Azure function app using FUNCTIONS_REQUEST_BODY_SIZE_LIMIT not working on "warmup"

Question

Hello,

we have a problem with our Azure Function App (Consumption).

We want to upload larger files, so we set up an environment variable: FUNCTIONS_REQUEST_BODY_SIZE_LIMIT with value 524288000.

This works fine.

Until our app goes to sleep:

2025-02-11T14:30:40Z [Information] DrainMode mode enabled
2025-02-11T14:30:40Z [Information] Calling StopAsync on the registered listeners
2025-02-11T14:30:40Z [Information] Call to StopAsync complete, registered listeners are now stopped

because after that the first big upload will fail.

It seem like that the environment variable is not setup yet - because i get following exception:

---

Exception while executing function: Functions.upload Exception binding parameter 'req' Request body too large. The max request body size is 104857600 bytes.

---

and the clients (tested with postman and httpclient) get 500 as response.

In LogStream i see nothing new so the call must be answered / filtered out before the call of our function.

In Application Insights i can see:

2/11/2025, 3:22:25 PM -
ConcurrencyOptions { "DynamicConcurrencyEnabled": false, "MaximumFunctionConcurrency": 500, "CPUThreshold": 0.8, "SnapshotPersistenceEnabled": true }
Severity level: 


2/11/2025, 3:22:25 PM -
HttpOptions { "DynamicThrottlesEnabled": false, "EnableChunkedRequestBinding": false, "MaxConcurrentRequests": -1, "MaxOutstandingRequests": -1, "RoutePrefix": "api" }
Severity level: 


2/11/2025, 3:22:00 PM -
Host lock lease acquired by instance ID '00000000000000000000000040F8C73E'.
Severity level: 


2/11/2025, 3:21:55 PM -
Exception while executing function: Functions.upload
Problem Id: 


2/11/2025, 3:21:55 PM -
Executed 'Functions.upload' (Failed, Id=768b05e5-0f36-4e0e-8e27-7cbbe13354f1, Duration=16ms)
Severity level: 


2/11/2025, 3:21:55 PM -
Exception while executing function: Functions.upload
Problem Id: 


2/11/2025, 3:21:55 PM -
Executing 'Functions.upload' (Reason='This function was programmatically called via the host APIs.', Id=768b05e5-0f36-4e0e-8e27-7cbbe13354f1)
Severity level: 


2/11/2025, 3:21:55 PM -
Job host started
Severity level: 


2/11/2025, 3:21:55 PM -
Host started (261ms)
Severity level: 


2/11/2025, 3:21:55 PM -
The next 5 occurrences of the 'Cleanup' schedule (Cron: '0 0 0 * * *') will be: 02/12/2025 00:00:00Z 02/13/2025 00:00:00Z 02/14/2025 00:00:00Z 02/15/2025 00:00:00Z 02/16/2025 00:00:00Z
Severity level: 


2/11/2025, 3:21:55 PM -
Host initialized (133ms)
Severity level: 


2/11/2025, 3:21:55 PM -
Initializing function HTTP routes Mapped function route 'api/config' [all] to 'config' Mapped function route 'api/v1/download' [get] to 'download' Mapped function route 'api/oauth2-redirect.html' [GET] to 'RenderOAuth2Redirect' Mapped function route 'api/openapi/{version}.{extension}' [GET] to 'RenderOpenApiDocument' Mapped function route 'api/swagger.{extension}' [GET] to 'RenderSwaggerDocument' Mapped function route 'api/swagger/ui' [GET] to 'RenderSwaggerUI' Mapped function route 'api/v1/upload' [post] to 'upload' Mapped function route 'api/version' [all] to 'version'
Severity level: 


2/11/2025, 3:21:55 PM -
HttpOptions { "DynamicThrottlesEnabled": false, "EnableChunkedRequestBinding": false, "MaxConcurrentRequests": -1, "MaxOutstandingRequests": -1, "RoutePrefix": "api" }
Severity level: 


2/11/2025, 3:21:55 PM -
Found the following functions: Host.Functions.Cleanup Host.Functions.config Host.Functions.download Host.Functions.RenderOAuth2Redirect Host.Functions.RenderOpenApiDocument Host.Functions.RenderSwaggerDocument Host.Functions.RenderSwaggerUI Host.Functions.upload Host.Functions.version
Severity level: 


2/11/2025, 3:21:55 PM -
Worker process started and initialized.
Severity level: 


2/11/2025, 3:21:55 PM -
Generating 9 job function(s)
Severity level: 


2/11/2025, 3:21:55 PM -
Starting Host (HostId=XXX, InstanceId=YYY, Version=4.1036.3.3, ProcessId=65, AppDomainId=1, InDebugMode=True, InDiagnosticMode=False, FunctionsExtensionVersion=~4)
Severity level: 


2/11/2025, 3:21:55 PM -
Starting JobHost
Severity level: 


2/11/2025, 3:21:55 PM -
ScaleOptions { "ScaleMetricsMaxAge": "00:02:00", "ScaleMetricsSampleInterval": "00:00:10", "MetricsPurgeEnabled": true, "IsTargetScalingEnabled": true, "IsRuntimeScalingEnabled": false }
Severity level: 


2/11/2025, 3:21:55 PM -
SingletonOptions { "LockPeriod": "00:00:15", "ListenerLockPeriod": "00:01:00", "LockAcquisitionTimeout": "10675199.02:48:05.4775807", "LockAcquisitionPollingInterval": "00:00:05", "ListenerLockRecoveryPollingInterval": "00:01:00" }
Severity level: 


2/11/2025, 3:21:55 PM -
ConcurrencyOptions { "DynamicConcurrencyEnabled": false, "MaximumFunctionConcurrency": 500, "CPUThreshold": 0.8, "SnapshotPersistenceEnabled": true }
Severity level: 


2/11/2025, 3:21:55 PM -
FunctionResultAggregatorOptions { "BatchSize": 1000, "FlushTimeout": "00:00:30", "IsEnabled": true }
Severity level: 


2/11/2025, 3:21:55 PM -
LanguageWorkerOptions { "WorkerConfigs": [ { "Description": { "Language": "dotnet-isolated", "DefaultRuntimeName": null, "DefaultRuntimeVersion": "8.0", "SupportedArchitectures": null, "SupportedOperatingSystems": null, "SupportedRuntimeVersions": null, "SanitizeRuntimeVersionRegex": null, "WorkerIndexing": "true", "Extensions": [ ".dll" ], "UseStdErrorStreamForErrorsOnly": false, "DefaultExecutablePath": "dotnet", "DefaultWorkerPath": "/home/site/wwwroot/abc.dll", "WorkerDirectory": "/home/site/wwwroot", "Arguments": [], "WorkerArguments": null, "IsDisabled": null }, "Arguments": { "ExecutablePath": "dotnet", "ExecutableArguments": [], "WorkerPath": "/home/site/wwwroot/CloudExchangeBackend.dll", "WorkerArguments": [] }, "CountOptions": { "SetProcessCountToNumberOfCpuCores": false, "ProcessCount": 1, "MaxProcessCount": 10, "ProcessStartupInterval": "00:00:10", "ProcessStartupTimeout": "00:01:00", "InitializationTimeout": "00:00:10", "EnvironmentReloadTimeout": "00:00:30", "ProcessRestartInterval": "00:00:10", "ProcessShutdownTimeout": "00:00:10" } } ] }
Severity level: 


2/11/2025, 3:21:55 PM -
LoggerFilterOptions { "MinLevel": "None", "Rules": [ { "ProviderName": null, "CategoryName": null, "LogLevel": "Warning", "Filter": null }, { "ProviderName": null, "CategoryName": null, "LogLevel": null, "Filter": "<AddFilter>b__0" }, { "ProviderName": "Microsoft.Azure.WebJobs.Script.WebHost.Diagnostics.WebHostSystemLoggerProvider", "CategoryName": null, "LogLevel": "None", "Filter": null }, { "ProviderName": "Microsoft.Azure.WebJobs.Script.WebHost.Diagnostics.WebHostSystemLoggerProvider", "CategoryName": null, "LogLevel": null, "Filter": "<AddFilter>b__0" }, { "ProviderName": null, "CategoryName": null, "LogLevel": null, "Filter": "<AddFilter>b__0" }, { "ProviderName": "Microsoft.Azure.WebJobs.Script.WebHost.Diagnostics.SystemLoggerProvider", "CategoryName": null, "LogLevel": "None", "Filter": null }, { "ProviderName": "Microsoft.Azure.WebJobs.Script.WebHost.Diagnostics.SystemLoggerProvider", "CategoryName": null, "LogLevel": null, "Filter": "<AddFilter>b__0" } ] }
Severity level: 


2/11/2025, 3:21:55 PM -
ApplicationInsightsLoggerOptions { "SamplingSettings": { "EvaluationInterval": "00:00:15", "InitialSamplingPercentage": 100.0, "MaxSamplingPercentage": 100.0, "MaxTelemetryItemsPerSecond": 20.0, "MinSamplingPercentage": 0.1, "MovingAverageRatio": 0.25, "SamplingPercentageDecreaseTimeout": "00:02:00", "SamplingPercentageIncreaseTimeout": "00:15:00" }, "SamplingExcludedTypes": "Request", "SamplingIncludedTypes": null, "SnapshotConfiguration": null, "EnablePerformanceCountersCollection": true, "HttpAutoCollectionOptions": { "EnableHttpTriggerExtendedInfoCollection": true, "EnableW3CDistributedTracing": true, "EnableResponseHeaderInjection": true }, "LiveMetricsInitializationDelay": "00:00:15", "EnableLiveMetrics": true, "EnableLiveMetricsFilters": true, "EnableQueryStringTracing": false, "EnableDependencyTracking": true, "DependencyTrackingOptions": null, "TokenCredentialOptions": null, "DiagnosticsEventListenerLogLevel": null, "EnableAutocollectedMetricsExtractor": false, "EnableMetricsCustomDimensionOptimization": false }
Severity level: 


2/11/2025, 3:21:55 PM -
9 functions loaded
Severity level: 


2/11/2025, 3:21:55 PM -
0 functions found (Custom)
Severity level: 


2/11/2025, 3:21:55 PM -
Reading functions metadata (Custom)
Severity level: 


2/11/2025, 3:21:55 PM -
Loading functions metadata
Severity level: 

2/11/2025, 3:21:55 PM -
Host initialization: ConsecutiveErrors=0, StartupCount=3, OperationId=ZZZ
Severity level: 


2/11/2025, 3:21:55 PM -
Initializing Host. OperationId: 'ZZZ'.
Severity level: 

2/11/2025, 3:21:55 PM -
Initializing Warmup Extension.
Severity level: 


2/11/2025, 3:21:55 PM -
Skipping WorkerConfig for stack: dotnet-isolated since it is disabled.
Severity level: 


2/11/2025, 3:21:55 PM -
Skipping WorkerConfig for stack: dotnet-isolated since it is disabled.
Severity level: 


2/11/2025, 3:21:54 PM -
Storing keys in a directory '/home/.aspnet/DataProtection-Keys' that may not be persisted outside of the container. Protected data will be unavailable when container is destroyed. For more information go to https://aka.ms/aspnet/dataprotectionwarning
Severity level: 


2/11/2025, 3:21:45 PM -
upload
URL: 

The error does not occur when we are using "App Service" Hosting Plan for our Azure Function.

Please help us - copilot was not able to give us an solution ;-)