π ~1 min read
Table of contents
Symptom & Impact
Applications randomly fail host lookups, producing intermittent outages and deployment instability.
Environment & Reproduction
Ubuntu 16.04 systems with mixed static and DHCP DNS settings are most likely to reproduce this.
Root Cause Analysis
Resolver configuration drift and upstream nameserver inconsistency cause unresolved or delayed queries.
Quick Triage
Test direct queries against each nameserver and compare with local resolver output.
Step-by-Step Diagnosis
Inspect /etc/resolv.conf ownership, network scripts, and resolver logs while correlating failures with interface renewals.
Solution – Primary Fix
Define a single DNS source of truth, apply explicit nameservers, restart networking, and clear local caches.
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Solution – Alternative Approaches
Deploy a local caching resolver or DNS forwarder to isolate unstable upstream behavior.
Verification & Acceptance Criteria
Repeated dig tests and application transactions succeed through network restarts.
Rollback Plan
Restore previous network profile backups if new resolver order breaks internal domains.
Prevention & Hardening
Manage DNS settings via configuration management and alert on unauthorized resolver edits.
Related Errors & Cross-Refs
Associated symptoms include apt mirror lookup failures and internal API name resolution flaps.
Related tutorial: View the step-by-step tutorial for Ubuntu 16.04 LTS.
View all Ubuntu 16.04 LTS tutorials on the Tutorials Hub β
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
Consult Ubuntu networking references and enterprise DNS operations documentation.
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