnitTest::Run() [0x23f389f]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #13: Envoy::TestRunner::runTests() [0x1ce11f5]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #14: main [0x1cdfbb0]
[2025-02-19 20:19:22.341][2618][critical][backtrace] [./source/server/backtrace.h:121] #15: __libc_start_main [0x7f9ea8ceb083]
Execution result: https://mordenite.cluster.engflow.com/actions/executions/ChCgHfMQ0UNCiqLjEC0JFA-PEgdkZWZhdWx0GiUKID19DuzccH2l-zctgEQdcYGl_-4xRRH6mqnvW1lgRFEnEKgD

Full error link: https://github.com/envoyproxy/envoy/actions/runs/13421390934/job/37494661486#step:17:1169

Might be related to #38253 but occurs in a different test, so I'm opening a new tracking ticket.
cc @alyssawilk