Host Logging for EOL or soon-to-be EOL .NET apps

[MadhuraBharadwaj-MSFT]

What problem would the feature you're requesting solve? Please describe.

Show regular warnings when an EOL or soon-to-be EOL version is detected for a .NET app. This warning should be visible and accessible through App Insights.

Describe the solution you'd like

Action	Condition	Behavior	Warning message.
Upon app start/load	Functions version and/or stack version is out of support	Show warning message.	"Upgrade to Functions/Stack version as <stack/functions runtime version> has reached end-of-life on and is no longer supported. Learn more: aka.ms/FunctionsStackUpgrade"
Regular cadence (24h?)	Functions version and/or stack version will be out of support in less than 6 months	Show warning message.	"Use Functions/Stack version as <stack/functions runtime version> will reach end-of-life on and will no longer be supported. Learn more: aka.ms/FunctionsStackUpgrade"

Describe alternatives you've considered

Warnings already exist for such apps in the portal and client tools, but host logging is critical for customer awareness.

Additional context

Current Behavior:
No warning/error is written by Host for EOL apps, and hence these logs are not available on AppInsights.

Acceptance Criteria:
Work item can be marked 'Completed' when we have implemented, tested and deployed the logic to show the above mentioned warning message when an app loads, and at a regular cadence thereafter when a Function App is configured with a stack runtime version that has a) reached its end-of-life date, or b) will reach its end-of-life date in <6months.

Additional information:

1. Getting current stack version information: See this

For Linux:

All stacks - get app runtime version from linux_fx_version (from site config)

For Windows:

Node: WEBSITE_NODE_DEFAULT_VERSION (from app setting)
.NET: netFrameworkVersion (from site config)
Java: javaVersion (from site config)
PowerShell: powerShellVersion (from site config)

2. Compare against EOL dates in StacksAPI: See this