# OpenTelemetry for Cloudflare Workers

Instrument your Cloudflare Worker applications with OpenTelemetry using the the otel-cf-workers SDK.

# Instrumentation

# Step 1: Install the SDK

Install @microlabs/otel-cf-workers in your project.

 terminal
npm i @microlabs/otel-cf-workers 

# Step 2: Add Node.js Compatibility Flags

OpenTelemetry requires the Node.js Compatibility flag is enabled at the top level of your wrangler.toml

 wrangler.toml
compatibility_flags = [ "nodejs_compat" ]

# Step 3: Configure the tracer

In your Cloudflare worker file, add the following configuration code to configure OpenTelemetry.

 index.ts
import { instrument, ResolveConfigFn } from '@microlabs/otel-cf-workers'

export interface Env {
	BASELIME_API_KEY: string
    SERVICE_NAME: string
}

const handler = {
	async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise<Response> {
		// your cloudflare worker code
	},
}

const config: ResolveConfigFn = (env: Env, _trigger) => {
	return {
		exporter: {
			url: 'https://otel.baselime.io/v1',
			headers: { 'x-api-key': env.BASELIME_API_KEY },
		},
		service: { name: env.SERVICE_NAME },
	}
}

export default instrument(handler, config)

# Step 4: Set the Baselime environment variables

In your Cloudflare Workers Secret Configuration add the BASELIME_API_KEY.

To enable tracing for local dev add your BASELIME_API_KEY to your .dev.vars file

 .dev.vars
BASELIME_API_KEY=$YOUR_BASELIME_API_KEY

In your wrangler.toml file set the SERVICE_NAME variable

Get your pulic BASELIME_API_KEY from the Baselime console.

 wrangler.toml
[vars]
SERVICE_NAME = "my-service-name"

Once these steps are completed, distributed traces from your Cloudflare Workers application should be available in Baselime to query via the console or the Baselime CLI.

# Adding custom OpenTelemetry spans

To add custom spans to your OpenTelemetry traces, install the @opentelemetry/api package.

 terminal
npm i @opentelemetry/api

And manually add spans to your traces.

 index.ts
import { trace } from "@opentelemetry/api";
 
const tracer = trace.getTracer('your-custom-traces');

const handler = {
    async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise<Response> {
        const span = trace.getActiveSpan();

        span.setAttribute('search', search)

        const result = await tracer.startActiveSpan(`business-logic`, async (span) => {
            // your business logic
            const input = { search }
            span.setAttributes(input);
            const result = await yourBusinessLogic(input)
            span.setAttributes(result)
            return result
        });
    }
}

# Special Thanks

This is powered by otel-cf-workers developed by Erwin van der Koogh. It's a fantastic vendor agnostic OpenTelemetry SDK for Cloudflare Workers and you should check it out.