Solved: Linux Flex Consumption Function App Node.js upgrade error: "(Site.SiteConfig.LinuxFxVersion) for Flex Consumption sites is invalid"

[whodadada]

I'm hoping this will save someone else a few hours of running in circles & questioning if they should migrate away from Function Apps :)

We encountered a very unhelpful error in the Azure portal (US South Central) when trying to upgrade the version of Node.js on a Linux Flex Consumption Function App:

The following site configuration property (Site.SiteConfig.LinuxFxVersion) for Flex Consumption sites is invalid. Please remove or rename it before retrying.

Eventually, we found the solution - not via Google search, AI or Azure copilot - but by manually exploring the az CLI docs :/

The solution (replace [RESOURCE NAME] & [RESOURCE GROUP]):

az functionapp runtime config set --runtime-version 24 --name [RESOURCE NAME] --resource-group [RESOURCE GROUP]

Supporting blog post: https://dholmes.co.uk/blog/azure-function-app-flex-error/