3) Backend Traces

Backend tracing allows Sonarly to link backend errors and traces with frontend sessions, giving you full visibility into issues across your stack.

Step 1: Install the Sentry SDK

Node.js
NestJS
Django
FastAPI
Flask

npm install @sentry/node

npm install @sentry/nestjs @sentry/node

pip install sentry-sdk

pip install sentry-sdk[fastapi]

pip install sentry-sdk[flask]

Step 2: Initialize Sentry

Add this at the very top of your entry file, before any other imports:

Express/Fastify/Koa
NestJS
Django
FastAPI
Flask

const Sentry = require("@sentry/node");

Sentry.init({
  dsn: "https://YOUR_PROJECT_KEY@sonarly.dev/YOUR_PROJECT_ID",
  tracesSampleRate: 1.0,
  environment: process.env.NODE_ENV || "development",
});

// Session linking middleware (add before routes)
app.use((req, res, next) => {
  const sessionId = req.headers['x-sonarly-session-id'];
  if (sessionId) Sentry.setTag('sonarly.session_id', sessionId);
  next();
});

// instrument.ts - Create this file
import * as Sentry from "@sentry/nestjs";

Sentry.init({
  dsn: "https://YOUR_PROJECT_KEY@sonarly.dev/YOUR_PROJECT_ID",
  tracesSampleRate: 1.0,
  environment: process.env.NODE_ENV || "development",
});

Then import it at the top of your main.ts:

import './instrument';
// ... rest of imports

Add to both asgi.py and wsgi.py:

import sentry_sdk
from sentry_sdk.integrations.django import DjangoIntegration

sentry_sdk.init(
    dsn="https://YOUR_PROJECT_KEY@sonarly.dev/YOUR_PROJECT_ID",
    traces_sample_rate=1.0,
    environment="production",
    integrations=[
        DjangoIntegration(
            transaction_style="url",
            middleware_spans=True,
            signals_spans=True,
        ),
    ],
    send_default_pii=True,
)

Create middleware.py for session linking:

import sentry_sdk

class SonarlySessionMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        session_id = request.headers.get('x-sonarly-session-id')
        if session_id:
            sentry_sdk.set_tag('sonarly.session_id', session_id)
        return self.get_response(request)

In settings.py, add to MIDDLEWARE and CORS:

MIDDLEWARE = [
    # ... existing middleware ...
    'your_app.middleware.SonarlySessionMiddleware',
]

CORS_ALLOW_HEADERS = [
    # ... existing headers ...
    'x-sonarly-session-id',
]

import sentry_sdk

sentry_sdk.init(
    dsn="https://YOUR_PROJECT_KEY@sonarly.dev/YOUR_PROJECT_ID",
    traces_sample_rate=1.0,
    environment="production",
)

# Session linking middleware
@app.middleware("http")
async def link_sonarly_session(request, call_next):
    session_id = request.headers.get("x-sonarly-session-id")
    if session_id:
        sentry_sdk.set_tag("sonarly.session_id", session_id)
    return await call_next(request)

import sentry_sdk
from flask import request

sentry_sdk.init(
    dsn="https://YOUR_PROJECT_KEY@sonarly.dev/YOUR_PROJECT_ID",
    traces_sample_rate=1.0,
    environment="production",
)

# Session linking middleware
@app.before_request
def link_sonarly_session():
    session_id = request.headers.get("x-sonarly-session-id")
    if session_id:
        sentry_sdk.set_tag("sonarly.session_id", session_id)

Step 3: Enable CORS for Session Header

Make sure your backend allows the x-sonarly-session-id header:

Express
FastAPI
Django

const cors = require('cors');

app.use(cors({
  exposedHeaders: ['x-sonarly-session-id'],
  allowedHeaders: ['x-sonarly-session-id']
}));

from fastapi.middleware.cors import CORSMiddleware

app.add_middleware(
    CORSMiddleware,
    allow_headers=["x-sonarly-session-id"],
    expose_headers=["x-sonarly-session-id"],
)

# settings.py
CORS_ALLOW_HEADERS = [
    'x-sonarly-session-id',
    # ... other headers
]

DSN Format

Your DSN can be found in the Sonarly dashboard. It follows this format:

https://YOUR_PROJECT_KEY@sonarly.dev/YOUR_PROJECT_ID

Verify

After deploying, check that:

Backend errors appear in your Sonarly dashboard
Errors are linked to frontend sessions (you’ll see the session replay)
Traces show the full request flow

View AI Alerts

Get notified about critical issues automatically

Overview

Features

3) Backend Traces

Step 1: Install the Sentry SDK

Step 2: Initialize Sentry

Step 3: Enable CORS for Session Header

DSN Format

Verify

View AI Alerts

Overview

Features

​Step 1: Install the Sentry SDK

​Step 2: Initialize Sentry

​Step 3: Enable CORS for Session Header

​DSN Format

​Verify

View AI Alerts

Step 1: Install the Sentry SDK

Step 2: Initialize Sentry

Step 3: Enable CORS for Session Header

DSN Format

Verify