241 lines
6.9 KiB
Python
241 lines
6.9 KiB
Python
"""Supervision: a background task that dies gets restarted, until it is hopeless."""
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import asyncio
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import pytest
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from fluksio.flow import supervision
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from fluksio.flow.events import EventBus
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from fluksio.flow.supervision import FAILURE_BUDGET, QUARANTINE_BACKOFF, Supervisor
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@pytest.fixture(autouse=True)
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def no_backoff(monkeypatch: pytest.MonkeyPatch):
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"""Real backoff would make these tests a minute long."""
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monkeypatch.setattr(supervision, "BACKOFF", (0.0,))
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# The quarantine keeps its real length, so it holds until a test cancels it
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# however slow the run is; 50ms here ran out mid-assertion on a loaded run.
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# The one test that wants it to expire shortens it itself.
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async def _settle() -> None:
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"""Let the supervisor work through its restarts."""
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for _ in range(50):
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await asyncio.sleep(0)
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def test_a_crashing_loop_is_restarted():
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attempts = 0
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async def loop() -> None:
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nonlocal attempts
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attempts += 1
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if attempts < 3:
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raise ConnectionError("broker went away")
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async def scenario() -> None:
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supervisor = Supervisor()
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supervisor.spawn("mqtt", "heating", loop)
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await _settle()
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assert attempts == 3
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assert supervisor.quarantined == set()
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await supervisor.cancel_all()
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asyncio.run(scenario())
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def test_a_loop_that_returns_is_left_alone():
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"""Returning is how a loop says it is finished, not that it failed."""
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attempts = 0
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async def loop() -> None:
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nonlocal attempts
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attempts += 1
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async def scenario() -> None:
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supervisor = Supervisor()
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supervisor.spawn("cron", "heating", loop)
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await _settle()
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assert attempts == 1
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await supervisor.cancel_all()
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asyncio.run(scenario())
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def test_a_flow_that_keeps_crashing_is_stood_down():
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attempts = 0
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events: list[dict] = []
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bus = EventBus()
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bus.publish = events.append # type: ignore[method-assign]
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async def loop() -> None:
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nonlocal attempts
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attempts += 1
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raise RuntimeError("nope")
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async def scenario() -> None:
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supervisor = Supervisor(bus)
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supervisor.spawn("mqtt", "heating", loop)
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await _settle()
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# Restarting stops once the budget is gone, rather than spinning forever.
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assert attempts == FAILURE_BUDGET
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assert supervisor.quarantined == {"heating"}
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assert [e["type"] for e in events].count("task_crashed") == FAILURE_BUDGET
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quarantine = [e for e in events if e["type"] == "flow_quarantined"][-1]
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assert quarantine["retry_in_s"] == QUARANTINE_BACKOFF[0]
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await supervisor.cancel_all()
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asyncio.run(scenario())
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def test_one_flows_failure_does_not_stand_another_down():
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ran = 0
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async def failing() -> None:
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raise RuntimeError("nope")
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async def healthy() -> None:
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nonlocal ran
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ran += 1
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await asyncio.sleep(3600)
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async def scenario() -> None:
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supervisor = Supervisor()
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supervisor.spawn("a", "broken", failing)
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supervisor.spawn("b", "fine", healthy)
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await _settle()
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assert supervisor.quarantined == {"broken"}
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assert ran == 1
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await supervisor.cancel_all()
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asyncio.run(scenario())
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def test_two_tasks_on_one_flow_do_not_spend_each_others_budget():
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"""A subscriber and publisher each get a full restart budget."""
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tries = {"sub": 0, "pub": 0}
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def crasher(which: str):
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async def loop() -> None:
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tries[which] += 1
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raise ConnectionError("broker went away")
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return loop
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async def scenario() -> None:
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supervisor = Supervisor()
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supervisor.spawn("power.cerbo:mqtt", "power", crasher("sub"))
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supervisor.spawn("power.keepalive:mqtt-out", "power", crasher("pub"))
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await _settle()
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assert tries == {"sub": FAILURE_BUDGET, "pub": FAILURE_BUDGET}
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await supervisor.cancel_all()
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asyncio.run(scenario())
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def test_a_quarantine_expires_and_the_task_tries_again(
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monkeypatch: pytest.MonkeyPatch,
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):
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"""The whole point: a broker that comes back is picked up without a human."""
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monkeypatch.setattr(supervision, "QUARANTINE_BACKOFF", (0.05,))
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attempts = 0
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async def loop() -> None:
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nonlocal attempts
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attempts += 1
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if attempts <= FAILURE_BUDGET:
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raise ConnectionError("broker went away")
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await asyncio.sleep(3600)
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async def scenario() -> None:
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supervisor = Supervisor()
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supervisor.spawn("mqtt", "power", loop)
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await _settle()
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assert attempts == FAILURE_BUDGET
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assert supervisor.quarantined == {"power"}
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# Sit out the rest, shortened to 50ms above.
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await asyncio.sleep(0.1)
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await _settle()
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assert attempts == FAILURE_BUDGET + 1
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assert supervisor.quarantined == set()
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await supervisor.cancel_all()
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asyncio.run(scenario())
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def test_cancel_all_is_idempotent():
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async def loop() -> None:
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await asyncio.sleep(3600)
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async def scenario() -> None:
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supervisor = Supervisor()
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supervisor.spawn("mqtt", "heating", loop)
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await _settle()
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await supervisor.cancel_all()
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await supervisor.cancel_all()
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asyncio.run(scenario())
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def test_cancelling_one_flow_leaves_another_flows_tasks_running():
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"""Rebuilding one flow must not take every other flow's loops with it."""
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async def loop() -> None:
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await asyncio.sleep(3600)
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async def scenario() -> None:
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supervisor = Supervisor()
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supervisor.spawn("gone.sub", "gone", loop)
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supervisor.spawn("fine.sub", "fine", loop)
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await _settle()
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survivor = supervisor._tasks["fine.sub"]
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await supervisor.cancel_flow("gone")
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assert list(supervisor._tasks) == ["fine.sub"]
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assert not survivor.done()
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await supervisor.cancel_all()
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asyncio.run(scenario())
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def test_cancelling_one_flow_lifts_only_its_quarantine():
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async def failing() -> None:
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raise RuntimeError("nope")
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async def scenario() -> None:
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supervisor = Supervisor()
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supervisor.spawn("a", "broken", failing)
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supervisor.spawn("b", "also-broken", failing)
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await _settle()
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assert supervisor.quarantined == {"broken", "also-broken"}
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await supervisor.cancel_flow("broken")
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assert supervisor.quarantined == {"also-broken"}
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# And its budget, or the flow would be quarantined again on the first
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# crash after the rebuild that was meant to fix it.
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assert "a" not in supervisor._failures
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assert "b" in supervisor._failures
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await supervisor.cancel_all()
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asyncio.run(scenario())
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def test_the_restart_steps_are_read_from_the_environment(monkeypatch):
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"""A list in an environment variable, so it arrives as JSON."""
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from fluksio.core.config import Settings
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monkeypatch.setenv("FLOW_RESTART_BACKOFF", "[2, 10]")
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assert Settings().FLOW_RESTART_BACKOFF == (2.0, 10.0)
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