host.json reference for Azure Functions 2.x

The host.json metadata file contains global configuration options that affect all functions for a function app. This article lists the settings that are available for the v2 runtime.

Note

This article is for Azure Functions 2.x. For a reference of host.json in Functions 1.x, see host.json reference for Azure Functions 1.x.

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.

{
    "version": "2.0",
    "aggregator": {
        "batchSize": 1000,
        "flushTimeout": "00:00:30"
    },
    "extensions": {
        "cosmosDb": {},
        "durableTask": {},
        "eventHubs": {},
        "http": {},
        "queues": {},
        "sendGrid": {},
        "serviceBus": {}
    },
    "functions": [ "QueueProcessor", "GitHubWebHook" ],
    "functionTimeout": "00:05:00",
    "healthMonitor": {
        "enabled": true,
        "healthCheckInterval": "00:00:10",
        "healthCheckWindow": "00:02:00",
        "healthCheckThreshold": 6,
        "counterThreshold": 0.80
    },
    "logging": {
        "fileLoggingMode": "debugOnly",
        "logLevel": {
          "Function.MyFunction": "Information",
          "default": "None"
        },
        "applicationInsights": {
            "samplingSettings": {
              "isEnabled": true,
              "maxTelemetryItemsPerSecond" : 5
            }
        }
    },
    "singleton": {
      "lockPeriod": "00:00:15",
      "listenerLockPeriod": "00:01:00",
      "listenerLockRecoveryPollingInterval": "00:01:00",
      "lockAcquisitionTimeout": "00:01:00",
      "lockAcquisitionPollingInterval": "00:00:03"
    },
    "watchDirectories": [ "Shared", "Test" ]
}

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"
    }
}
Property Default Description
batchSize 1000 Maximum number of requests to aggregate.
flushTimeout 00:00:30 Maximum time period to aggregate.

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

applicationInsights

This setting is a child of logging.

Controls the sampling feature in Application Insights.

{
    "applicationInsights": {
        "sampling": {
          "isEnabled": true,
          "maxTelemetryItemsPerSecond" : 5
        }
    }
}
Property Default Description
isEnabled true Enables or disables sampling.
maxTelemetryItemsPerSecond 5 The threshold at which sampling begins.

cosmosDb

Configuration setting can be found in Cosmos DB triggers and bindings.

durableTask

Configuration setting can be found in bindings for Durable Functions.

eventHub

Configuration settings can be found in Event Hub triggers and bindings.

extensions

Property that returns an object that contains all of the binding-specific settings, such as http and eventHub.

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 depends on the runtime version. In version 2.x, the default value for an App Service plan is 30 minutes. In version 1.x, it's 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
    }
}
Property Default Description
enabled true Specifies whether the feature is enabled.
healthCheckInterval 10 seconds The time interval between the periodic background health checks.
healthCheckWindow 2 minutes A sliding time window used in conjunction with the healthCheckThreshold setting.
healthCheckThreshold 6 Maximum number of times the health check can fail before a host recycle is initiated.
counterThreshold 0.80 The threshold at which a performance counter will be considered unhealthy.

http

Configuration settings can be found in http triggers and bindings.

{
    "http": {
        "routePrefix": "api",
        "maxOutstandingRequests": 200,
        "maxConcurrentRequests": 100,
        "dynamicThrottlesEnabled": true
    }
}
Property Default Description
routePrefix api The route prefix that applies to all routes. Use an empty string to remove the default prefix.
maxOutstandingRequests 200* The maximum number of outstanding requests that are held at any given time. This limit includes requests that are queued but have not started executing, as well as any in progress executions. Any incoming requests over this limit are rejected with a 429 "Too Busy" response. That allows callers to employ time-based retry strategies, and also helps you to control maximum request latencies. This only controls queuing that occurs within the script host execution path. Other queues such as the ASP.NET request queue will still be in effect and unaffected by this setting. *The default for version 1.x is unbounded. The default for version 2.x in a consumption plan is 200. The default for version 2.x in a dedicated plan is unbounded.
maxConcurrentRequests 100* The maximum number of http functions that will be executed in parallel. This allows you to control concurrency, which can help manage resource utilization. For example, you might have an http function that uses a lot of system resources (memory/cpu/sockets) such that it causes issues when concurrency is too high. Or you might have a function that makes outbound requests to a third party service, and those calls need to be rate limited. In these cases, applying a throttle here can help. *The default for version 1.x is unbounded. The default for version 2.x in a consumption plan is 100. The default for version 2.x in a dedicated plan is unbounded.
dynamicThrottlesEnabled true* When enabled, this setting causes the request processing pipeline to periodically check system performance counters like connections/threads/processes/memory/cpu/etc. and if any of those counters are over a built-in high threshold (80%), requests will be rejected with a 429 "Too Busy" response until the counter(s) return to normal levels. *The default for version 1.x is false. The default for version 2.x in a consumption plan is true. The default for version 2.x in a dedicated plan is false.

logging

Controls the logging behaviors of the function app, including Application Insights.

"logging": {
    "fileLoggingMode": "debugOnly",
    "logLevel": {
      "Function.MyFunction": "Information",
      "default": "None"
    },
    "applicationInsights": {
        ...
    }
}
Property Default Description
fileLoggingMode debugOnly Defines what level of file logging is enabled. Options are never, always, debugOnly.
logLevel n/a Object that defines the log category filtering for functions in the app. Version 2.x follows the ASP.NET Core layout for log category filtering. This lets you filter logging for specific functions. For more information, see Log filtering in the ASP.NET Core documentation.
applicationInsights n/a The applicationInsights setting.

queues

Configuration settings can be found in Storage queue triggers and bindings.

sendGrid

Configuration setting can be found in SendGrid triggers and bindings.

serviceBus

Configuration setting can be found in Service Bus triggers and bindings.

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"
    }
}
Property Default Description
lockPeriod 00:00:15 The period that function level locks are taken for. The locks auto-renew.
listenerLockPeriod 00:01:00 The period that listener locks are taken for.
listenerLockRecoveryPollingInterval 00:01:00 The time interval used for listener lock recovery if a listener lock couldn't be acquired on startup.
lockAcquisitionTimeout 00:01:00 The maximum amount of time the runtime will try to acquire a lock.
lockAcquisitionPollingInterval n/a The interval between lock acquisition attempts.

version

The version string "version": "2.0" is required for a function app that targets the v2 runtime.

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