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Linux runtime (linuxFxVersion)

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

What it checks

Any Python linuxFxVersion declared in infra config (bicep/ARM, including nested infra/ directories), so Flex Consumption / Linux plan apps target a supported Python runtime. Infra files are scanned for linuxFxVersion declarations such as linuxFxVersion: 'Python|3.12'; no declaration skips.

Why it matters

An unsupported Python runtime encoded in linuxFxVersion causes deployment or cold-start failures on Linux Consumption, Flex Consumption, Premium, and Dedicated plans.

Symptoms

Deployment fails; app stuck in a restart loop; "runtime not supported" errors in the platform logs.

Example finding

```text
Unsupported Python linuxFxVersion runtime(s) in infra config:
- main.bicep: Python|3.9

Fix: target a supported Python runtime (3.10–3.14).

How to fix

Set linuxFxVersion to a supported Python runtime (e.g. Python|3.12) in your infrastructure templates.

Reference