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The operational groups of a modern business depend on IT applications. A finance department needs access to accounting systems. A logistics analyst needs access to data about how well the fleet of delivery vehicles is performing. The sales team constantly queries and updates the customer management system. Different business units will have different business requirements around the availability of applications and services.

A finance department may only need access to accounting systems during business hours. In that case, upgrades and other maintenance can happen during off-hours and would not require the accounting system to be available during that time. The customer management system, however, is typically used 24 hours a day, every day. The sales team expects the application to be available all the time. This means that support engineers need to find ways to update and patch the customer management system while minimizing or even avoiding downtime.

Requirements about availability are formalized in service-level objectives (SLOs). SLOs can be defined in terms of availability, such as being available 99.9 percent of the time. A database system may have SLOs around durability or the ability to retrieve data. For example, the human resources department may have to store personnel data reliably for seven years, and the storage system must guarantee that there is a less than 1 in 10 billion chances of an object being lost. Interactive systems have performance-related SLOs. A web application SLO may require a page loading average response time of 2 seconds with a 95th percentile of 4 seconds.

Logging and monitoring data are used to demonstrate compliance with SLOs. The Cloud Logging service collects information about significant events, such as a disk running out of space. Cloud Monitoring collects metrics from infrastructure, services, and applications such as average CPU utilization during a particular period of time or the number of bytes written to a network in a defined time span. Developers can create reports and dashboards using logging details and metrics to monitor compliance with SLOs. These metrics are known as service-level indicators (SLIs).