Refresh relay auth tokens before they expire - #172
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Pull request overview
Updates the Azure Relay listener to proactively reconnect based on token expiry time, aiming to prevent daily production disconnects caused by Managed Identity token expiry.
Changes:
- Refactors
RelayListener.listen()into a reconnect loop that refreshes the connection when a timeout occurs. - Introduces
RelayURI.connection_details()to return both the connection URL and token expiry time (bearer/SAS). - Updates unit/integration test scaffolding to accommodate the new listen/connection flow and logging format.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| src/relay_listener.py | Adds token-expiry-aware connection lifecycle and URL/expiry retrieval via connection_details() |
| tests/test_relay_listener.py | Refactors tests to target _listen_on_connection() and verifies reconnect behavior and logging |
| tests/conftest.py | Updates fake_relay harness to align with the new listener behavior in integration-style tests |
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The relay connection token expires every 24 hours for MI tokens and has a predefined expiry for SAS tokens. By monitoring the time the connection has been open in an outer loop we can force the refresh of the token before it expires.
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| async with self._connect(connection_url) as websocket: | ||
| logger.info("Connected - waiting for worklist actions...") | ||
| await self._listen_on_connection(websocket, refresh_at) | ||
| except asyncio.TimeoutError: |
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I think this also catches an open-handshake timeout from self._connect() on line 86. Suggest a custom signal eg TokenRefreshDue(Exception) raised at line 97 and caught here. Relay connection failures then fall through to main()'s existing backoff.
carlosmartinez
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Jul 23, 2026
Distinguish between TimeoutError and a token expired event by raising a custom error.
carlosmartinez
approved these changes
Jul 28, 2026
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Description
Monitor the connection age of the Azure Relay Listener and refresh the credential token on the connection url before it times out.
This prevents daily disconnects in production, the Managed Identity token expiry is 24 hours.
Jira link
https://nhsd-jira.digital.nhs.uk/browse/DTOSS-13334
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