Enable browser telemetry
The .NET Aspire dashboard can be configured to receive telemetry sent from browser apps. This feature is useful for monitoring client-side performance and user interactions. Browser telemetry requires additional dashboard configuration and that the JavaScript OTEL SDK is added to the browser apps.
This article discusses how to enable browser telemetry in the .NET Aspire dashboard.
Dashboard configuration
Browser telemetry requires the dashboard to enable these features:
- OTLP HTTP endpoint. This endpoint is used by the dashboard to receive telemetry from browser apps.
- Cross-origin resource sharing (CORS). CORS allows browser apps to make requests to the dashboard.
OTLP configuration
The .NET Aspire dashboard receives telemetry through OTLP endpoints. HTTP OTLP endpoints and gRPC OTLP endpoints are supported by the dashboard. Browser apps must use HTTP OLTP to send telemetry to the dashboard because browser apps don't support gRPC.
To configure the gPRC or HTTP endpoints, specify the following environment variables:
DOTNET_DASHBOARD_OTLP_ENDPOINT_URL: The gRPC endpoint to which the dashboard connects for its data.DOTNET_DASHBOARD_OTLP_HTTP_ENDPOINT_URL: The HTTP endpoint to which the dashboard connects for its data.
Configuration of the HTTP OTLP endpoint depends on whether the dashboard is started by the app host or is run standalone.
Configure OTLP HTTP with app host
If the dashboard and your app are started by the app host, the dashboard OTLP endpoints are configured in the app host's launchSettings.json file.
Consider the following example JSON file:
{
"$schema": "http://json.schemastore.org/launchsettings.json",
"profiles": {
"https": {
"commandName": "Project",
"dotnetRunMessages": true,
"launchBrowser": true,
"applicationUrl": "https://localhost:15887;http://localhost:15888",
"environmentVariables": {
"ASPNETCORE_ENVIRONMENT": "Development",
"DOTNET_ENVIRONMENT": "Development",
"DOTNET_DASHBOARD_OTLP_HTTP_ENDPOINT_URL": "https://localhost:16175",
"DOTNET_RESOURCE_SERVICE_ENDPOINT_URL": "https://localhost:17037",
"DOTNET_ASPIRE_SHOW_DASHBOARD_RESOURCES": "true"
}
},
"http": {
"commandName": "Project",
"dotnetRunMessages": true,
"launchBrowser": true,
"applicationUrl": "http://localhost:15888",
"environmentVariables": {
"ASPNETCORE_ENVIRONMENT": "Development",
"DOTNET_ENVIRONMENT": "Development",
"DOTNET_DASHBOARD_OTLP_HTTP_ENDPOINT_URL": "http://localhost:16175",
"DOTNET_RESOURCE_SERVICE_ENDPOINT_URL": "http://localhost:17037",
"DOTNET_ASPIRE_SHOW_DASHBOARD_RESOURCES": "true",
"ASPIRE_ALLOW_UNSECURED_TRANSPORT": "true"
}
},
"generate-manifest": {
"commandName": "Project",
"launchBrowser": true,
"dotnetRunMessages": true,
"commandLineArgs": "--publisher manifest --output-path aspire-manifest.json",
"applicationUrl": "http://localhost:15888",
"environmentVariables": {
"ASPNETCORE_ENVIRONMENT": "Development",
"DOTNET_ENVIRONMENT": "Development"
}
}
}
}
The preceding launch settings JSON file configures all profiles to include the DOTNET_DASHBOARD_OTLP_HTTP_ENDPOINT_URL environment variable.
Configure OTLP HTTP with standalone dashboard
If the dashboard is used standalone, without the rest of .NET Aspire, the OTLP HTTP endpoint is enabled by default on port 18890. However, the port must be mapped when the dashboard container is started:
docker run --rm -it -d \
-p 18888:18888 \
-p 4317:18889 \
-p 4318:18890 \
--name aspire-dashboard \
mcr.microsoft.com/dotnet/aspire-dashboard:9.0
The preceding command runs the dashboard container and maps gRPC OTLP to port 4317 and HTTP OTLP to port 4318.
CORS configuration
By default, browser apps are restricted from making cross domain API calls. This impacts sending telemetry to the dashboard because the dashboard and the browser app are always on different domains. Configuring CORS in the .NET Aspire dashboard removes the restriction.
If the dashboard and your app are started by the app host, no CORS configuration is required. .NET Aspire automatically configures the dashboard to allow all resource origins.
If the dashboard is used standlone then CORS must be configured manually. The domain used to view the browser app must be configured as an allowed origin by specifing the DASHBOARD__OTLP__CORS__ALLOWEDORIGINS environment variable when the dashboard container is started:
docker run --rm -it -d \
-p 18888:18888 \
-p 4317:18889 \
-p 4318:18890 \
-e DASHBOARD__OTLP__CORS__ALLOWEDORIGINS=https://localhost:8080 \
--name aspire-dashboard \
mcr.microsoft.com/dotnet/aspire-dashboard:9.0
The preceding command runs the dashboard container and configures https://localhost:8080 as an allowed origin. That means a browser app that is accessed using https://localhost:8080 has permission to send the dashboard telemetry.
Multiple origins can be allowed with a comma separated value. Or all origins can be allowed with the * wildcard. For example, DASHBOARD__OTLP__CORS__ALLOWEDORIGINS=*.
For more information, see .NET Aspire dashboard configuration: OTLP CORS.
OTLP endpoint security
Dashboard OTLP endpoints can be secured with API key authentication. When enabled, HTTP OTLP requests to the dashboard must include the API key as the x-otlp-api-key header. By default a new API key is generated each time the dashboard is run.
API key authentication is automatically enabled when the dashboard is run from the app host. Dashboard authentication can be disabled by setting DOTNET_DASHBOARD_UNSECURED_ALLOW_ANONYMOUS to true in the app host's launchSettings.json file.
OTLP endpoints are unsecured by default in the standalone dashboard.
Browser app configuration
A browser app uses the JavaScript OTEL SDK to send telemetry to the dashboard. Successfully sending telemetry to the dashboard requires the SDK to be correctly configured.
OTLP exporter
OTLP exporters must be included in the browser app and configured with the SDK. For example, exporting distributed tracing with OTLP uses the @opentelemetry/exporter-trace-otlp-proto package.
When OTLP is added to the SDK, OTLP options must be specified. OTLP options includes:
url: The address that HTTP OTLP requests are made to. The address should be the dashboard HTTP OTLP endpoint and the path to the OTLP HTTP API. For example,https://localhost:4318/v1/tracesfor the trace OTLP exporter. If the browser app is launched by the app host then the HTTP OTLP endpoint is available from theOTEL_EXPORTER_OTLP_ENDPOINTenvironment variable.headers: The headers sent with requests. If OTLP endpoint API key authentication is enabled thex-otlp-api-keyheader must be sent with OTLP requests. If the browser app is launched by the app host then the API key is available from theOTEL_EXPORTER_OTLP_HEADERSenvironment variable.
Browser metadata
When a browser app is configured to collect distributed traces, the browser app can set the trace parent a browser's spans using the meta element in the HTML. The value of the name="traceparent" meta element should correspond to the current trace.
In a .NET app, for example, the trace parent value would likely be assigned from the Activity.Current and passing its Activity.Id value as the content. For example, consider the following Razor code:
<head>
@if (Activity.Current is { } currentActivity)
{
<meta name="traceparent" content="@currentActivity.Id" />
}
<!-- Other elements omitted for brevity... -->
</head>
The preceding code sets the traceparent meta element to the current activity ID.
Example browser telemetry code
The following JavaScript code demonstrates the initialization of the OpenTelemetry JavaScript SDK and the sending of telemetry data to the dashboard:
import { ConsoleSpanExporter, SimpleSpanProcessor } from '@opentelemetry/sdk-trace-base';
import { DocumentLoadInstrumentation } from '@opentelemetry/instrumentation-document-load';
import { OTLPTraceExporter } from '@opentelemetry/exporter-trace-otlp-proto';
import { registerInstrumentations } from '@opentelemetry/instrumentation';
import { Resource } from '@opentelemetry/resources';
import { SemanticResourceAttributes } from '@opentelemetry/semantic-conventions';
import { WebTracerProvider } from '@opentelemetry/sdk-trace-web';
import { ZoneContextManager } from '@opentelemetry/context-zone';
export function initializeTelemetry(otlpUrl, headers, resourceAttributes) {
const otlpOptions = {
url: `${otlpUrl}/v1/traces`,
headers: parseDelimitedValues(headers)
};
const attributes = parseDelimitedValues(resourceAttributes);
attributes[SemanticResourceAttributes.SERVICE_NAME] = 'browser';
const provider = new WebTracerProvider({
resource: new Resource(attributes),
});
provider.addSpanProcessor(new SimpleSpanProcessor(new ConsoleSpanExporter()));
provider.addSpanProcessor(new SimpleSpanProcessor(new OTLPTraceExporter(otlpOptions)));
provider.register({
// Prefer ZoneContextManager: supports asynchronous operations
contextManager: new ZoneContextManager(),
});
// Registering instrumentations
registerInstrumentations({
instrumentations: [new DocumentLoadInstrumentation()],
});
}
function parseDelimitedValues(s) {
const headers = s.split(','); // Split by comma
const result = {};
headers.forEach(header => {
const [key, value] = header.split('='); // Split by equal sign
result[key.trim()] = value.trim(); // Add to the object, trimming spaces
});
return result;
}
The preceding JavaScript code defines an initializeTelemetry function that expects the OTLP endpoint URL, the headers, and the resource attributes. These parameters are provided by the consuming browser app that pulls them from the environment variables set by the app host. Consider the following Razor code:
@using System.Diagnostics
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>@ViewData["Title"] - BrowserTelemetry</title>
<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.3/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-QWTKZyjpPEjISv5WaRU9OFeRpok6YctnYmDr5pNlyT2bRjXh0JMhjY6hW+ALEwIH" crossorigin="anonymous">
<link rel="stylesheet" href="~/css/site.css" asp-append-version="true" />
@if (Activity.Current is { } currentActivity)
{
<meta name="traceparent" content="@currentActivity.Id" />
}
</head>
<body>
<header>
<nav class="navbar navbar-expand-sm navbar-toggleable-sm navbar-light bg-white border-bottom box-shadow mb-3">
<div class="container">
<a class="navbar-brand" asp-area="" asp-page="/Index">BrowserTelemetry</a>
</div>
</nav>
</header>
<div class="container">
<main role="main" class="pb-3">
@RenderBody()
</main>
</div>
@await RenderSectionAsync("Scripts", required: false)
<script src="scripts/bundle.js"></script>
@if (Environment.GetEnvironmentVariable("OTEL_EXPORTER_OTLP_ENDPOINT") is { Length: > 0 } endpointUrl)
{
var headers = Environment.GetEnvironmentVariable("OTEL_EXPORTER_OTLP_HEADERS");
var attributes = Environment.GetEnvironmentVariable("OTEL_RESOURCE_ATTRIBUTES");
<script>
BrowserTelemetry.initializeTelemetry('@endpointUrl', '@headers', '@attributes');
</script>
}
</body>
</html>
Tip
The bundling and minification of the JavaScript code is beyond the scope of this article.
For the complete working example of how to configure the JavaScript OTEL SDK to send telemetry to the dashboard, see the browser telemetry sample.
