Technologies/Flask/gunicorn.log.error

FlaskMetric

gunicorn.log.error

Number of error log messages

Dimensions:None

Technical Annotations (74)

Configuration Parameters (14)

--error-logfilerecommended: /var/log/gunicorn/error.log

enables detailed error logging for startup failures

--preloadrecommended: enabled

loads application code before forking workers to detect import and initialization errors

rate_windowrecommended: 5m

Time window for calculating error rate to smooth transient spikes

error_thresholdrecommended: 0.01

1% error rate threshold triggering critical alert

max_requestsrecommended: 1000

recycles workers after N requests to prevent long-running logging issues

max_requests_jitterrecommended: 100

adds randomness to worker recycling to avoid thundering herd

workersrecommended: 4

reduce worker count to limit concurrent stderr writes during peak hours

PROPAGATE_EXCEPTIONSrecommended: True

Flask config to enable exception propagation to Gunicorn logs

disable_existing_loggersrecommended: False

Top-level key in Django LOGGING dict; prevents disabling Gunicorn's handlers

--log-levelrecommended: debug

Gunicorn CLI parameter controlling log verbosity; propagates to Flask when handlers synchronized

preload_apprecommended: True

Required in Gunicorn config when using custom Dockerfile on Cloud Run to eliminate timeout cycle

timeoutrecommended: 1200

User tested 20-minute timeout but it only延ed each worker death—did not resolve root cause

/var/run/gunicorn.pid

PID file location for targeting master process in shutdown commands

KillModerecommended: mixed

systemd workaround to avoid ERROR logs but prevents graceful worker shutdown

Error Signatures (17)

gunicorn.errors.HaltServer: <HaltServer 'Worker failed to boot.' 3>exception

Worker failed to boot.log pattern

Worker failed to booterror code

gunicorn.errors.HaltServer: HaltServer 'Worker failed to boot.' 3exception

5xxhttp status

status=~"5.."log pattern

status=500http status

RuntimeError: reentrant call inside <_io.BufferedWriter name='<stderr>'>exception

Worker with pid [0-9]+ was terminated due to signal 9log pattern

9error code

Worker with pid %s was terminated due to signal %slog pattern

WORKER TIMEOUT (pid:log pattern

Worker (pid:*) was sent SIGKILL! Perhaps out of memory?log pattern

upstream prematurely closed connection while reading response header from upstreamlog pattern

502http status

Worker (pid:*) was sent SIGTERM!log pattern

15error code

CLI Commands (7)

gunicorn app:app --error-logfile /var/log/gunicorn/error.log --access-logfile /var/log/gunicorn/access.log --preloaddiagnostic

gunicorn app:app --workers=4 --max-requests=1000 --max-requests-jitter=100remediation

gunicorn myapp:server --bind localhost:8000 -chdir /path/to/project --workers 2diagnostic

gunicorn --workers=2 --bind=0.0.0.0:8000 --log-level=debug app:appdiagnostic

kill -TERM $(cat /var/run/gunicorn.pid)remediation

pkill --oldest -TERM "gunicorn"remediation

systemctl stop gunicorn.serviceremediation

Technical References (36)

HaltServerexceptionWORKER_BOOT_ERRORerror codeWSGI applicationcomponentapp.pyfile pathdotenvcomponenthttp_requests_totalcomponentrate()conceptstderrfile pathSIGKILLconceptlogging deadlockconceptgunicorn.arbitercomponentPROPAGATE_EXCEPTIONScomponentFlask endpointcomponent/var/log/upstart/myapp.logfile pathupstartcomponent@server.errorhandlercomponentlogging.config.dictConfigcomponentLOGGING dictionaryconceptgunicorn.errorcomponentapp.loggercomponentWerkzeugcomponentGoogle App EnginecomponentGoogle Cloud RuncomponentB2 instance classcomponentgthread workercomponentB4 instance classcomponentarbiter.pyfile pathmaster processcomponentworker processcomponentWIFSIGNALEDconceptwaitpidconceptsignal handlercomponentSIGTERMconceptsystemdcomponentsession hijackingconceptcache poisoningconcept

Related Insights (20)

Application code errors prevent Gunicorn worker startupcritical

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Incorrect WSGI application entry point prevents worker bootcritical

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Syntax errors or exceptions in application code prevent worker bootcritical

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Missing or misconfigured environment variables cause worker startup crashcritical

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Enable verbose logging to diagnose worker boot failuresinfo

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High 5xx error rate indicates service degradationcritical

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High HTTP 500 error rate triggers critical alertcritical

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Reentrant logging deadlock causes worker termination with SIGKILLcritical

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Gunicorn workers crash with reentrant logging errors causing intermittent downtimecritical

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Flask uncaught exceptions not logged by Gunicornwarning

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Gunicorn logs location for upstart deploymentsinfo

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Flask error handlers not registered when defined in non-imported module with Gunicornwarning

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Gunicorn exceptions hidden when custom Django logging disables existing loggerscritical

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Missing Flask application logs when Gunicorn log level not synchronizedwarning

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Gunicorn workers enter infinite timeout-SIGKILL cycle on Google App Enginecritical

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Gunicorn SIGKILL message incorrectly suggests OOM when memory is availablewarning

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SIGTERM signals to workers create false positive error logs during deploymentswarning

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Worker signal handling failure indicates fatal worker problemcritical

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SIGTERM during graceful shutdown logged as error in v21+warning

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Session hijacking and unauthorized endpoint access via smuggled requestscritical

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