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Flex Consumption runtime config

Rule ID: check_flex_runtime_config · Category: configuration · Section: runtime Severity: error (gating) on an unsupported runtime, warning on a legacy linuxFxVersion · Profiles: deploy, full · Tier: core

What it checks

For a Flex Consumption app, the runtime declared under functionAppConfig.runtime (name/version):

  • A non-Python or undeclared runtime skips.
  • An unsupported Python version fails against the Flex hosting-plan matrix (Flex supports Python 3.10–3.14).
  • A legacy linuxFxVersion declaration warns — Flex ignores it.

Non-Flex apps skip.

Why it matters

Flex Consumption resolves its runtime from functionAppConfig.runtime and ignores linuxFxVersion; a misdeclared or unsupported runtime version fails to deploy or run.

Symptoms

A Flex app with only linuxFxVersion set has no effective runtime declaration; an unsupported Python version is rejected at deploy time.

Example findings

Unsupported runtime version:

Flex Consumption runtime Python 3.9 is not supported; target a supported
Python runtime (3.10–3.14).

Legacy linuxFxVersion on a Flex app:

linuxFxVersion is declared on a Flex Consumption app, which ignores it;
declare the runtime under functionAppConfig.runtime (name/version) instead.

How to fix

Declare the Flex Consumption runtime under functionAppConfig.runtime (name/version); do not use linuxFxVersion.

Reference