Customize JRE used by Azure Functions

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For Windows plan:

• Open Kudu: https://docs.microsoft.com/en-us/azure/azure-functions/functions-how-to-use-azure-function-app-settings#kudu

• You can use one of the Azure JREs or you can bring you own JRE

  • Use one of the Azure JREs
    • Find the JRE you would like to use, which can be located at D:\Program Files\Java\
    • Add AppSetting Key languageWorkers:java:defaultExecutablePath with value set to full path to the required java.exe, for example - D:\Program Files\Java\<version>\bin\java.exe
  • Bring you own JRE
    • 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.exe

• 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:

• You can build your own image or you can use previous azure function image

  • Build your own image

    • 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 building 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

  • Use previous azure function image

    • Please follow Manual version updates on linux