Code it Yourself…

A blog on Microsoft Azure and .NET by Carlos Mendible

Run a Precompiled .NET Core Azure Function in a Container

So this morning I found my self browsing through the images Microsoft has published in the Docker Hub and then I saw this one: microsoft/azure-functions-runtime and decided to Run a Precompiled .NET Core Azure Function in a Container.


1. Create a .NET Core lib project

Create a .NET Core lib project.

dotnet new lib --name dni
cd dni
rm .\Class1.cs

2. Add the required references to be able to use Azure Functions API

Be sure to add the following packages to the project. I couldn’t make the sample work with the latest versions of some of the Microsoft.AspNetCore.* packages, so pay special attention to the version parameter.

dotnet add package Microsoft.AspNetCore.Http -v 2.0.0
dotnet add package Microsoft.AspNetCore.Mvc -v 2.0.0
dotnet add package Microsoft.Azure.WebJobs -v 3.0.0-beta4
dotnet add package Microsoft.Extensions.Primitives -v 2.0.0
dotnet add package Newtonsoft.Json -v 10.0.3

3. Modify the Output Path of the project

Edit dni.csproj and the OutputPath property with the following value: wwwroot\bin. The project contents should now look like the following text:

<Project Sdk="Microsoft.NET.Sdk">
    <PackageReference Include="Microsoft.AspNetCore.Http" Version="2.0.0" />
    <PackageReference Include="Microsoft.AspNetCore.Mvc" Version="2.0.0" />
    <PackageReference Include="Microsoft.Azure.WebJobs" Version="3.0.0-beta4" />
    <PackageReference Include="Microsoft.Extensions.Primitives" Version="2.0.0" />
    <PackageReference Include="Newtonsoft.Json" Version="10.0.3" />

4. Create the wwwroot and validate folders

Create two folders. The first one wwwroot will hold all the functions and global configuration. The second one: validate will hold the configuration of the validate function we’ll be deploying.

md wwwroot
md wwwroot/validate

5. Create host.json file in the wwwroot folder

Create a host.json file in the wwwroot folder with the following contents:

{ }

6. Create function.json and run.csx files

In the wwwroot/validate folder create a functions.json file with the following contents:

  "bindings": [
      "authLevel": "anonymous",
      "name": "req",
      "type": "httpTrigger",
      "direction": "in"
  "scriptFile": "..//bin//netstandard2.0//dni.dll",
  "entryPoint": "Dni.HttpTrigger.Run",
  "disabled": false

Note that in functions.json we are specifying the function trigger type as httpTrigger and also specifying the scriptFile and entryPoint.

Now create a run.csx file with the following contents:

//leave this file empty - all the logic is placed within our precompiled function

7. Create an HttpTrigger.cs file to hold your function

Create a HttpTrigger.cs file with the following contents:

namespace Dni
    using System.Collections.Generic;
    using System.Linq;
    using Microsoft.AspNetCore.Http;
    using Microsoft.AspNetCore.Mvc;
    using Microsoft.Azure.WebJobs.Host;

    public class HttpTrigger
        public static IActionResult Run(HttpRequest req, TraceWriter log)
            log.Info("DNI Validation function is processing a request.");

            string dni = req.Query["dni"];

            return dni != null
                ? (ActionResult)new OkObjectResult(ValidateDNI(dni))
                : new BadRequestObjectResult("Please pass a dni on the query string");

        public static bool ValidateDNI(string dni)
            var table = "TRWAGMYFPDXBNJZSQVHLCKE";
            var foreignerDigits = new Dictionary<char, char>()
            { 'X', '0'},
            { 'Y', '1'},
            { 'Z', '2'}
            var numbers = "1234567890";
            var parsedDNI = dni.ToUpper();
            if (parsedDNI.Length == 9)
                var checkDigit = parsedDNI[8];
                parsedDNI = parsedDNI.Remove(8);
                if (foreignerDigits.ContainsKey(parsedDNI[0]))
                    parsedDNI = parsedDNI.Replace(parsedDNI[0], foreignerDigits[parsedDNI[0]]);

                return parsedDNI.Length == parsedDNI.Where(n => numbers.Contains(n)).Count() &&
                    table[int.Parse(parsedDNI) % 23] == checkDigit;

            return false;

Cause I didn’t want to create a simple Hello World sample, this Azure Function Code takes the dni parameter from the query string and validates if the given value is a valid Spanish National Identity Document number.

8. Create a dockerfile

Create a dockerfile with the following contents:

FROM microsoft/azure-functions-runtime:v2.0.0-beta1
ENV AzureWebJobsScriptRoot=/home/site/wwwroot
ADD wwwroot /home/site/wwwroot

Note that once you execute a docker build on the file all the contents of the wwwroot folder will be copied to the /home/site/wwwroot inside the image.

9. Build the project and the docker image

Build the .NET Core project so you get a precompiled funtion and then build the docker image:

dotnet build
docker build -t dni .

10. Create a container and test the function

Run the following to run the Azure Function in a container:

docker run -p 5000:80 dni

Now navigate to: http://localhost:5000/api/validate?dni=54495436H and the page should return true.

You can download all code and files here.

Hope it helps!