App Service periodically fails because of MISSING dotnet 3.1 framework

Question

This is so frustrating:
Last week: support for dotnet 2.2 was yanked. Spent better part of week upgrading to 3.1 because EFCore 3 broke a lot.

This week: periodically when starting up, container reports it is missing the dotnet 3.1 framework. Stopping and restarting sometimes fixes, it appears to be based on luck. Container is configured for dotnet 3.1 LTS.

Here is the log: (id's redacted)

> 2020-07-07T15:41:39.172Z INFO  - Starting container for site

> 2020-07-07T15:41:39.175Z INFO  - docker run -d -p 7434:8081 --namexxxxxxxxxxxxxxxxxxx_middleware -e WEBSITE_CORS_ALLOWED_ORIGINS=* -e WEBSITE_CORS_SUPPORT_CREDENTIALS=False -e WEBSITE_SITE_NAME=xxxxxxxxxxxxxx -e WEBSITE_AUTH_ENABLED=False -e WEBSITE_ROLE_INSTANCE_ID=0 -e WEBSITE_HOSTNAME=xxxxxxxxxxxxxxxxxxxxx.azurewebsites.net -e WEBSITE_INSTANCE_ID=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx HTTP_LOGGING_ENABLED=1 appsvc/middleware:1.2.8 /Host.ListenUrl=http://0.0.0.0:8081 /Host.DestinationHostUrl=http://xxx.xxx.xxx.xxx:8080 /Host.UseFileLogging=true

> 2020-07-07T15:41:40.383Z INFO  - Initiating warmup request to container xxxxxxxxxx    for site xxxxxxxxxx

> 2020-07-07T15:41:39.033117089Z   _____

> 2020-07-07T15:41:39.033284796Z   /  _  \ __________ _________   ____

> 2020-07-07T15:41:39.033298297Z  /  /_\  \___   /  |  \_  __ \_/ __ \

> 2020-07-07T15:41:39.033306697Z /    |    \/    /|  |  /|  | \/\  ___/

> 2020-07-07T15:41:39.033314297Z \____|__  /_____ \____/ |__|    \___  >

> 2020-07-07T15:41:39.033321998Z         \/      \/                  \/

> 2020-07-07T15:41:39.033329298Z A P P   S E R V I C E   O N   L I N U X

> 2020-07-07T15:41:39.033336598Z

> 2020-07-07T15:41:39.033358299Z Documentation: http://aka.ms/webapp-linux

> 2020-07-07T15:41:39.033365699Z Dotnet quickstart: https://aka.ms/dotnet-qs

> 2020-07-07T15:41:39.033372700Z ASP .NETCore Version: 2.1.18

> 2020-07-07T15:41:39.033380100Z Note: Any data outside '/home' is not persisted

> 2020-07-07T15:41:39.108659099Z Running oryx create-script -appPath /home/site/wwwroot -output /opt/startup/startup.sh -defaultAppFilePath /defaulthome/hostingstart/hostingstart.dll     -bindPort 8080 -userStartupCommand ''

> 2020-07-07T15:41:39.121439142Z Cound not find build manifest file at '/home/site/wwwroot/oryx-manifest.toml'

> 2020-07-07T15:41:39.121721254Z Could not find operation ID in manifest. Generating an operation id...

> 2020-07-07T15:41:39.122045468Z Build Operation ID: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

> 2020-07-07T15:41:40.136468175Z Writing output script to '/opt/startup/startup.sh'

> 2020-07-07T15:41:40.774145038Z Trying to find the startup DLL name...

> 2020-07-07T15:41:40.774185839Z Found the startup D name: xxxxxxxxxxxxxxxxx.Api.dll

> 2020-07-07T15:41:40.774332045Z Running the command: dotnet "xxxxxxxxxxxxxxxx.Api.dll"

> 2020-07-07T15:41:40.796588543Z It was not possible to find any compatible framework version

> **2020-07-07T15:41:40.797642480Z The specified framework 'Microsoft.AspNetCore.App', version '3.1.0' was not found.**

> 2020-07-07T15:41:40.798287804Z   - Check application dependencies and target a framework version installed at:

> 2020-07-07T15:41:40.798831223Z       /usr/share/dotnet/

> 2020-07-07T15:41:40.803789001Z   - Installing .NET Core prerequisites might help resolve this problem:

> 2020-07-07T15:41:40.804344721Z       https://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409

> 2020-07-07T15:41:40.805009845Z   - The .NET Core framework and SDK can be installed from:

> 2020-07-07T15:41:40.805593166Z       https://aka.ms/dotnet-download

> 2020-07-07T15:41:40.806081883Z   - The following versions are installed:

> **2020-07-07T15:41:40.806617602Z       2.1.18 at [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]**

> 2020-07-07T15:41:41.420Z ERROR - Container xxxxxxxxxxxxxxxxxxxxxx for site xxxxxxxxxxxxx has exited, failing site start

> 2020-07-07T15:41:41.420Z INFO  - Initiating warmup request to container xxxxxxxxxxxxxxx_middleware for site xxxxxxxxxxxxxxx

> 2020-07-07T15:41:46.695Z INFO  - Container xxxxxxxxxxxxxxxxxxxxxx_middleware for site xxxxxxxxx initialized successfully and is ready to serve requests.

> 2020-07-07T15:41:46.710Z ERROR - Container xxxxxxxxxxxxxxxxxx didn't respond to HTTP pings on port: 8080, failing site start. See container logs for debugging.

> 2020-07-07T15:41:46.725Z INFO  - Stopping site xxxxxxxxxxxxxxx because it failed during startup.