patternjavascriptModerate
Synthetic monitoring: scripted browser tests for critical user journeys
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synthetic monitoringChecklyPlaywrightuser journeyk6 browserschedule testcheckout flowthird-party failure
Problem
The login endpoint returns 200 and API latency looks normal, but the checkout flow is broken because a third-party payment widget fails to load. HTTP health checks cannot detect application-layer breakage in complex user journeys.
Solution
Use synthetic monitoring to run scripted browser tests against production or staging on a schedule. These tests exercise real user flows end-to-end.
Tools:
Example Checkly check (Playwright):
Run every 5-10 minutes from multiple regions. Alert on failure.
Tools:
- Datadog Synthetics — managed, runs globally, integrates with APM
- Checkly — Playwright-based, developer-friendly, affordable
- Grafana k6 browser — open-source, self-hostable
- GitHub Actions on a schedule — free for open-source, limited probe locations
Example Checkly check (Playwright):
import { test, expect } from '@playwright/test';
test('checkout flow completes successfully', async ({ page }) => {
await page.goto('https://shop.example.com');
await page.click('[data-testid="add-to-cart"]');
await page.click('[data-testid="checkout"]');
await page.fill('#email', 'synthetic-test@example.com');
await expect(page.locator('[data-testid="order-confirmed"]')).toBeVisible({ timeout: 10000 });
});Run every 5-10 minutes from multiple regions. Alert on failure.
Why
Synthetic tests catch application-level failures that infrastructure metrics miss: broken JavaScript, failed third-party dependencies, rendering issues, and broken user flows.
Gotchas
- Use test accounts with fake payment methods — never run synthetics against real payment processors
- Synthetic tests must be idempotent — they run continuously, so they cannot create data that affects other tests
- Flaky synthetic tests cause alert fatigue faster than any other source — fix flakiness immediately or disable the check
- Synthetic test failures often reveal deployment regressions before real user impact — integrate with your deploy pipeline
Context
Detecting production application failures in critical user flows before users report them
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