correlation-id-middleware

Correlation-ID Middleware

Give every request a correlation id that shows up in every log line, propagates to downstream HTTP/messaging, and ties a user's request together across services — even where full tracing isn't set up.

Input — point it at your project

Works on a target: a project or GitHub URL. Check for existing setup and the HTTP/logging stack: grep -rn "CorrelationId\|X-Correlation\|HttpContext.TraceIdentifier\|UseSerilog\|HttpClient" --include=*.cs <target>.

Middleware

public class CorrelationIdMiddleware(RequestDelegate next)
{
    public const string Header = "X-Correlation-ID";
    public async Task Invoke(HttpContext ctx)
    {
        var id = ctx.Request.Headers.TryGetValue(Header, out var v) && !string.IsNullOrEmpty(v)
            ? v.ToString() : Activity.Current?.TraceId.ToString() ?? Guid.NewGuid().ToString();

        ctx.Items[Header] = id;
        ctx.Response.Headers[Header] = id;                       // echo back to caller
        using (Serilog.Context.LogContext.PushProperty("CorrelationId", id))  // enrich all logs
            await next(ctx);
    }
}
app.UseMiddleware<CorrelationIdMiddleware>();   // early in the pipeline

Propagate to downstream calls

A DelegatingHandler that copies the id onto outbound HttpClient requests:

public class CorrelationHandler(IHttpContextAccessor http) : DelegatingHandler
{
    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage req, CancellationToken ct)
    {
        if (http.HttpContext?.Items[CorrelationIdMiddleware.Header] is string id)
            req.Headers.TryAddWithoutValidation(CorrelationIdMiddleware.Header, id);
        return base.SendAsync(req, ct);
    }
}
// builder.Services.AddHttpClient<T>().AddHttpMessageHandler<CorrelationHandler>();

For messaging, put the id in message headers (publish) and restore it (consume).

Principles

• Reuse the W3C trace id when present — don't invent a parallel id that competes with real tracing; correlation id complements it for log-grep-ability.
• Accept an inbound id (from a gateway/caller) before generating a new one.
• Enrich logs once via LogContext so every line carries it automatically.
• Echo it in the response so clients can report it in bug tickets.