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DNS Resolution Failure

DNS resolution failures prevent distributed training from finding nodes, downloading from HF Hub, or connecting to services.

Quick answer

DNS resolution failures prevent distributed training from finding nodes, downloading from HF Hub, or connecting to services.

Infrastructure#dns#hostname#network#infrastructure#resolution

What this failure is

DNS Resolution Failure is a Infrastructure failure seen during ML training runs. DNS resolution failures prevent distributed training from finding nodes, downloading from HF Hub, or connecting to services. Common tags: Dns, Hostname, Network, Infrastructure.

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Why it happens (the mechanism)

DNS server not configured in container. Cluster DNS not reachable. DNS cache corrupted. IPv6 vs IPv4 DNS issue. Corporate DNS blocking external lookups. 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

  • Cannot resolve hostname
  • Connection to master fails
  • HF download fails with DNS error

Common symptoms and what they mean

SymptomWhy it happens
gaierror: [Errno -2] Name or service not knownDNS server not configured in container
Connection refusedCluster DNS not reachable
DNS server unreachableDNS cache corrupted

Which systems are affected

  • Multi-node training
  • HF model downloads
  • Container with DNS issues

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: gaierror: [Errno -2] Name or service not known
  • ✓Verified signal present: Connection refused
  • ✓Verified signal present: DNS server unreachable
  • ✓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

Lambda Bgp Route Withdrawal Region Outage often co-occurs with this failure because both share underlying assumptions about infrastructure; if you fix this entry but still see drift, validate the related primary cause next. lambda bgp route withdrawal region outage →
Kubernetes Gpu Pod Pending often co-occurs with this failure because both share underlying assumptions about infrastructure; if you fix this entry but still see drift, validate the related neighboring cause next. kubernetes gpu pod pending →
Slurm Node Oom often co-occurs with this failure because both share underlying assumptions about infrastructure; if you fix this entry but still see drift, validate the related neighboring cause next. slurm node oom →

Root cause

  • DNS server not configured in container
  • Cluster DNS not reachable
  • DNS cache corrupted
  • IPv6 vs IPv4 DNS issue
  • Corporate DNS blocking external lookups

The fix and how to prevent it

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References

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