chore: add dd-trace (#190)

## Motivation

We're collecting logs, but we'd like better observability for the relay
using dd-trace.

## Change Summary

Configure and enable Datadog tracing for the auth relay.

## Merge Checklist

_Choose all relevant options below by adding an `x` now or at any time
before submitting for review_

- [x] PR title adheres to the [conventional
commits](https://www.conventionalcommits.org/en/v1.0.0/) standard
- [x] PR has a changeset
- [x] PR has been tagged with a change label(s) (i.e. documentation,
feature, bugfix, or chore)
- [x] PR includes documentation if necessary
- [x] All commits have been signed

.changeset/quick-laws-smoke.md

@@ -0,0 +1,5 @@
+---
+"@farcaster/auth-relay": minor
+---
+
+chore: add dd-trace

apps/relay/package.json

@@ -20,6 +20,7 @@
     "@fastify/cors": "^8.4.2",
     "@fastify/rate-limit": "^9.0.1",
     "axios": "^1.7.4",
+    "dd-trace": "^5.21.0",
     "dotenv": "^16.3.1",
     "ethers": "^6.0.8",
     "fastify": "^4.24.3",

apps/relay/src/app.ts

@@ -1,3 +1,4 @@
+import tracing from "./tracing";
 import { RelayServer } from "./server";
 import { CHANNEL_TTL, REDIS_URL, RELAY_SERVER_HOST, RELAY_SERVER_PORT } from "./env";
 

apps/relay/src/env.ts

@@ -1,5 +1,8 @@
 import "dotenv/config";
 
+export const ENVIRONMENT = process.env["ENVIRONMENT"] || process.env["DD_ENV"] || "dev";
+export const SERVICE = process.env["DD_SERVICE"] || "auth-relay";
+
 export const LOG_LEVEL = process.env["LOG_LEVEL"] || "warn";
 
 export const CHANNEL_TTL = Number(process.env["CHANNEL_TTL"] || "3600");

apps/relay/src/tracing.ts

@@ -0,0 +1,49 @@
+import tracer from "dd-trace";
+import { ENVIRONMENT, SERVICE } from "./env";
+
+tracer.init({
+  env: ENVIRONMENT,
+  // Service name that appears in the Datadog UI
+  service: SERVICE,
+  // Include trace ID in log messages
+  logInjection: ENVIRONMENT !== "test",
+  // Collect metrics on NodeJS CPU, memory, heap, event loop delay, GC events, etc.
+  // See https://docs.datadoghq.com/tracing/runtime_metrics/nodejs#data-collected
+  // for a list of statsd metrics.
+  runtimeMetrics: ENVIRONMENT !== "test",
+  // Log configuration on startup
+  startupLogs: ENVIRONMENT === "prod",
+});
+
+tracer.use("fastify", {
+  enabled: true,
+  service: SERVICE,
+  blocklist: ["/healthcheck"],
+});
+
+tracer.use("ioredis", {
+  enabled: true,
+  service: SERVICE,
+});
+
+tracer.use("redis", {
+  enabled: true,
+  service: SERVICE,
+});
+
+tracer.use("http", {
+  enabled: true,
+  service: SERVICE,
+});
+
+tracer.use("http2", {
+  enabled: true,
+  service: SERVICE,
+});
+
+tracer.use("net", {
+  enabled: true,
+  service: SERVICE,
+});
+
+export default tracer;

test/client/src/e2e.test.ts

@@ -1,5 +1,4 @@
 import { generatePrivateKey, privateKeyToAccount } from "viem/accounts";
-import { JsonRpcProvider } from "ethers";
 import { RelayServer } from "../../../apps/relay/src/server";
 import { createAppClient, createWalletClient } from "../../../packages/auth-client/src/clients";
 import { viemConnector } from "../../../packages/auth-client/src/clients/ethereum/viemConnector";