In today’s technology-driven world, where the expectations of users are high, it is essential for companies to understand and maintain SLAs, SLOs, and SLIs. These three initialisms represent the promises made to users, the internal objectives that help meet those promises and the trackable measurements that indicate performance. By aligning everyone involved, including vendors and clients, on system performance, companies can deliver the speed, uptime, and functionality that users expect.

Service Level Agreements (SLAs)

A Service Level Agreement (SLA) is an agreement between a provider and a client that outlines measurable metrics such as uptime, responsiveness, and responsibilities. SLAs are usually drafted by a company’s new business and legal teams, and they represent the promises made to customers. In case of failure to meet these promises, there are often consequences, such as financial penalties, service credits, or license extensions.

However, SLAs can be challenging to measure, report on, and meet. They often make promises that are difficult to measure and don’t align with evolving business priorities. Additionally, they may not account for factors outside the provider’s control, such as delays caused by the client. To address these challenges, it is crucial for tech and DevOps teams to collaborate with legal and business development to create SLAs that address real-world scenarios.

SLAs are typically necessary for paying customers, as they establish the terms of the service agreement between the vendor and the customer.

Service Level Objectives (SLOs)

Service Level Objectives (SLOs) are agreements within SLAs that define specific metrics such as uptime or response time. While SLAs represent the overall agreement between the provider and the customer, SLOs are the individual promises made to the customer. SLOs set customer expectations and guide IT and DevOps teams in determining their goals and measuring their performance.

To ensure effective use of SLOs, it is crucial to keep them simple, clear, and focused on the metrics that matter most to customers. Avoiding complexity and tracking only essential metrics will prevent confusion and make it easier for engineers to meet the objectives.

SLOs can be relevant for both paid and unpaid accounts, as well as internal and external customers. Internal systems, such as CRMs and intranets, are just as important as external-facing systems, and having SLOs for internal systems enables teams to meet their own customer-facing goals.

Service Level Indicators (SLIs)

Service Level Indicators (SLIs) measure compliance with SLOs. They are the actual measurements of performance against the defined objectives. For example, if the SLA specifies that systems should be available 99.95% of the time, the SLO would likely be 99.95% uptime, and the SLI would measure the actual uptime achieved. To remain in compliance with the SLA, the SLI must meet or exceed the promises made in the agreement.

Like SLOs, the challenge with SLIs lies in keeping them simple and focused on the metrics that truly matter. Tracking too many metrics that are not relevant to clients can complicate the job of IT teams. Therefore, it is essential to choose the right metrics and avoid overcomplicating the measurement process.

Companies measuring their performance against SLOs need SLIs to accurately measure and evaluate their progress. SLIs are an integral part of the performance-tracking process and enable companies to assess their adherence to the agreed-upon objectives.

Best Practices for SLAs, SLOs, and SLIs

To ensure the effectiveness of SLAs, SLOs, and SLIs, it is important to follow these best practices:

Craft SLAs Around Customer Expectations

When creating SLAs, it is important to focus on what matters most to the customer. Avoid overcomplicating the agreements by making promises for each individual component of the system. Instead, confine the promises to high-level, user-facing functionality. This approach simplifies the lives of IT professionals responsible for meeting the SLA promises and reduces confusion for clients.

Use Plain Language in SLAs

The language used in SLAs should be simple and easily understood by clients. Complicated language can lead to misunderstandings and conflicts. By using plain language, companies can ensure that clients have a clear understanding of the terms and expectations outlined in the SLA.

Less is More with SLOs

Not every metric is critical to client success, so it is important to commit to as few SLOs as possible. Focus on the metrics that have the most significant impact on customers and avoid overwhelming IT and DevOps teams with unnecessary objectives. By prioritizing the most important metrics, teams can concentrate their efforts on meeting the goals that truly matter to clients.

Select Metrics Carefully for SLIs

Similar to SLOs, it is important to strategically choose the metrics that will be tracked as SLIs. Tracking too many metrics can quickly become unwieldy and distract from the core objectives. By selecting the most relevant and impactful metrics, companies can effectively measure and evaluate their performance against SLOs without overwhelming IT teams.

Consider Factors Outside of IT Control

SLAs should account for factors outside of the IT team’s control, such as client-side delays. It is important to clarify how these factors will be managed and resolved in the SLA. By addressing these considerations upfront, companies can avoid setting unrealistic expectations and ensure that their teams are not held accountable for issues beyond their control.

Build in an Error Budget

Including an error budget in SLAs and SLOs provides room for failures and unforeseen issues. An error budget protects against SLA violations and allows for agility in making changes and trying innovative solutions. It also enables companies to identify potential issues and maintain appropriate expectations with clients. Google even suggests using leftover error budget for planned downtime to identify any unforeseen issues.

Set Realistic Goals

It is crucial to set realistic and achievable goals for SLOs. While it may be possible for a team to maintain 99.99% uptime, it is better to under-promise and overdeliver. This approach is particularly suitable for agile teams that aim to launch early and often. By setting realistic goals, teams can maintain an error budget and keep up with the fast pace of development.

Impact on Site Reliability Engineering (SREs)

For organizations implementing Site Reliability Engineering (SRE) teams, SLAs, SLOs, and SLIs are fundamental to success. SLAs help establish boundaries and error budgets, while SLOs help prioritize work. SLIs inform SREs when to halt launches to protect the error budget and when to proceed. By effectively managing SLAs, SLOs, and SLIs, SRE teams can ensure the reliability and performance of their systems.


Understanding the differences between SLAs, SLOs, and SLIs is crucial for technology companies to meet user expectations and deliver high-quality services. SLAs establish measurable metrics and agreements between providers and clients, while SLOs define specific objectives within SLAs. SLIs measure compliance with SLOs and provide insights into performance.

By following best practices such as aligning SLAs with customer expectations, using plain language, and focusing on essential metrics, companies can effectively manage SLAs, SLOs, and SLIs. Additionally, considering factors outside of IT control, building error budgets, setting realistic goals, and leveraging the concepts in Site Reliability Engineering enable organizations to meet their performance objectives and ensure customer satisfaction.

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