Stefan Judis

Nočnica Mellifera

Synthetic monitoring is the process of proactively simulating an interaction with a website, application, or API to measure that it’s available and performant in a given scenario. Synthetic monitoring also deals with alerting the right team with as much information as possible if an error or degradation occurs. 

Synthetic monitoring enables software teams to better understand the performance of their application by simulating realistic scenarios, like uptime of a homepage from a location in Europe, or the performance metrics of the entire checkout process in an eCommerce application at high-frequency intervals against production. It reduces risk in your software by lowering the overall time to detect an error that could negatively impact a customer by proactively alerting teams if performance degrades.

Just as automated testing is essential for high-velocity development teams, enabling them to catch bugs and defects by simulating real user flows in testing and preview environments, synthetic monitoring enables teams to continuously monitor for optimal user experiences. Some synthetic monitoring tools, like Checkly, allow engineers to reuse entire end-to-end tests as production monitors. This enables true continuous quality to be practiced by organizations.

At its core, synthetic monitoring is about simulating user interactions with an application to preemptively identify issues before they impact real users. Synthetic monitoring gives developers and operations engineers the confidence that they are one stay one step ahead, ensuring that potential problems are identified and resolved swiftly.

In practice, synthetic monitoring works a lot like automated testing in production. Teams constantly run “tests” against a production environment from global locations. Using a Monitoring as Code workflow, its easy to even reuse real end-to-end tests as monitors, simply by deploying them to infrastructure such as Checkly.

Synthetic monitors can measure uptime, transactions, status response performance and more - all from different regions of the globe set at a pre-configured frequency. 

This enables continuous confidence when making rapid changes to mission-critical services and applications by allowing you to notice issues before your customers do.

Synthetic monitoring plays a pivotal role in understanding an application's behavior under various scenarios. It allows teams to test how their application performs in different geographical locations, under various network conditions, and during peak load times. This insight is critical for applications that cater to a global audience, where performance can vary significantly based on a user's location and the time of day. Here are some other benefits of synthetic monitoring:

Considering your application's essential features, how long would it be acceptable for these to be broken? The answer to this question is your ideal monitoring interval.

You can only fix production issues you know about. If making a purchase is your core business, you probably don't want to test this functionality only once a day after a production deployment. Nor do you want to rely on an observability platform reactive alerting you after a customer has encountered the broken checkout flow.

Synthetic monitoring enables you to test your core functionality daily, every hour, or even every minute. The shorter your synthetic monitoring interval, the quicker your mean time to detect (MTTD) will be. A short MTTD will enable you to fix production issues before your customers reach out to your support channels!

Betting on user experience testing with synthetic monitoring leads to more meaningful alerts. A failed transaction might be an issue, but your infrastructure could handle it gracefully. Alerts based on a broken user experience tell you the entire story and must be treated critically and acted on immediately.

Another benefit of running synthetic monitoring with headless browsers is that you can monitor performance implications while testing core functionality. Is your web app fast enough for customers in Australia? Does it provide a good Core Web Vitals experience? Do core flows like the customer login become slower over time?

Many things can cause performance degradation, but synthetic monitoring will unveil a slower user experience with aggregated performance metrics. You can't fix things you don't know about!

Monitors are run from controlled environments with consistent browser properties and network connections to make root-cause analysis efficient and accurate.

Synthetic monitoring vs Real User Monitoring (RUM)

Real user monitoring, also called RUM or passive monitoring, is another way to analyze and monitor your application. RUM monitoring offers insights into user interactions, performance statistics, and your users' devices and locations in a way that differs greatly from synthetic monitoring.

Unlike synthetic monitoring tools, RUM monitoring tools don't simulate user interactions, but rather record real user interactions. There's nothing for you to script or define. With RUM, an embedded JavaScript snippet records and reports the behavior of actual users back to you so that you can monitor and analyze your applications' performance and health. Your users are the data source! This sounds great, but there are a few challenges with RUM.

Simulates realistic scenarios and interactions

Proactively monitors for errors or degraded performance

Reactively monitors metrics for abnormal data or performance

Only produces traces when an error is encountered

Traces & stores vast amounts of user data you'll need to store.

Safe, secure data used during synthetic runs

May accidentally contain private user information or PII

There are a number of terms used around synthetic monitoring; everything from "Synthetic User Monitoring" to "Heartbeat Checks" can refer to the same test! However, in general, there are four types of monitoring that are most critical for monitoring your production services:

Availability Monitoring is fundamental. Its primary objective is to verify whether a web service or application is accessible at any given time. This type of monitoring simulates user interactions to check the availability of websites, APIs, and servers. It's not just about confirming that a server is up and returning "200 OK" status messages; it's about ensuring that the application is operational and responding as expected.

Transaction Monitoring takes a step further. To know that every part is really working as expected, Transaction Monitoring means simulating complex user transactions or workflows to verify that critical processes, like checkout or login, are working as intended.

Scripts are designed to mimic the path a user would take through the application. This can be as simple as logging in or as complex as completing a multi-step transaction. The goal is to identify performance issues or bugs that might not be evident in other forms of testing. For example, this will reveal whether third-party services have failed, resulting in degraded performance on our own site.

Web Performance Monitoring is all about speed and efficiency. It evaluates how quickly and smoothly your web application loads and operates from the user's perspective. This is a more analog measurement than the Availability or Transaction Monitoring, as exact loading times will vary and won't give simple "up or down" feedback. Web Performance Monitoring can identify technical debt, as small changes to your experience can add up to degraded (or improved!) performance for your end users.

Keyword monitoring entails monitoring for content that is expected to appear in an API response or within a UI. Keyword monitoring can be extremely helpful for commerce sites or other content-driven websites like news publishers and blogs.

Implementing synthetic monitoring effectively ensures you maximize its value in identifying and resolving performance issues. Here are key best practices to follow:

Before you implement synthetic monitoring, identify the most critical user interactions, such as login flows, checkout processes, or API endpoints that drive your business. These are the flows you want to be setting synthetic monitors for. Simulating these core pathways ensures that issues affecting customer satisfaction are detected early.

Set up monitors across geographically distributed data centers to simulate user access from various regions. This practice helps uncover location-specific latency or connectivity issues and ensures a consistent experience for global users.

Craft test scripts that mimic real user behaviors, including complex interactions like multi-step forms or dynamic content loading. Ensure these scripts reflect typical device types, browsers, and network conditions to emulate authentic experiences.

4. Monitor Continuously and Strategically

Schedule monitoring at frequent intervals to capture real-time performance data. Combine this with strategic off-peak monitoring to identify time-sensitive bottlenecks, such as overnight updates or backups affecting availability.

Configure alerts to balance urgency and relevance. Alerts should only trigger for significant issues, avoiding noise from false positives or minor deviations, to ensure your team focuses on critical problems.

Keep monitoring scripts updated to align with application changes. Regular maintenance prevents outdated tests from providing inaccurate results or missing new vulnerabilities.

7. Integrate Synthetic Monitoring with Your CI/CD Pipeline

Incorporate synthetic monitoring checks into your deployment workflows to catch issues before they reach production. Automated tests can act as gatekeepers for performance and functionality.

By following these best practices, you can leverage synthetic monitoring to proactively enhance performance and deliver seamless user experiences.

Here are key use cases where synthetic monitoring shines:

Website Performance Monitoring: Simulate user interactions to measure load times, responsiveness, and overall performance of web pages.

API Monitoring: Ensure APIs are functional and responsive and deliver accurate data to dependent applications or services.

Global Availability Testing: Verify the availability and performance of your applications from various geographical locations.

End-to-End Testing: Test critical user workflows, such as account creation, login, or checkout processes, to ensure seamless experiences.

Third-Party Service Validation: Monitor the performance of integrated third-party services, such as payment gateways or content delivery networks (CDNs).

Mobile App Monitoring: Test app functionalities across different devices, platforms, and network conditions.

Baseline and SLA Verification: Establish performance baselines and ensure compliance with service-level agreements (SLAs).

These use cases make synthetic monitoring essential for delivering reliable and high-performing applications.

To do synthetic monitoring right, you'll either need to run a service totally independently of your existing tech stack or use a SaaS tool. A system to monitor your production services shouldn't go down when your own system does! You'll also need a tool to store past performance data and present it within a dashboard.

Playwright - The leader in browser automation

Backed by Microsoft, Playwright quickly became one of the leaders in synthetic and end-to-end testing. Its ability to control headless browsers while providing a stellar developer experience convinced the developers, quality assurance, and DevOps communities. And we at Checkly believe it's the best tool for synthetic monitoring.

Checkly - The best platform for running Synthetic Tests

While multiple Observability vendors offer limited site pings as part of a larger toolset, Checkly offers the best experience for users focused on synthetics testing. While other teams use Playwright only for the occasional end-to-end checks, Checkly lets you run these detailed checks with complex scripted behavior at any cadence you need to maintain your SLA. And Checkly can cost less than half of what our competitors charge.  
Checkly offers rich options for scheduling tests on a cadence, including scheduling checks from multiple regions, and offers the most complete answer to ‘how is our service performing for all our users?

At Checkly, we’ve pioneered Monitoring as Code to help shift observability left and unite testing and monitoring in the SDLC. With MaC, you can reuse real, end-to-end Playwright tests as monitors, configure alerting and thresholds with code, and deploy Dashboards and Status Pages to communicate your application’s health with internal and external stakeholders.

Synthetic monitoring forms the foundation of shipping a seamless user experience. It is a safety net for development and DevOps teams, allowing them to innovate confidently. By integrating synthetic monitoring with a MaC approach, we create a bridge between testing and monitoring, fostering a collaborative environment that enhances the overall health of your application.

Synthetic monitoring and Monitoring as Code anticipate and resolve issues before they impact users and streamlines the process of maintaining a high-performing, user-centric application. In the fast-paced world of development, synthetic monitoring and MaC are tools and essential practices that ensure your application consistently delivers an optimal user experience.

Because you have to remember you can only fix issues you know about.

The concepts of observability and monitoring aim to provide critical insights into an application's health and performance. And while both seem similar, they differ in their approach to system analysis.

Synthetic monitoring, on the one hand, operates on a set of predefined actions leading to certain results and metrics. It includes calling API endpoints to check for correct and performant responses or controlling headless browsers to simulate user actions and test for functioning UI interactions. Synthetic monitoring looks at your application from the outside and constantly tests that everything operates correctly.

Observability, on the other hand, helps to analyze a system’s internals by scanning and parsing log files, traces, and system events. Thanks to observability you are able to trace events across system boundaries and services. It enables a comprehensive view of your infrastructure, the taken operations, and your system’s overall health and performance.

Both approaches are valuable to guarantee a well-functioning and highly available system, but only in combination do they really shine. Synthetic monitoring enables you to proactively test your application's functionality and get alerted when something is wrong and impacts end user experience. Observability then enables you to find out what’s wrong after getting alerted.

What is the difference between observability and synthetic monitoring?

To ensure that your website and APIs have high availability, synthetic monitoring enables you to constantly test your website’s uptime and the provided functionality. By scheduling automated API calls and headless browser sessions, you can be assured that your website is up and running at any time and from anywhere in the world. 

Synthetic monitoring is a proactive approach to ensure your application works as expected and enables you to receive timely alerts in case something is wrong.

How does synthetic monitoring contribute to maintaining website uptime?

Contrary to older and passive monitoring methods, synthetic monitoring enables you to be proactive and leverage automation scripts to test your application and infrastructure. 

Make API calls or simulated browser sessions to constantly test and monitor your application, gather performance metrics, and most importantly be certain that your application and the underlying infrastructure perform like they’re supposed to. 

Thanks to synthetic monitoring you’ll get alerted and know about issues before your customers do!

What advantages does synthetic monitoring have over older monitoring techniques?

Passive monitoring observes and monitors existing traffic and user interactions. It’s a reactive approach to analyze performed actions and traffic to identify potential issues. Passive monitoring looks at and analyzes existing traffic and it doesn’t lead to any additional requests or browser sessions.

Synthetic or active monitoring simulates user actions such as making API calls or performing a browser session with a real browser. Synthetic monitoring is a proactive approach to test if an application is working correctly globally at all times.

How do passive and synthetic monitoring differ?

Synthetic monitoring enables the collection and capturing of critical performance metrics.

Synthetic API monitoring performs your predefined API calls and collects performance metrics such as Time to first byte (TTFB) or DNS resolution time. It enables you to define thresholds to capture performance regressions and get alerted when your APIs become slower over time.

Synthetic end-to-end monitoring simulates real browser sessions that perform application user flows like buying a product or logging into an account. While navigating your website, common frontend performance metrics such as load time or core web vitals such as largest contentful paint (LCP) and total blocking time (TBT) will be gathered and visualized to discover slow-performing frontends. 

Visualized and captured performance metrics on the API and UI level provide clear insights into user experience and allow you to notice and prevent performance regressions before they become an issue.

How are performance metrics specifically captured and analyzed in synthetic monitoring?

Learn more about synthetic monitoring and how it relates to uptime monitoring and observability.

Frequently asked questions about synthetic monitoring

Synthetic Monitoring: What is it, Challenges, and How to Get Started

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Synthetic Monitoring: What is it, Challenges, and How to Get Started