03 - Configuration (Flex Consumption)¶

Manage environment settings, runtime options, and host behavior per environment.

Prerequisites¶

Tool	Version	Purpose
Node.js	20+	Local runtime and package execution
Azure Functions Core Tools	v4	Local host and publishing
Azure CLI	2.61+	Azure resource provisioning and management

Flex Consumption plan basics

Flex Consumption (FC1) supports VNet integration, identity-based storage, per-function scaling, and remote build workflows.

What You'll Build¶

You will configure runtime and host settings for a Flex Consumption Function App and verify the effective app configuration.

Infrastructure Context

Plan: Flex Consumption (FC1) | Network: VNet integration supported

This tutorial modifies app settings on an existing Flex Consumption function app.

flowchart TD
    CLI["Azure CLI"] -->|"appsettings set"| FA[Function App\nFlex Consumption FC1]
    FA -->|reads| SETTINGS["App Settings\n• FUNCTIONS_EXTENSION_VERSION\n• languageWorkers__node__arguments"]

    style FA fill:#0078d4,color:#fff
    style SETTINGS fill:#E3F2FD

flowchart LR
    A[Set app settings] --> B[Configure host timeout]
    B --> C[Validate effective config]

Steps¶

Step 1 - Set variables (if not already set)¶

export RG="rg-func-node-flex-demo"
export APP_NAME="<your-function-app-name>"

Step 2 - Configure app settings¶

az functionapp config appsettings set \
  --name "$APP_NAME" \
  --resource-group "$RG" \
  --settings \
    "FUNCTIONS_EXTENSION_VERSION=~4" \
    "languageWorkers__node__arguments=--max-old-space-size=4096"

FUNCTIONS_WORKER_RUNTIME is platform-managed on Flex Consumption

Unlike Consumption and Premium plans, Flex Consumption does not allow setting FUNCTIONS_WORKER_RUNTIME via app settings. Attempting to set it returns an error:

ERROR: The following app setting (Site.SiteConfig.AppSettings.FUNCTIONS_WORKER_RUNTIME)
for Flex Consumption sites is invalid. Please remove or rename it before retrying.

The runtime is configured automatically by the --runtime node parameter during az functionapp create.

Step 3 - Configure host timeout¶

Update host.json with the timeout. Flex Consumption supports unlimited timeout (-1):

{
  "version": "2.0",
  "functionTimeout": "-1"
}

Flex Consumption timeout

Flex Consumption supports "functionTimeout": "-1" for unlimited execution time on HTTP triggers. This is a significant advantage over Consumption (max 10 minutes). Timer and queue triggers may still have platform-imposed limits.

Step 4 - Validate effective config¶

az functionapp config appsettings list \
  --name "$APP_NAME" \
  --resource-group "$RG" \
  --output table

Step 5 - Review Flex Consumption-specific notes¶

Flex Consumption routes all traffic through the integrated VNet by default once configured.
FUNCTIONS_WORKER_RUNTIME is platform-managed — do not set it manually.
Use long-form CLI flags for maintainable runbooks.

Verification¶

The appsettings list command should show at least these settings:

Name                                   Value
-------------------------------------  --------------------------------
FUNCTIONS_EXTENSION_VERSION            ~4
languageWorkers__node__arguments       --max-old-space-size=4096
AzureWebJobsStorage                    DefaultEndpointsProtocol=https;...
APPLICATIONINSIGHTS_CONNECTION_STRING  InstrumentationKey=...

No FUNCTIONS_WORKER_RUNTIME in the list

On Flex Consumption, FUNCTIONS_WORKER_RUNTIME does not appear in app settings because it is managed at the platform level via functionAppConfig.runtime.name.

Next Steps¶

Next: 04 - Logging and Monitoring