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Job Preemption / Spot Instance Termination

Preemption kills cloud spot instances mid-training, losing progress if checkpoints aren't saved frequently enough.

Quick answer

Preemption kills cloud spot instances mid-training, losing progress if checkpoints aren't saved frequently enough.

Reliability#preemption#spot-instance#termination#cloud#signal#graceful-shutdown

What this failure is

Job Preemption / Spot Instance Termination is a Reliability failure seen during ML training runs. Preemption kills cloud spot instances mid-training, losing progress if checkpoints aren't saved frequently enough. Common tags: Preemption, Spot Instance, Termination, Cloud.

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Why it happens (the mechanism)

Cloud provider reclaiming capacity for on-demand usage. Spot market price exceeds bid price. Preemptible instance time limit reached. Taken together, these mechanisms explain why the failure is reproducible, why it tends to surface on specific workloads or scales, and why generic mitigation attempts often fall short without addressing the underlying cause.

What you'll observe

  • Training job terminates with SIGTERM on spot instances
  • Cloud provider reclaims the instance
  • No error other than signal termination

Common symptoms and what they mean

SymptomWhy it happens
Cloud provider sends SIGTERM before instance shutdownCloud provider reclaiming capacity for on-demand usage
Spot instance termination notice receivedSpot market price exceeds bid price
Job terminated with signal 15 (SIGTERM) or signal 9 (SIGKILL)Preemptible instance time limit reached

Which systems are affected

  • AWS EC2 Spot, Azure Spot/Low Priority, GCP Preemptible VMs
  • Large-scale training on spot instances
  • Cost-optimized training infrastructure

How to confirm this is the problem

Use this checklist to test the hypothesis against a small reproduction. No single line proves the root cause, so preserve the preceding events and compare one variable at a time.

  • ✓Reproduce the failure from a clean checkpoint/seed: the symptom must appear without warm-up state from a previous run.
  • ✓Verified signal present: Cloud provider sends SIGTERM before instance shutdown
  • ✓Verified signal present: Spot instance termination notice received
  • ✓Verified signal present: Job terminated with signal 15 (SIGTERM) or signal 9 (SIGKILL)
  • ✓A targeted fix from the "How to fix it" section eliminates or substantially reduces the symptom within one validation pass.

The fix and the prevention pattern

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Related failures to investigate next

Bytedance Sequence Length Straggler often co-occurs with this failure because both share underlying assumptions about reliability; if you fix this entry but still see drift, validate the related primary cause next. bytedance sequence length straggler →
Training Checkpoint Corruption On Write often co-occurs with this failure because both share underlying assumptions about reliability; if you fix this entry but still see drift, validate the related neighboring cause next. training checkpoint corruption on write →
Wandb Tensorboard Failure often co-occurs with this failure because both share underlying assumptions about reliability; if you fix this entry but still see drift, validate the related neighboring cause next. wandb tensorboard failure →

Root cause

  • Cloud provider reclaiming capacity for on-demand usage
  • Spot market price exceeds bid price
  • Preemptible instance time limit reached

The fix and how to prevent it

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References

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