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Logging to from Azure Functions

Logging errors from Azure Functions, requires only a few lines of code. We've created a client specifically for Azure Functions.

For Functions v1, make sure to install the Microsoft.Azure.WebJobs in minimum version 2.2.0

Install the newest Elmah.Io.Functions package in your Azure Functions project:

Install-Package Elmah.Io.Functions

Log all uncaught exceptions using the ElmahIoExceptionFilter attribute:

[ElmahIoExceptionFilter("API_KEY", "LOG_ID")]
public static class Function1
    public static void Run([TimerTrigger("0 */1 * * * *")]TimerInfo myTimer, TraceWriter log)
        throw new Exception("Some exception");

Replace API_KEY with your API key (Where is my API key?) and LOG_ID (Where is my log ID?) with your log ID.

If your function method is declared as async, remember to change the return type to Task. Without it, the function host never invoke ElmahIoExceptionFilter.

The filter also supports config variables:

[ElmahIoExceptionFilter("%apiKey%", "%logId%")]

The variables above, would require you to add your API key and log ID to your settings.json:

  "Values": {
    "apiKey": "API_KEY",
    "logId": "LOG_ID"

Adding debug information to error messages

When debugging error messages logged from functions, it may be a good help to add information about the context the failing function is executed in. Contextual information isn't available for exception filters, but you can add it by implementing the following class:

public class DebuggingFilter : FunctionInvocationFilterAttribute
    public override Task OnExecutingAsync(FunctionExecutingContext executingContext, CancellationToken cancellationToken)
        executingContext.Properties.Add("message", executingContext.Arguments.First().Value.ToString());
        executingContext.Properties.Add("connection", ConfigurationManager.AppSettings["connection"]);
        return base.OnExecutingAsync(executingContext, cancellationToken);

In the example, I add two properties (message and connectiction). This is an example only and you will need to add named values matching your setup. Properties added to FunctionExecutingContext are automatically picked up and logged to

Finally, add DebuggingFilter to your function:

public static class MyFunction
    public static async Task Run(string mySbMsg)

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