Modern distributed applications cannot be effectively monitored by legacy methods, which are based on handling _predictable _failures. With microservices architecture now  the de facto standard for web applications, effective debugging and diagnostics require that the system be observable — that is, its internal state can be inferred by observing its output.

However, the line between observability and monitoring is often blurry for development teams. In this post, we discuss monitoring, observability, and the relationship between the two. We also mention some of the tools you can use to achieve observability.

Monitoring

Organizations that have embraced the DevOps mindset usually start decomposing the application to a microservices architecture, in order to gain operability and reduce repair time if an incident happens. But as their systems become more complex, they must ensure that they can still gain visibility on — and react in a timely manner to — system failures.

According to the  SRE book by Google, your monitoring system needs to answer two simple questions: “What’s broken, and why?” Monitoring allows you to watch and understand your system’s state using a predefined set of metrics and logs. Monitoring applications lets you detect a  known set of failure modes.

Monitoring is crucial for analyzing long-term trends, for building dashboards, and for alerting. It lets you know how your apps are functioning, how they’re growing, and how they’re being utilized. However, the problem with monitoring complex distributed applications is that production failures are not linear and therefore are difficult to predict.

Having said this, monitoring is still an indispensable tool for building and running microservice-based systems. If the monitoring rules and metrics are straightforward and focused on actionable data, they will provide a reasonably good view of your system’s health. Although monitoring may not make your system wholly immune to failure, it will provide a panoramic view of system behavior and performance in the wild, allowing you to see the impact of any failure and consequent fixes.

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