Alertmanager · English · Hiring: remote alertmanager-en engineer (full-time, long-term)

74
ALr/alertmanager-en·posted by nikic·2 hours agoOpen source

Hiring: remote alertmanager-en engineer (full-time, long-term)

Some background first. Our setup is alertmanager-en plus three downstream services, seven figures of daily requests, peaking around nine in the evening.

The first thing was to collapse the variables. We were changing config and upgrading the version at the same time, and afterwards nobody could say which change caused what. We rolled back to moving one variable at a time, re-ran three times, and only then did the curve settle. Tedious, but not skippable.

# Load test: do not jump straight to the max concurrency.
# Ramp it up, otherwise you miss the knee.
for c in 50 100 200 400 800; do
  wrk -t8 -c$c -d60s --latency http://127.0.0.1:8080/api/feed
  sleep 20
done

We also fixed monitoring along the way: replaced average-based alerts with percentiles and split them per endpoint. False alerts dropped by about seventy percent and the on-call rotation visibly cheered up.

What genuinely surprised me was the tail. The average looked great while P99 jumped by an order of magnitude past some threshold. The cause was not alertmanager-en itself but our upstream connection reuse — the load test traffic was too clean and hid the long-tail requests.

On trade-offs, my view is this: if nobody on the team owns this area long-term, do not introduce a second mechanism. With two coexistence you first have to work out which one is even in play when things break, and that costs far more than the performance you saved.

31 comments

31 comments

M
LlinlinOP·12 minutes ago

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.

498
Nnikic·3 minutes ago

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

421
Kkite·2 days ago

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

384
Sswoole_lee·1 hour ago

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.

306
Zzhu_zong·28 minutes ago

Agreeing with the above. One addition: with this option enabled the GC count in your metrics doubles, so adjust the alert threshold at the same time or it will keep firing.

261
Rran_bo·2 days ago

A question: what changes in a container with a 512Mi memory limit? That is how we run it in production.

241
Sslow_query·3 minutes ago

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

140
Bbob_chen·2 days ago

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.

133
LlinlinMod·just nowedited

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.

1
Wwinter·2 days 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.

208
Kkernel_panic·2 days agoedited

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.

2
Mmike_xu·2 days agoLevel 6

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.

173
KkiteOP·12 minutes ago

A question: what changes in a container with a 512Mi memory limit? That is how we run it in production.

102
Hhuang_ke·2 days ago

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.

120
Cchen_devOP·2 hours 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.

27
Hhuang_ke·2 days ago

Agreeing with the above. One addition: with this option enabled the GC count in your metrics doubles, so adjust the alert threshold at the same time or it will keep firing.

63
Zzhu_zong·2 days ago

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.

4
Bbob_chen·1 hour 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.

1
Sslow_query·12 minutes ago

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

90
Zzhou_yi·3 minutes agoLevel 6

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.

1
Mmike_xu·28 minutes 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".

223
Kkite·28 minutes ago

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

120
Kkernel_panicOP·12 minutes ago

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.

12
Kkite·2 hours ago

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.

31
Oops_wang·yesterday

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.

128
NnikicMod·12 minutes agoedited

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.

29
Sswoole_lee·2 days 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".

7
Cchen_dev·3 minutes ago

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

2
Zzhou_yi·yesterday

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.

1
Rrase·2 days ago

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

148
Ddev_zhou·3 minutes ago

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

192

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