how to use structured logging in Azure Functions

Question

I am using the relatively new ILogger (vs. TraceWriter) option in Azure functions and trying to understand how logs are captured.

Here's my function:

    public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)]HttpRequestMessage req, ILogger log)
    {
        log.LogTrace("Function 1 {level}", "trace");
        log.LogWarning("Function 1 {level}", "warning");
        log.LogError("Function 1 {level}", "error");

        return req.CreateResponse(HttpStatusCode.OK, "Success!!!!");
    }

When I look at the server logs, the LogFiles directory has a hierarchy.

The yellow highlighted file includes my log statements:

2017-08-19T13:58:31.814 Function started (Id=d40f2ca6-4cb6-4fbe-a05f-006ae3273562)
2017-08-19T13:58:33.045 Function 1 trace
2017-08-19T13:58:33.045 Function 1 warning
2017-08-19T13:58:33.045 Function 1 error
2017-08-19T13:58:33.075 Function completed (Success, Id=d40f2ca6-4cb6-4fbe-a05f-006ae3273562, Duration=1259ms)

The structured directory contains nothing here, but it seems to have various "codeddiagnostic" log statements in my real function applications directory.

What should I expect here? Ultimately, I would like to have a single sink for logging from all of my application components and take advantage of structured logging across the board.

Answer 1

Just FYI: Azure Functions running in isolated mode (.NET5 and .NET6) don't support structured logging using the ILogger from DI or provided in the FunctionContext. As of November 2021, there is an open bug about it: https://github.com/Azure/azure-functions-dotnet-worker/issues/423

As I understand it, the bug happens because all ILogger calls goes through the GRPC connection between the host and the isolated function, and in that process the message gets formatted instead of sending the original format and arguments. The Azure Insights connection that would record the structured log runs on the host and only receives the final message.

I plan on investigating some king of workaround, playing with direct access to Azure Insights inside the isolated process. If it works, I'll post the workaround in a comment at the bug linked above.