SLI / SLO / SLA

In today’s interconnected world, businesses heavily rely on various services and systems to deliver value to their customers. To ensure the reliability, performance, and quality of these services, organizations employ a framework known as SLI/SLO/SLA.

In this blog, we will explore these concepts in detail and understand how they contribute to service excellence.

When designing a system or application, it's important for teams to set specific measurable targets/goals to help organizations strike the right balance between product development and operation work.

These targets help customers & end users quantify the level of reliability they should come to expect from a service.

Example: “Application should have 97% uptime in a rolling 30-day window”.

Understanding Service Level Indicator(SLI):

SLIs are quantitative measures that provide insights into specific aspects of service performance. They can include metrics such as request latency, error rate, saturation, throughput, and availability.

1. Request Latency: This SLI measures the time taken for a service to respond to a user request. It quantifies the delay or latency experienced by users and helps assess the responsiveness of the system. Lower request latency indicates faster service performance.
2. Error Rate: The error rate SLI measures the proportion of requests that result in errors or failures. It provides insight into the reliability and stability of the service. A lower error rate indicates a more robust and stable system.
3. Saturation: Saturation SLI quantifies the degree to which system resources, such as CPU, memory, or network bandwidth, are utilized. It helps determine if the system is operating near its capacity or becoming overloaded. Monitoring saturation levels assists in capacity planning and preventing performance degradation.
4. Throughput: Throughput SLI measures the rate at which a system processes and handles incoming requests or transactions. It indicates the system’s efficiency and capacity to handle the workload. Higher throughput generally indicates better performance and scalability.
5. Availability: Availability SLI measures the uptime or accessibility of a service, indicating the percentage of time it is operational and accessible to users. It quantifies the reliability and continuity of the service. Higher availability percentages reflect better service reliability.

By tracking SLIs, organizations gain visibility into how well their services are performing, allowing them to identify areas for improvement and make data-driven decisions.

Defining Service Level Objectives(SLO)

Service Level Objectives (SLOs) are predefined targets or goals that organizations set for their SLIs.

These targets reflect the desired level of service quality or performance that a business aims to achieve. For example, an SLO could state that the availability SLI should be 99% or that request latency should be under 200 milliseconds. SLOs provide a clear benchmark against which service performance can be measured and evaluated.

example :

SLI - Latency
SLO – Latency < 100ms

SLI – availability
SLO – 99.9% uptime

💡 SLOs should be directly related to the customer experience. The main purpose of the SLO is to quantify reliability of a product to a customer.

💡 The goal is not to achieve perfection but instead to make customers happy with the right level of reliability.

Service Level Agreement

To solidify the relationship between service providers and customers, SLAs come into play.

SLA stands for Service Level Agreement. It is a formal agreement or contract between a service provider and its customers that define the expected level of service, performance targets, responsibilities, and remedies in case of service disruptions or failures. SLAs are typically established to ensure that the service provider meets the needs and expectations of its customers.

Key elements of an SLA may include:

1. Service Description: A clear description of the services provided, including their scope, features, and functionalities.
2. Service Level Objectives (SLOs): Specific performance targets or goals that the service provider commits to achieving. These SLOs are often defined using Service Level Indicators (SLIs) as discussed earlier.
3. Metrics and Measurements: The specific metrics or SLIs that will be used to measure the performance or quality of the service, along with the frequency and methods of measurement.
4. Responsibilities and Roles: The responsibilities of both the service provider and the customer in ensuring the delivery and maintenance of the service. This may include support, maintenance, reporting, and escalation procedures.
5. Availability and Downtime: The expected availability of the service, which is often expressed as a percentage (e.g., 99% uptime). The SLA may also outline the acceptable and unacceptable periods of downtime.
6. Performance Reporting: The frequency and format of performance reports that will be provided by the service provider to the customer. These reports typically include metrics, trends, and compliance with the defined SLOs.
7. Remedies and Penalties: The actions or remedies that will be taken if the service provider fails to meet the agreed-upon service levels. This may include service credits, penalties, or other forms of compensation.