host.json reference for Azure Functions 1.x

The host.json metadata file contains configuration options that affect all functions in a function app instance. This article lists the settings that are available for the version 1.x runtime. The JSON schema is at http://json.schemastore.org/host.

Other function app configuration options are managed in your app settings.

Some host.json settings are only used when running locally in the local.settings.json file.

Sample host.json file

The following sample host.json files have all possible options specified.

{
    "aggregator": {
        "batchSize": 1000,
        "flushTimeout": "00:00:30"
    },
    "applicationInsights": {
        "sampling": {
          "isEnabled": true,
          "maxTelemetryItemsPerSecond" : 5
        }
    },
    "documentDB": {
        "connectionMode": "Gateway",
        "protocol": "Https",
        "leaseOptions": {
            "leasePrefix": "prefix"
        }
    },
    "eventHub": {
      "maxBatchSize": 64,
      "prefetchCount": 256,
      "batchCheckpointFrequency": 1
    },
    "functions": [ "QueueProcessor", "GitHubWebHook" ],
    "functionTimeout": "00:05:00",
    "healthMonitor": {
        "enabled": true,
        "healthCheckInterval": "00:00:10",
        "healthCheckWindow": "00:02:00",
        "healthCheckThreshold": 6,
        "counterThreshold": 0.80
    },
    "http": {
        "routePrefix": "api",
        "maxOutstandingRequests": 20,
        "maxConcurrentRequests": 10,
        "dynamicThrottlesEnabled": false
    },
    "id": "9f4ea53c5136457d883d685e57164f08",
    "logger": {
        "categoryFilter": {
            "defaultLevel": "Information",
            "categoryLevels": {
                "Host": "Error",
                "Function": "Error",
                "Host.Aggregator": "Information"
            }
        }
    },
    "queues": {
      "maxPollingInterval": 2000,
      "visibilityTimeout" : "00:00:30",
      "batchSize": 16,
      "maxDequeueCount": 5,
      "newBatchThreshold": 8
    },
    "sendGrid": {
        "from": "Contoso Group <admin@contoso.com>"
    },
    "serviceBus": {
      "maxConcurrentCalls": 16,
      "prefetchCount": 100,
      "autoRenewTimeout": "00:05:00",
      "autoComplete": true
    },
    "singleton": {
      "lockPeriod": "00:00:15",
      "listenerLockPeriod": "00:01:00",
      "listenerLockRecoveryPollingInterval": "00:01:00",
      "lockAcquisitionTimeout": "00:01:00",
      "lockAcquisitionPollingInterval": "00:00:03"
    },
    "tracing": {
      "consoleLevel": "verbose",
      "fileLoggingMode": "debugOnly"
    },
    "watchDirectories": [ "Shared" ],
}

The following sections of this article explain each top-level property. All are optional unless otherwise indicated.

aggregator

Specifies how many function invocations are aggregated when calculating metrics for Application Insights.

{
    "aggregator": {
        "batchSize": 1000,
        "flushTimeout": "00:00:30"
    }
}

Function invocations are aggregated when the first of the two limits are reached.

applicationInsights

Controls the sampling feature in Application Insights.

{
    "applicationInsights": {
        "sampling": {
          "isEnabled": true,
          "maxTelemetryItemsPerSecond" : 5
        }
    }
}

DocumentDB

Configuration settings for the Azure Cosmos DB trigger and bindings.

{
    "documentDB": {
        "connectionMode": "Gateway",
        "protocol": "Https",
        "leaseOptions": {
            "leasePrefix": "prefix1"
        }
    }
}

durableTask

Configuration settings for Durable Functions.

{
 "extensions": {
  "durableTask": {
    "hubName": "MyTaskHub",
    "storageProvider": {
      "connectionStringName": "AzureWebJobsStorage",
      "controlQueueBatchSize": 32,
      "controlQueueBufferThreshold": 256,
      "controlQueueVisibilityTimeout": "00:05:00",
      "maxQueuePollingInterval": "00:00:30",
      "partitionCount": 4,
      "trackingStoreConnectionStringName": "TrackingStorage",
      "trackingStoreNamePrefix": "DurableTask",
      "useLegacyPartitionManagement": true,
      "workItemQueueVisibilityTimeout": "00:05:00",
    },
    "tracing": {
      "traceInputsAndOutputs": false,
      "traceReplayEvents": false,
    },
    "notifications": {
      "eventGrid": {
        "topicEndpoint": "https://topic_name.chinanorth2-1.eventgrid.chinacloudapi.cn/api/events",
        "keySettingName": "EventGridKey",
        "publishRetryCount": 3,
        "publishRetryInterval": "00:00:30",
        "publishEventTypes": [
          "Started",
          "Pending",
          "Failed",
          "Terminated"
        ]
      }
    },
    "maxConcurrentActivityFunctions": 10,
    "maxConcurrentOrchestratorFunctions": 10,
    "extendedSessionsEnabled": false,
    "extendedSessionIdleTimeoutInSeconds": 30,
    "useAppLease": true,
    "useGracefulShutdown": false,
    "maxEntityOperationBatchSize": 50
  }
 }
}

{
  "extensions": {
    "durableTask": {
      "hubName": "MyTaskHub",
      "controlQueueBatchSize": 32,
      "partitionCount": 4,
      "controlQueueVisibilityTimeout": "00:05:00",
      "workItemQueueVisibilityTimeout": "00:05:00",
      "maxConcurrentActivityFunctions": 10,
      "maxConcurrentOrchestratorFunctions": 10,
      "maxQueuePollingInterval": "00:00:30",
      "azureStorageConnectionStringName": "AzureWebJobsStorage",
      "trackingStoreConnectionStringName": "TrackingStorage",
      "trackingStoreNamePrefix": "DurableTask",
      "traceInputsAndOutputs": false,
      "logReplayEvents": false,
      "eventGridTopicEndpoint": "https://topic_name.chinanorth2-1.eventgrid.chinacloudapi.cn/api/events",
      "eventGridKeySettingName":  "EventGridKey",
      "eventGridPublishRetryCount": 3,
      "eventGridPublishRetryInterval": "00:00:30",
      "eventGridPublishEventTypes": ["Started", "Completed", "Failed", "Terminated"]
    }
  }
}

Task hub names must start with a letter and consist of only letters and numbers. If not specified, the default task hub name for a function app is TestHubName. For more information, see Task hubs.

Many of these settings are for optimizing performance. For more information, see Performance and scale.

eventHub

Configuration settings for Event Hub triggers and bindings.

functions

A list of functions that the job host runs. An empty array means run all functions. Intended for use only when running locally. In function apps in Azure, you should instead follow the steps in How to disable functions in Azure Functions to disable specific functions rather than using this setting.

{
    "functions": [ "QueueProcessor", "GitHubWebHook" ]
}

functionTimeout

Indicates the timeout duration for all functions. In a serverless Consumption plan, the valid range is from 1 second to 10 minutes, and the default value is 5 minutes. In an App Service plan, there is no overall limit and the default is null, which indicates no timeout.

{
    "functionTimeout": "00:05:00"
}

healthMonitor

Configuration settings for Host health monitor.

{
    "healthMonitor": {
        "enabled": true,
        "healthCheckInterval": "00:00:10",
        "healthCheckWindow": "00:02:00",
        "healthCheckThreshold": 6,
        "counterThreshold": 0.80
    }
}

http

Configuration settings for http triggers and bindings.

{
    "http": {
        "routePrefix": "api",
        "maxOutstandingRequests": 200,
        "maxConcurrentRequests": 100,
        "dynamicThrottlesEnabled": true
    }
}

id

The unique ID for a job host. Can be a lower case GUID with dashes removed. Required when running locally. When running in Azure, we recommend that you not set an ID value. An ID is generated automatically in Azure when id is omitted.

If you share a Storage account across multiple function apps, make sure that each function app has a different id. You can omit the id property or manually set each function app's id to a different value. The timer trigger uses a storage lock to ensure that there will be only one timer instance when a function app scales out to multiple instances. If two function apps share the same id and each uses a timer trigger, only one timer runs.

{
    "id": "9f4ea53c5136457d883d685e57164f08"
}

logger

Controls filtering for logs written by an ILogger object or by context.log.

{
    "logger": {
        "categoryFilter": {
            "defaultLevel": "Information",
            "categoryLevels": {
                "Host": "Error",
                "Function": "Error",
                "Host.Aggregator": "Information"
            }
        }
    }
}

queues

Configuration settings for Storage queue triggers and bindings.

{
    "queues": {
      "maxPollingInterval": 2000,
      "visibilityTimeout" : "00:00:30",
      "batchSize": 16,
      "maxDequeueCount": 5,
      "newBatchThreshold": 8
    }
}

SendGrid

Configuration setting for the SendGrind output binding

{
    "sendGrid": {
        "from": "Contoso Group <admin@contoso.com>"
    }
}    

serviceBus

Configuration setting for Service Bus triggers and bindings.

{ 
    "serviceBus": {
      "maxConcurrentCalls": 16,
      "prefetchCount": 100,
      "autoRenewTimeout": "00:05:00",
      "autoComplete": true
    }
}

singleton

Configuration settings for Singleton lock behavior. For more information, see GitHub issue about singleton support.

{
    "singleton": {
      "lockPeriod": "00:00:15",
      "listenerLockPeriod": "00:01:00",
      "listenerLockRecoveryPollingInterval": "00:01:00",
      "lockAcquisitionTimeout": "00:01:00",
      "lockAcquisitionPollingInterval": "00:00:03"
    }
}

tracing

Version 1.x

Configuration settings for logs that you create by using a TraceWriter object. To learn more, see [C# Logging].

{
    "tracing": {
      "consoleLevel": "verbose",
      "fileLoggingMode": "debugOnly"
    }
}

watchDirectories

A set of shared code directories that should be monitored for changes. Ensures that when code in these directories is changed, the changes are picked up by your functions.

{
    "watchDirectories": [ "Shared" ]
}

Next steps