Monitoring tells you when something is wrong. Observability helps you work out why. Google's SRE book says monitoring and alerting let a system tell you when it's broken, or about to break, while the OpenTelemetry project describes observability as being able to understand a system from the outside by asking questions about it, including problems you never predicted. You need monitoring for known failures and observability for the unknown ones, and the two work best together.
These two words often get used as if they mean the same thing. If you run a SaaS product, an online shop or a client facing app, the difference matters, because it decides what data you collect and what your team can answer at three in the morning when something stops working.
Observability vs monitoring at a glance
| Monitoring | Observability | |
|---|---|---|
| Main question | Is something wrong? | Why is this happening? |
| Best at | Known failure modes you can predict | Novel problems, the unknown unknowns |
| Typical output | Dashboards, alerts and pages to a human | The ability to explore and slice data freely |
| Data it relies on | Metrics and checks you chose in advance | Metrics, logs and traces emitted by instrumented code |
| Classic framework | The four golden signals: latency, traffic, errors, saturation | Telemetry signals correlated across a request |
What monitoring means
Google's Site Reliability Engineering book is the clearest source I know. It says monitoring and alerting enable a system to tell us when it's broken, or perhaps what's about to break. It also gives the four golden signals every dashboard should show in some form:
- Latency: how long requests take.
- Traffic: how much demand the system is handling.
- Errors: the rate of requests that fail.
- Saturation: how full the system is.
The book says that if you measure all four and page a human when one of them is problematic, your service will be at least decently covered. It's also firm about noise: you should never trigger an alert simply because something seems a bit weird, because a page interrupts someone's work or even their sleep.
What observability means
The OpenTelemetry project, an open standard for telemetry data, describes observability as letting you understand a system from the outside by asking questions about it without knowing its inner workings. It says this helps you troubleshoot novel problems and answer the question why is this happening.
That only works if your application is instrumented. OpenTelemetry says code must emit signals such as traces, metrics and logs, and that an application is well instrumented when developers don't need to add more instrumentation to troubleshoot an issue.
The three signals
| Signal | Definition, in OpenTelemetry's words |
|---|---|
| Metrics | Aggregations over a period of time of numeric data, such as error rate, CPU use or request rate |
| Logs | Timestamped messages emitted by services or other components |
| Traces | The path a single request takes as it moves through multiple services, made up of spans |
Tracing is the signal that takes you furthest beyond monitoring. OpenTelemetry explains that without tracing, finding the root cause of performance problems in a distributed system can be challenging, because problems are often nondeterministic or too complicated to reproduce locally.
A quick example
Picture a checkout that's suddenly slow. Monitoring fires an alert because latency on the checkout service has crossed your threshold. Good. Observability lets your developer open one slow request, follow its trace through the payment service, the stock check and the database, and see that one database call is taking most of the time. Monitoring found the fire. Observability showed which room it started in.
Uptime and reliability are different things
One line in the OpenTelemetry primer is worth pinning above every team's desk. It says a system could be up the whole time, but if clicking Add to Cart doesn't reliably add the right item, the system is unreliable. Uptime checks alone won't catch that. You need signals measured from the user's point of view, which is why OpenTelemetry describes a good service level indicator as one that measures your service from the perspective of your users.
An open-source stack is explained in our guide to Prometheus versus Grafana.
Do you need both?
Yes, for anything customers rely on. Monitoring gives you fast, simple alerts on the failures you expect. Observability gives you the depth to fix the ones you don't. Google's SRE book adds a practical warning: monitoring a complex application is a significant engineering job in its own right, and simpler, faster systems with better tools for analysis afterwards are what it trends towards. Start simple.
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- Set up the four golden signals and a handful of meaningful alerts first.
- Instrument your code with OpenTelemetry so you're not locked into one vendor.
- Add tracing to the user journeys that make you revenue, like sign up and checkout.
- Review every alert that fires. If nobody acted on it, change it or delete it.
When you're ready to pick a tool, I've compared the best observability tools for logs, metrics and traces. For application performance specifically, see my list of the best APM tools, and if you only need to know whether a site is up, start with free uptime monitoring.
My verdict
Monitoring and observability aren't rivals. Monitoring is the smoke alarm and observability is the ability to walk through the building and find the cause. A small team can start with monitoring and the four golden signals, then add tracing as the product grows. If you're buying a platform, choose one that supports OpenTelemetry, so the data you collect today still works if you switch tools tomorrow.
Two leading platforms are compared in a Datadog versus Dynatrace comparison.
Frequently asked questions
What is the difference between observability and monitoring?
Monitoring tells you when something is broken or about to break. Observability lets you ask questions of your system to understand why, including problems you didn't predict.
What are the four golden signals of monitoring?
Google's SRE book lists latency, traffic, errors and saturation as the four golden signals.
What are the three pillars of observability?
The common signals are metrics, logs and traces, which OpenTelemetry describes in its observability primer.
Can you have observability without monitoring?
You'd still want monitoring alerts for known failures. Observability adds the depth to investigate the problems alerts can't explain.
Is observability just a new name for monitoring?
No. OpenTelemetry describes observability as the ability to understand a system from the outside and answer why something is happening, which goes beyond predefined checks.
