Azure Functions
An Azure service that provides an event-driven serverless compute platform.
5,867 questions
Azure Functions App host is not able to start
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Jakob Nielsen from Make Digital Solutions ApS
0
Reputation points
Since yesterday, the Azure Functions host has not been able to start. No changes have been made to the functions.
I am getting the following output in the trace log:
6/13/2025 13:59 Job host stopped
6/13/2025 13:59 Stopping JobHost
6/13/2025 13:59 0 functions loaded
6/13/2025 13:59 0 functions found (Custom)
6/13/2025 13:59 Reading functions metadata (Custom)
6/13/2025 13:59 Loading functions metadata
6/13/2025 13:59 "ConcurrencyOptions
{
""DynamicConcurrencyEnabled"": false,
""MaximumFunctionConcurrency"": 500,
""CPUThreshold"": 0.8,
""SnapshotPersistenceEnabled"": true
}"
6/13/2025 13:59 "HttpOptions
{
""DynamicThrottlesEnabled"": true,
""EnableChunkedRequestBinding"": false,
""MaxConcurrentRequests"": 100,
""MaxOutstandingRequests"": 200,
""RoutePrefix"": ""api""
}"
6/13/2025 13:59 0 functions loaded
6/13/2025 13:59 0 functions found (Custom)
6/13/2025 13:59 Reading functions metadata (Custom)
6/13/2025 13:59 Loading functions metadata
6/13/2025 13:59 Job host started
6/13/2025 13:59 Host started (10343ms)
6/13/2025 13:59 Host initialized (10330ms)
6/13/2025 13:59 "HttpOptions
{
""DynamicThrottlesEnabled"": true,
""EnableChunkedRequestBinding"": false,
""MaxConcurrentRequests"": 100,
""MaxOutstandingRequests"": 200,
""RoutePrefix"": ""api""
}"
6/13/2025 13:59 "Initializing function HTTP routes
No HTTP routes mapped"
6/13/2025 13:59 No job functions found. Try making your job classes and methods public. If you're using binding extensions (e.g. Azure Storage, ServiceBus, Timers, etc.) make sure you've called the registration method for the extension(s) in your startup code (e.g. builder.AddAzureStorage(), builder.AddServiceBus(), builder.AddTimers(), etc.).
6/13/2025 13:59 Generating 0 job function(s)
6/13/2025 13:59 0 functions loaded
6/13/2025 13:59 0 functions found (Custom)
6/13/2025 13:59 Exceeded language worker restart retry count for runtime:node. Shutting down and proactively recycling the Functions Host to recover
6/13/2025 13:59 Reading functions metadata (Custom)
6/13/2025 13:59 Failed to start language worker process for runtime: node. workerId:b95428fb-2f61-4b79-a39a-11fc6e4dda0c
6/13/2025 13:59 Initializing worker process failed
6/13/2025 13:59 Host lock lease acquired by instance ID '88f52b640d06944933df50d1f5e3a10a'.
6/13/2025 13:59 Loading functions metadata
6/13/2025 13:59 Starting Host (HostId=project-vejle-api, InstanceId=446b2ee0-95b3-4ba7-9e96-3390f9cedb98, Version=4.1040.200.25278, ProcessId=5324, AppDomainId=1, InDebugMode=True, InDiagnosticMode=False, FunctionsExtensionVersion=~4)
6/13/2025 13:59 Starting JobHost
Azure Functions
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Khadeer Ali 5,815 Reputation points Microsoft External Staff Moderator2025-06-13T14:53:14.2133333+00:00 @Jakob Nielsen from Make Digital Solutions ApS ,
Thanks for reaching out.
Based on the logs you've shared, the root cause appears to be that the Azure Functions host isn't detecting any valid functions to load. The message "0 functions loaded" and "No job functions found" confirms that no executable functions were discovered during host startup.
Additionally, the log line "Failed to start language worker process for runtime: node" suggests that the Node.js language worker is failing to initialize, which is critical for Node-based Azure Functions to run.
From my understanding, this typically happens when:
The
function.jsonorindex.jsfiles are missing or incorrectly structured.There's a mismatch or issue with the configured Node.js version.
The directory structure doesn't follow the expected pattern.
There’s an unhandled error during function initialization.
Since you mentioned no recent changes were made, I’d recommend verifying the following just to rule out any silent failures from previous deployments:
Ensure that each function directory contains a valid
function.jsonand entry script (likeindex.js).Confirm that your
host.jsonis syntactically correct and doesn’t have any runtime-breaking configurations.Check your application settings for the correct
WEBSITE_NODE_DEFAULT_VERSION.- Try running the function app locally using
func startto see if any initialization errors are surfaced more clearly.
- Try running the function app locally using
-
Jakob Nielsen from Make Digital Solutions ApS 0 Reputation points
2025-06-14T10:22:58.4733333+00:00 @Khadeer Ali thank you for your reply and suggestions. Much appreciated.
I did a func start in the local repo and it started without any errors or warnings. The functions are recognized, and I was able to execute functions locally.
I think this indicates that functions.json and index.js are OK, that the directory structure is also OK.
Node version is set to Node.js 20 LTS in the Function App. WEBSITE_NODE_DEFAULT_VERSION is set to ~20.
This is the host.json:
{ "version": "2.0", "logging": { "applicationInsights": { "samplingSettings": { "isEnabled": true, "excludedTypes": "Request" } } }, "extensionBundle": { "id": "Microsoft.Azure.Functions.ExtensionBundle", "version": "[4.*, 5.0.0)" }, "functionTimeout": "00:10:00" }
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