Customize JRE used by Azure Functions

For Windows plan:

• Open Kudu: https://docs.microsoft.com/en-us/azure/azure-functions/functions-how-to-use-azure-function-app-settings#kudu
• Copy your JRE to a folder in d:\home. For example D:\home\MyJre
• Add AppSetting Key languageWorkers:java:defaultExecutablePath with value set to full path to your java.exe, for example d:\home\MyJre\bin\java
• If your app is using consumption plan, you also need add following appsetting. Note: This will increase cold starts for java functions
  • App setting key WEBSITE_USE_PLACEHOLDER with value set to 0

For Linux plan:

• The best practice is to build your own image with the specific jdk version you want to use. Please reference to this link on build your own images: https://github.com/Azure/azure-functions-docker/tree/dev/host/3.0/buster/amd64/java
• After build your own image, update the linuxfxVersion to ping to your own images. Please find more info here https://docs.microsoft.com/en-us/azure/azure-functions/set-runtime-version?tabs=portal#manual-version-updates-on-linux
• Please note this approach only works for dedicated and premium plan. For consumption, there is no Customer Container support