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Functions extension version

Rule ID: check_functions_extension_version · Category: configuration · Section: runtime Severity: warning (non-gating) · Profiles: deploy, full

What it checks

FUNCTIONS_EXTENSION_VERSION in local.settings.json. A missing, legacy (~1/~2/~3), or otherwise non-~4 value is flagged so the app targets the supported v4 Azure Functions runtime. Flex Consumption apps skip — on Flex the runtime is owned by check_flex_runtime_config via functionAppConfig.runtime.

Why it matters

Legacy Azure Functions runtimes (~1/~2/~3) are retired; deploying against them causes host startup failures and unsupported-runtime errors.

Symptoms

Host fails to start; deployment rejected with unsupported runtime version; functions never come online.

Example findings

Missing value:

FUNCTIONS_EXTENSION_VERSION is not set in local.settings.json;
pin it to '~4' for the current Azure Functions runtime.

Legacy value:

FUNCTIONS_EXTENSION_VERSION is '~3', expected '~4'. Legacy runtimes
(~1/~2/~3) are retired; target the v4 runtime.

How to fix

Set FUNCTIONS_EXTENSION_VERSION to ~4 in local.settings.json; the v1/v2/v3 runtimes are retired.

Reference