Correlate between HTTP requests/responses in Azure Functions

The Arcus.WebApi.Logging.AzureFunctions library provides a way to add correlation between HTTP requests for Azure Functions.

How This Works

See the general HTTP correlation page to get a grasp on how HTTP correlation works.

🚩 By default, the W3C Trace-Context specification is used as the default HTTP correlation format in Arcus, but you can go back to the (deprecated) Hierarchical system we had before, by passing HttpCorrelationFormat.Hierarchical to the services.AddHttpCorrelation().

Installation

For this feature, the following package needs to be installed:

PM > Install-Package Arcus.WebApi.Logging.AzureFunctions

Usage for in-process Azure Functions (receiving side)

To make sure the correlation is added to the HTTP response, following additions have to be made in the .Configure methods of the function's startup:

using Microsoft.Azure.Functions.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection;

[assembly: FunctionsStartup(typeof(Startup))]

namespace MyHttpAzureFunction
{
    public class Startup : FunctionsStartup
    {
        public override void Configure(IFunctionsHostBuilder builder)
        {
            builder.AddHttpCorrelation();
        }
    }
}

When this addition is added, you can use the HttpCorrelation inside your function to call the correlation functionality and use the IHttpCorrelationInfoAccessor (like before) to have access to the CorrelationInfo of the HTTP request. This is how you use the W3C HTTP correlation in your application:

using Arcus.WebApi.Logging.Correlation;

public class MyHttpFunction
{
    private readonly AzureFunctionsInProcessHttpCorrelation _httpCorrelation;

    public MyHttpFunction(AzureFunctionsInProcessHttpCorrelation httpCorrelation)
    {
        _httpCorrelation = httpCorrelation;
    }

    [FunctionName("HTTP-Correlation-Example")]
    public async Task<IActionResult> Run(
        [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest req,
        ILogger log)
    {
        log.LogInformation("C# HTTP trigger function processed a request");

        // Easily set the correlation information to the response if you want to expose it.
        _httpCorrelation.AddCorrelationResponseHeaders(req.HttpContext);

         // Easily access correlation information in your application.
        CorrelationInfo correlationInfo = _httpCorrelation.GetCorrelationInfo();
        return new OkObjectResult("This HTTP triggered function executed successfully.");
    }
}

To use the old Hierarchical HTTP correlation, use the following:

using Arcus.WebApi.Logging.Correlation;

public class MyHttpFunction
{
    private readonly HttpCorrelation _httpCorrelation;

    public MyHttpFunction(HttpCorrelation httpCorrelation)
    {
        _httpCorrelation = httpCorrelation;
    }

    [FunctionName("HTTP-Correlation-Example")]
    public async Task<IActionResult> Run(
        [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest req,
        ILogger log)
    {
        log.LogInformation("C# HTTP trigger function processed a request");
        
        if (!_httpCorrelation.TryHttpCorrelate(out string errorMessage))
        {
            return new BadRequestObjectResult(errorMessage);
        }

        // Easily access correlation information in your application.
        CorrelationInfo correlationInfo = _httpCorrelation.GetCorrelationInfo();
        return new OkObjectResult("This HTTP triggered function executed successfully.");
    }
}

Note that the HttpCorrelation already has the registered IHttpCorrelationInfoAccessor embedded but nothing stops you from injecting the IHtpCorrelationInfoAccessor yourself and use that one. Behind the scenes, both instances will be the same.

Usage for isolated Azure Functions (receiving side)

To make sure the correlation is added to the HTTP response, following middleware has to be added in the Program.cs file:

using Microsoft.Extensions.Hosting;

IHost host = new HostBuilder()
    .ConfigureFunctionsWorkerDefaults(builder =>
    {
        builder.UseFunctionContext()
               .UseHttpCorrelation();
    })
    .Build();

host.Run();

• The UseFunctionContext middleware makes sure that the FunctionContext in the Azure Function is accessible via the IFunctionContextAccessor function. This is required since the IHttpCorrelationInfoAccessor uses the FunctionContext to assign the correlation model.
• The UseHttpCorrelation middleware adds the HTTP correlation functionality to the request pipeline. This makes sure that the incoming requests results in a correlation model (accessible via the IHttpCorrelationInfoAccessor) and the outgoing response is enriched with this correlation model.

The HTTP trigger function can access the IHttpCorrelationInfoAccessor but doesn't require any additional changes to make the HTTP correlation work (unlike the in-process Azure Functions variant).

public class HttpTriggerFunction
{
    private readonly IHttpCorrelationInfoAccessor _correlationAccessor;

    public HttpTriggerFunction(IHttpCorrelationInfoAccessor correlationAccessor)
    {
        _correlationAccessor = correlationAccessor;
    }

    [Function("http")]
    public HttpResponseData Run(
        [HttpTrigger(AuthorizationLevel.Function, "post")] HttpRequestData request)
    {
        CorrelationInfo correlationInfo = _correlationAccessor.GetCorrelationInfo();
     
        HttpResponseData response = request.CreateResponse(HttpStatusCode.OK);
        return response;
    }
}