What are SLA, SLO, and SLI?

Learn the differences between SLA, SLO and SLI and how to implement these metrics to improve the quality of service offered by your company. Also, learn about the challenges and best practices for implementing them, along with some real-world examples.

Importance of SLA, SLO and SLI in user experience

Talking about SLA, SLO and SLI means talking about user experience. Each of these acronyms (we will explain them later) is on the minds of developers, who are looking to achieve increasingly reliable and high-quality IT services and resources. To achieve this, they must understand and effectively manage objectives at service levels, relying on defined indicators and formal agreements that lead them to achieve user satisfaction.

Objective of metrics and their application in system performance

What is measured can be improved… so metrics help ensure a service meets its performance and reliability goals. They also help align the goals of different teams within an organization toward one goal: the best user experience.

Differences between SLA, SLO and SLI

• Definition and scope of each metric.
  Imagine a base where SLI (Service Level Indicators) refers to the quantifiable measurement to evaluate the performance of a service. Above this base you may find SLO (Service Level Objectives), which set objectives for service performance, and SLA (Service Level Agreement), which are legally binding contracts between a service provider and a customer.
• Example and applications in different contexts.
  For example, a cloud service provider may define latency as the amount of time it takes to process a user’s request and return a response as SLI. From there, an SLO of no more than 100 milliseconds is established for a consecutive period of 30 days; if the average latency exceeds this value, they will issue service credits to customers.
  If an SLI is set on the e-commerce website based on the error rate as a percentage of failed transactions, the SLO could set the error rate to not exceed 0.5% during any 24-hour period. The SLA agreed with the cloud service provider would include this SLO, along with penalties or compensation if it is not met.

SLI: Service Level Indicator

Meaning and function

Service Level Indicators (SLIs) measure the performance and reliability of a service, to determine whether an offer meets its quality objectives. The SLI also helps identify areas for improvement. Examples of indicators include latency (response time), error rate, throughput, and availability (uptime). These metrics are usually monitored over specific time periods to assess performance. As it can be seen, SLIs are the foundation for setting performance and reliability benchmarks for a service.

Challenges and strategies for their measurement

Based on the fact that SLI refers to metrics, the main challenge is to achieve a simple approach to the indicators, since they must be easily analyzed and compared in order to speed up decision-making based on the results. Another challenge is choosing useful tracking metrics that correspond to the actual needs of the product or service.

SLO: Service Level Objective

Definition and purpose

Service Level Objectives (SLOs) set performance and reliability objectives that service providers aim to achieve, in line with a service’s SLIs. So these SLO help to evaluate and monitor whether the service meets the desired quality level. For example, a cloud provider may say that their goal is to achieve 99.99% availability over a specific time period.

Challenges and recommendations for implementation

The main challenge is that objectives must be clear, specific and measurable, so it is recommended that the service provider works closely with stakeholders to define SLOs and their scopes.

SLA: Service Level Agreement

Concept and purpose

A service level agreement (SLA) is a legally binding contract between a service provider and a customer, outlining agreed SLOs and penalties for non-compliance. SLAs ensure that providers and stakeholders clearly understand the expectations about the quality of service and the repercussions in case of non-compliance (financial compensation or service credits) with the agreed standards. SLAs include SLOs such as latency times, error rate, and availability. Of course, before service begins, the service provider and the customer will negotiate Service Level Agreements. SLAs help to have a clear understanding of performance expectations, channels and courses of action, and service reliability, safeguarding the interests of both parties.

Challenges and best practices

One of the most important challenges of an SLA is that it does not go along the line of business priorities, so a best practice is to involve the business areas where the greatest impact on the service level is generated in the agreements. Also, monitoring the SLA and updating them can be a complex process that requires reports with data obtained from multiple sources of information. In this regard, it is recommended to acquire the technological tools that help to retrieve data from multiple sources in a more agile and automated way.

Comparison between SLA, SLO and SLI

As we have seen, SLIs are the foundation for SLOs and SLAs, with quantitative metrics to assess service performance and reliability. SLOs use data derived from SLIs to set specific objectives on service performance, ensuring that the service provider and stakeholders have clear objectives to achieve. Hence, SLAs incorporate SLOs into a contract between the service provider and the customer, so that both parties have a clear understanding of performance expectations and consequences in the event of non-compliance.
To be clearer, it helps to look at these tables that compare differences, challenges, and best practices:

Table 1: Differences between SLA, SLO and SLI

Metric	Purpose	Application	Flexibility
SLI	Actual measurement of service performance.	Internal, paid. (actual number on performance)	High flexibility.
SLO	Internal objectives that indicate service performance.	Internal and external, free and paid. (objectives of the internal team to comply with the service level agreement)	Moderate flexibility.
SLA	Agreement with customers on service commitments.	Payments, availability. (the agreement between the provider and the service user)	Low flexibility.

As it can be seen in Table 1, to the extent that the metric is more specific (SLI), there is greater flexibility for its definition, AND, the more specific the metric (SLA), the more parties involved the commitment is.

Table 2: Challenges and best practices

Metric	Challenges	Best Practices
SLI	Definition of product or service associated with business needs. Accurate and consistent measurement.	Another challenge is choosing useful tracking metrics that correspond to the actual needs of the product or service. Track system evolution and visualize data.
SLO	Balance between complexity and simplicity. Define the objectives must be clear, specific and measurable.	Close collaboration with the parties involved in the service to define SLOs and their scopes. Continuously improve and select valuable metrics.
SLA	Alignment with business objectives. Collaboration between legal and technical teams. Retrieving data from multiple sources to measure compliance levels.	Define realistic expectations, with a clear understanding of the impact on the business. Reach consensus with stakeholders and the technical team to define the agreements in the SLA. Use technological tools that help to retrieve data from multiple sources in a more agile and automated way.

In Table 2, you may see that the challenges for the metric are different, due to their internal or external nature. For example, SLOs are internal objectives of the service provider, while SLAs establish a commitment between the provider and the customer (service user), as well as penalties in case of non-compliance.

Real-world applications

Examples of how these metrics are applied in different companies and services.

• SLI:
  • Service availability/uptime.
  • Number of successful transactions/service requests.
  • Data consistency.
• SLO:
  • Disk life must be 99.9%
  • Service availability must be 99.5%
  • Requests/transactions successfully served must reach 99.999%
• SLA:
  • Agreement with clauses and declarations of the signing parties (supplier and user), validity of the agreement, description of services and their corresponding metrics, contact details and hours for support and escalation courses, sanctions and causes of termination in case of non-compliance, termination clauses, among others.

Conclusion

Service metrics are essential to ensure the quality of the service offered. Whether you are working with the service provider or you are on the other side of the desk, the service user, you need to have reliable and clear information about a service’s performance in order to generate better user experiences, which in turn translates into better responsiveness to internal customers (including vendors and business partners) and external customers of any organization. Additionally, do not overlook the fact that more and more companies are adopting outsourcing services, so it is helpful to be familiar with these terms, their applicability and best practices.

We also recommend these tools that Pandora FMS puts at your disposal:

• Powerful SLA Reports (by days, hours, weeks).
• Pandora FMS Uptime calculator, which measures online time of a machine or server, available status and service time.