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Sunday, March 21, 2021

Azure - creating a server-less function in Kotlin


This document describes how to set up a development environment to support the development of a server-less Azure function in Kotlin.

This document DOES NOT describes an application nor it contains specifications about an application.
It only describes the building/preparation/set up of the local development for Azure environment on Linux

Pre-requisite

Before to start is necessary to have some tools/libraries/setting done in the local development machine.

  • IntelliJ Idea

  • node.js ( 1.8 )
    At the moment the best JDK to be used is the 1.8. Newer ones can have problems.

The development machine is a Linux based one (Ubuntu 18.04 LTS).

Is necessary to have installed on the local development machine based on Linux :

After installing Azure CLI and Azure functions core tools, Azure Functions core tools 3 , Microsoft .NET and Maven Apache is possible to start to create the basic project using IntelliJ.

Also be sure to have installed on IntelliJ the Azure Toolkit for IntelliJ and Azure DevOps plugins.

IntelliJ Idea

For all the environments.

Maven Settings

Be sure to have some specific settings for Maven.

From :

  • File/Settings → Build, Execution, Deployment

    • Build Tools → Maven
      Be sure to have the Use Plugin registry box unchecked and the box Work offline unchecked

    • Build Tools → Maven → Importing
      Check the line JDK for importer. Set it with the correct JDK selection, should be 1.8 for this specific project

    • Build Tools → Maven → Repositories
      Verify if the local repository is updated if not hit the button Update

Plugins

Is better to have some plugins installed in IntelliJ Idea before to start to work.

  • Azure Toolkit

  • Azure DevOps

  • Maven helper

  • Maven dependency

 

IMPORTANT !

After modifying the above settings, invalidate the cache and restart everything (will take a while since it has to re-index everything)

File → Invalidate Caches/Restart

Project creation

Create a new project based on Maven and select to install using the archetype.
It is necessary to use the archetype : com.microsoft.azure:azure-functions-kotlin-archetype
Very probably will not be in the list, to add it click on the button Add Archetype and :

  • GroupId : com.microsoft.azure

  • ArtifactId : azure-functions-kotlin-archetype

  • Version : 1.23

  • Repository (optional) : leave empty

Click OK. The archetype will be in the list.
Select it.

Important ! Currently Azure server-less support only JDK 1.8 ! It could work also with more recent ones however warnings will pop up to notify the presence of a wrong JDK.

If everything is OK the project will be created to support a JVM code as server-less function.

Since the archetype is Kotlin based there is not necessary to add the Kotlin support since is already in.

To manually add Kotlin support to a project

  • use the Tools | Kotlin | Configure Kotlin in Project… menu.
    A dialog will ask to specify which modules to enable it in - keep the defaults (All modules).

In the project at this point there are two source code :

  • src/main/java/org.example/Function.kt

  • src/test/java/org.example/FunctionTest.kt

At this point the skeleton project for a server-less function in Kotlin is ready.

To build the code is necessary to “package” it.
To do so, on the right of the IntelliJ Idea editor open the Maven tab :

Under LifeCycle select Clean and then Package

To execute the function, open the Plugins/Azure-functions and select azure-functions:run

To test the Http trigger is possible to do two things.
From a browser, use this URL :

1http://localhost:7071/api/HttpTrigger-Java?name=Steve

The result in the page will be :

Or is possible to open a terminal and execute :

1curl -d "Steve" localhost:7071/api/HttpTrigger-Java

The Http trigger will return the input string (Steve) with “Hello”.

1steve@steve-Precision-T3600:~$ curl -d "Steve" localhost:7071/api/HttpTrigger-Java 2Hello, Steve!steve@steve-Precision-T3600:~$

Login to the Azure CLI

Go on Tools/Azure and select Azure Sign in.
Note ! It is implied the Azure CLI is installed on the machine and already logged in manually. Otherwise is necessary to select the Device Login.
Select the Azure connection to log in.

Deploy the function on Azure

To deploy the function on Azure, from IntelliJ project, Maven tab (on the right) open the Plugins/Azure-functions and select azure-functions:deploy

After the upload the function automatically start to run on the Azure environment.
To see it login in Azure web console and select Function App.

Using the function From Azure

In order to use it, the new URL assigned by the system need to be used.
To retrieve the URL, from the Function App click on the app

From the menu on the left, select Functions

Clicking Functions change the screen.
Select the function (the first time there is only one function, the Http trigger example.

Click on it.
On the new window on the top there is a button : Get Function Url

Click on it and retrieve the URL.To test the function is necessary to use that URL.

So curl will become :

1curl -d "Steve" <url retrieved>.azurewebsites.net/api/HttpTrigger-Java?code=0kOymUA2lfyTtnnajFTYCKTDHPSyvUZnG2J64NYqRZlyRdGYoEyNOQ==

Using a browser the URL to use will be :

1https://<url retrieved>.azurewebsites.net/api/HttpTrigger-Java?code=0kOymUA2lfyTtnnajFTYCKTDHPSyvUZnG2J64NYqRZlyRdGYoEyNOQ==&name=<put your name>

 

 Expanding the project

The default project has an Http trigger. The goal is create a timed trigger in order to call the server-less function at specific time intervals.

To add a new trigger is necessary to use the procedure from the Maven tab for Azure : azure-functions:add

A menu will appear in the run area with the choice of trigger to be added :

Note that the generated code is in Java and NOT Kotlin, so is necessary to convert it.
If everything is set correctly will be enough to open the java code and press Ctrl-Shift-Alt-K to automatically convert it in Kotlin.

Depending the type of trigger to add is necessary to have also other libraries installed, like the Microsoft .NET one.

Troubleshooting

Missing information on local.settings.json

With any trigger other than the Http is necessary to populate the file local.settings.json file with information about the server-less function on Azure.

If trying to run the code in local ends up with an error and the error indicates missing values in the local.settings.json file, it is necessary to update it with some info from the Azure account.
The best way to do so is :

  • open the terminal at the bottom of IntelliJ

  • login to the Azure environment :

    1az login

  • after the login execute the command :

    1func azure functionapp fetch-app-settings <application name>

    To retrieve the application name go on the Azure account via browser and go on the Function App.
    Note ! This will work ONLY if at least one deployment was done !!

    After this call the local.setting.json file will be updated.

  • From the Maven tab :

    • Clean the project (Azure Kotlin Function → Lifecycle → Clean)

    • Package the project (Azure Kotlin Function → Lifecycle → Package)

    • Run the project (Azure Kotlin Function → Plugins → azure-functions:run)

 


References

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