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Eric EastwoodandGitHub
365df86536
Fix https://github.com/element-hq/synapse/issues/19907 The flake manifested as a failure pointing at `TestMessagesOverFederation/Backfill_from_nearby_backward_extremities_past_token` but was actually caused by some cross-test pollution from an earlier test (`TestOIDCProviderUnavailable`) causing some workers to be temporarily unavailable. As explained in https://github.com/element-hq/synapse/issues/19907#issuecomment-4917362461, > ### Cross-test pollution > > When I point an LLM at the logs, it points to `TestOIDCProviderUnavailable` being the culprit because of the server restarts polluting this test. When this flake happens, we can indeed see that `TestOIDCProviderUnavailable` runs before `TestMessagesOverFederation`. > > ``` > PASS TestEventBetweenMakeJoinAndSendJoinIsNotLost 15.08s > PASS TestFederation/parallel/HS2_->_HS1 1.5s > PASS TestFederation/parallel/HS1_->_HS2 1.51s > PASS TestFederation/parallel 0s > PASS TestFederation 15.12s > PASS TestOIDCProviderUnavailable//login/sso/redirect_shows_HTML_error 0.02s > PASS TestOIDCProviderUnavailable 8.62s > FAIL TestMessagesOverFederation/Backfill_from_nearby_backward_extremities_past_token 0.89s > FAIL TestMessagesOverFederation 1.1s > PASS TestSynapseVersion/Synapse_version_matches_current_git_checkout 0.97s > PASS TestSynapseVersion 0.97s > ``` > > The pollution happens because we enable [`COMPLEMENT_ENABLE_DIRTY_RUNS`](https://github.com/element-hq/synapse/blob/c63d77a79d7157f26f849684520ba9e99f4d07c0/scripts-dev/complement.sh#L309-L311) ([docs](https://github.com/matrix-org/complement/blob/0e6f8552ff0c99fddb97222399efed3e1f0cb91a/ENVIRONMENT.md#complement_enable_dirty_runs)) which means Complement will reuse deployments (shares homeservers between tests). > > During the `TestOIDCProviderUnavailable` test, there are some stray federation requests that hit the homeserver while it's still booting which marks the nginx upstream as unavailable for 10 seconds. nginx has a default of [`max_fails=1`](https://nginx.org/en/docs/http/ngx_http_upstream_module.html#max_fails) and [`fail_timeout=10s`](https://nginx.org/en/docs/http/ngx_http_upstream_module.html#fail_timeout). Then when `TestMessagesOverFederation` starts, we're still in the 10 second unavailable window and nginx doesn't even try to connect at all. > > <details> > <summary>LLM summary of the logs and how this happens in practice</summary> > > 1. **19:52:10–11** — the previous federation test finishes: `user-3:hs2` does a faster-join (`send_join?omit_members=true`) to `!YnyCRpCLIpimppIreR:hs1`, so `hs2` kicks off a `sync_partial_state_room` background resync that is still running when the test ends. > 2. **19:52:11.6** — `TestOIDCProviderUnavailable` starts and calls `deployment.StopServer(t, "hs1")` / `StartServer` (`complement/tests/oidc_test.go:78-80`) to apply an OIDC config fragment. `hs1` gets `SIGTERM`; new supervisord at 19:52:13.3. `hs2` is not restarted and keeps retrying its unfinished work. > 3. **19:52:14** — `hs1`'s nginx is up, but the Synapse workers aren't: `federation_inbound` only listens on `18015` at 19:52:18.7, `federation_reader` on `18016` at 19:52:19.0. > 4. **19:52:15–16** — `hs2`'s retries arrive in that gap: `PUT /_matrix/federation/v1/send/…` → `18015` refused; `GET /state_ids/!YnyCRpCLIpimppIreR:hs1` → `18016` refused. With nginx defaults (`max_fails=1`, `fail_timeout=10s`) and only one server per upstream block, both upstreams are now marked down until ~19:52:25/26. (Side casualty: `hs2`'s partial-state resync gives up — "We can't get valid state history" — and puts `hs1` on a 10-minute federation backoff.) > 5. **19:52:21.5** — the failing test's `make_join` for `@user-5-bob:hs2` reaches `hs1`'s nginx → `no live upstreams` → `502` → the join fails, even though the worker has been listening for 2.5 seconds by then. > 6. **19:52:22** — `TestSynapseVersion`'s `GET /_matrix/federation/v1/version` hits the same dead upstream → `502` → it fails too. > > So it's a flake caused by a race between the OIDC test's container restart, hs2's background federation retries, and nginx's passive health-check — not anything wrong with the backfill logic under test. > > </details> > > > We can indeed confirm this suspicion with these logs > > ❌ https://github.com/element-hq/synapse/actions/runs/28888070856/job/85701936736 (archive: [85701936736.log](https://github.com/user-attachments/files/29809986/85701936736.log)): > ``` > Error: 2026/07/07 19:52:20 [error] 34#34: *1 no live upstreams while connecting to upstream, client: 172.18.0.3, server: localhost, request: "PUT /_matrix/federation/v1/send/1783453927718 HTTP/1.1", upstream: "http://federation_inbound/_matrix/federation/v1/send/1783453927718", host: "hs1" > ... > > Error: 2026/07/07 19:52:21 [error] 33#33: *4 no live upstreams while connecting to upstream, client: 172.18.0.3, server: localhost, request: "GET /_matrix/federation/v1/make_join/%21scAbyTQDdaauGYicpU%3Ahs1/%40user-5-bob%3Ahs2?ver=1&ver=2&ver=3&ver=4&ver=5&ver=6&ver=7&ver=8&ver=9&ver=10&ver=11&ver=12&ver=org.matrix.msc3757.10&ver=org.matrix.msc3757.11&ver=org.matrix.hydra.11 HTTP/1.1", upstream: "http://federation_reader/_matrix/federation/v1/make_join/%21scAbyTQDdaauGYicpU%3Ahs1/%40user-5-bob%3Ahs2?ver=1&ver=2&ver=3&ver=4&ver=5&ver=6&ver=7&ver=8&ver=9&ver=10&ver=11&ver=12&ver=org.matrix.msc3757.10&ver=org.matrix.msc3757.11&ver=org.matrix.hydra.11", host: "hs1" > ``` > > The fix here would be to disable nginx's unavailable upstream behavior by configuring `max_fails=0` in the upstream block: https://github.com/element-hq/synapse/blob/c63d77a79d7157f26f849684520ba9e99f4d07c0/docker/configure_workers_and_start.py#L374-L378
.. image:: https://github.com/element-hq/synapse/raw/develop/docs/element_logo_white_bg.svg :height: 60px **Element Synapse - Matrix homeserver implementation** |support| |development| |documentation| |license| |pypi| |python| Synapse is an open source `Matrix <https://matrix.org>`__ homeserver implementation, written and maintained by `Element <https://element.io>`_. `Matrix <https://github.com/matrix-org>`__ is the open standard for secure and interoperable real-time communications. You can directly run and manage the source code in this repository, available under an AGPL license (or alternatively under a commercial license from Element). There is no support provided by Element unless you have a subscription from Element. 🚀 Getting started ================== This component is developed and maintained by `Element <https://element.io>`_. It gets shipped as part of the **Element Server Suite (ESS)** which provides the official means of deployment. ESS is a Matrix distribution from Element with focus on quality and ease of use. It ships a full Matrix stack tailored to the respective use case. There are three editions of ESS: - `ESS Community <https://github.com/element-hq/ess-helm>`_ - the free Matrix distribution from Element tailored to small-/mid-scale, non-commercial community use cases - `ESS Pro <https://element.io/server-suite>`_ - the commercial Matrix distribution from Element for professional use - `ESS TI-M <https://element.io/server-suite/ti-messenger>`_ - a special version of ESS Pro focused on the requirements of TI-Messenger Pro and ePA as specified by the German National Digital Health Agency Gematik 🛠️ Standalone installation and configuration ============================================ The Synapse documentation describes `options for installing Synapse standalone <https://element-hq.github.io/synapse/latest/setup/installation.html>`_. See below for more useful documentation links. - `Synapse configuration options <https://element-hq.github.io/synapse/latest/usage/configuration/config_documentation.html>`_ - `Synapse configuration for federation <https://element-hq.github.io/synapse/latest/federate.html>`_ - `Using a reverse proxy with Synapse <https://element-hq.github.io/synapse/latest/reverse_proxy.html>`_ - `Upgrading Synapse <https://element-hq.github.io/synapse/develop/upgrade.html>`_ 🎯 Troubleshooting and support ============================== 🚀 Professional support ----------------------- Enterprise quality support for Synapse including SLAs is available as part of an `Element Server Suite (ESS) <https://element.io/pricing>`_ subscription. If you are an existing ESS subscriber then you can raise a `support request <https://ems.element.io/support>`_ and access the `Element product documentation <https://docs.element.io>`_. 🤝 Community support -------------------- The `Admin FAQ <https://element-hq.github.io/synapse/latest/usage/administration/admin_faq.html>`_ includes tips on dealing with some common problems. For more details, see `Synapse's wider documentation <https://element-hq.github.io/synapse/latest/>`_. For additional support installing or managing Synapse, please ask in the community support room |room|_ (from a matrix.org account if necessary). We do not use GitHub issues for support requests, only for bug reports and feature requests. .. |room| replace:: ``#synapse:matrix.org`` .. _room: https://matrix.to/#/#synapse:matrix.org .. |docs| replace:: ``docs`` .. _docs: docs 🛠️ Development ============== We welcome contributions to Synapse from the community! The best place to get started is our `guide for contributors <https://element-hq.github.io/synapse/latest/development/contributing_guide.html>`_. This is part of our broader `documentation <https://element-hq.github.io/synapse/latest>`_, which includes information for Synapse developers as well as Synapse administrators. Developers might be particularly interested in: * `Synapse's database schema <https://element-hq.github.io/synapse/latest/development/database_schema.html>`_, * `notes on Synapse's implementation details <https://element-hq.github.io/synapse/latest/development/internal_documentation/index.html>`_, and * `how we use git <https://element-hq.github.io/synapse/latest/development/git.html>`_. Alongside all that, join our developer community on Matrix: `#synapse-dev:matrix.org <https://matrix.to/#/#synapse-dev:matrix.org>`_, featuring real humans! Copyright and Licensing ======================= | Copyright 2014–2017 OpenMarket Ltd | Copyright 2017 Vector Creations Ltd | Copyright 2017–2025 New Vector Ltd | Copyright 2025 Element Creations Ltd This software is dual-licensed by Element Creations Ltd (Element). It can be used either: (1) for free under the terms of the GNU Affero General Public License (as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version); OR (2) under the terms of a paid-for Element Commercial License agreement between you and Element (the terms of which may vary depending on what you and Element have agreed to). Unless required by applicable law or agreed to in writing, software distributed under the Licenses is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the Licenses for the specific language governing permissions and limitations under the Licenses. Please contact `licensing@element.io <mailto:licensing@element.io>`_ to purchase an Element commercial license for this software. .. |support| image:: https://img.shields.io/badge/matrix-community%20support-success :alt: (get community support in #synapse:matrix.org) :target: https://matrix.to/#/#synapse:matrix.org .. |development| image:: https://img.shields.io/matrix/synapse-dev:matrix.org?label=development&logo=matrix :alt: (discuss development on #synapse-dev:matrix.org) :target: https://matrix.to/#/#synapse-dev:matrix.org .. |documentation| image:: https://img.shields.io/badge/documentation-%E2%9C%93-success :alt: (Rendered documentation on GitHub Pages) :target: https://element-hq.github.io/synapse/latest/ .. |license| image:: https://img.shields.io/github/license/element-hq/synapse :alt: (check license in LICENSE file) :target: LICENSE .. |pypi| image:: https://img.shields.io/pypi/v/matrix-synapse :alt: (latest version released on PyPi) :target: https://pypi.org/project/matrix-synapse .. |python| image:: https://img.shields.io/pypi/pyversions/matrix-synapse :alt: (supported python versions) :target: https://pypi.org/project/matrix-synapse