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Alertmanager · English · The edge cases the alertmanager-en docs never spell out

31
ALr/alertmanager-en·posted by zhu_zong·just nowTranslation

The edge cases the alertmanager-en docs never spell out

It took me two weeks of on-and-off digging and plenty of wrong turns. Writing the process down as it happened so the next person spends less time.

One last trap: in container environments remember to adjust the memory-related parameters in step. Otherwise the host limit and the process expectation disagree, and the symptom is intermittent, unreproducible failure.

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13 comments

13 comments

M
Aalice_dev·28 minutes ago

We have run this in production for two years without hitting it. That said, we never reached this scale, so our experience is not really evidence here.

325
Llinlin·12 minutes ago

Worth learning from this debugging approach. We went straight at the logs and took a much longer route.

126
Llinlin·just now

Saved. I am reworking this area this week — this saves a lot of wrong turns.

77
Sslow_query·just now

One counter-example: below alertmanager-en 7.4 the semantics of that code are different, so do not copy it verbatim. We got burned in staging and rolled back once.

126
KkiteMod·12 minutes ago

Has anyone run a controlled experiment? I did, reducing it to a single variable, and the difference was 4% — within noise. So I suspect the main cause is something else.

497
Ttang_hao·2 hours ago

I just read the alertmanager-en source — the author actually explains the reasoning in a comment, roughly "so that it degrades into predictable behaviour in extreme cases".

50
Ttang_haoOP·just nowedited

Can you give a minimal reproduction? I ran it locally for ten minutes and could not reproduce on macOS with the latest version.

16
Sswoole_lee·3 minutes ago

Sharing our numbers, 8 cores 16GB, same scenario:

| Concurrency | P50 | P99 |
|---|---|---|
| 200 | 12ms | 88ms |
| 500 | 31ms | 340ms |

P99 clearly collapses at 500 concurrency, which lines up with your knee point.

9
Zzhou_yi·28 minutes agoedited

There is actually a simpler fix that needs no architecture change: move this check up to the gateway and the problem disappears. The cost is one extra lookup at the gateway.

22
Ddev_zhou·28 minutes agoedited

This matches what we see in production. We only hit it past 3k QPS; the earlier load tests showed nothing — the test traffic was too clean, with no long-tail requests.

70
Llinlin·3 minutes agoedited

This is not a alertmanager-en problem, it is a usage problem. The docs say this API is not thread-safe and you must lock around it yourself.

27
Cchen_dev·2 hours ago

Thanks for sharing real numbers — far more useful than the articles that only cover concepts.

270
Sslow_query·2 days ago

I see point 3 differently. The trade-off depends on your read/write ratio: read-heavy with little writing means caching actually widens the inconsistency window.

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