Definition: What Is an SLO?

Service Level Objectives (SLOs) are goals and targets established within a Service Level Agreement (SLA). They are typically set to measure the health and performance of a service so that a provider can ensure that the quality of their services have not breached the established SLA.

SLOs cover a range of business, technical and performance metrics, such as conversion rates, availability, uptime, response time, running cost and error rates. In the context of availability and other similar metrics, SLOs are often measured in "nines" all the way up to 100%. For example, an objective for system availability can be: 90% – one 9, 99% – two 9s, 99.9% – three 9s, 99.99% – four 9s, or 99.999% – five 9s. All these metrics are directly related to service reliability and user satisfaction. And that is effectively what SLOs are for. By defining clear and measurable reliability targets, organizations can strike an ideal balance between product development and operational efficiency, culminating in a positive and rewarding end user experience.

SLO vs. SLA

SLO and SLA are important concepts in service-level management, but they differ.

The Service Level Agreement is a contractual document created by the legal and business development teams to establish the expectations and commitments between a service provider and a customer. They are composed of multiple SLOs, which are agreed between the vendor and the customer. If the service providers don’t meet these SLOs, there will be consequences such as financial penalties or service credit.

Let’s take an example to see how SLAs and SLOs are usually defined. Suppose a company offers a SaaS platform to clients and includes an SLA as part of its sales process. This SLA ensures 99.9% uptime and no more than 1 hour of response time for critical issues. It details the company’s and client’s expectations and responsibilities regarding the platform’s performance.

The company sets SLOs for uptime and response time to meet these performance targets. For instance, it may set an SLO of 99.95% uptime and a response time of 30 minutes for critical issues. These SLOs function as measurable targets for the company to work towards to meet the commitments laid out in the SLA.

SLO vs. SLI

SLO and SLI are critical components of an SLA that sets the expectations between a service provider and its customers. Although they are closely related, they serve different purposes.

We have already discussed what an SLO is. So let’s see what an SLI is. An SLI, or Service Level Indicator, is a metric that helps measure whether the system has met the SLO. Simply put, an SLO is a target, while an SLI is the metric to measure the target. Without an SLO, there can be no SLI, as there would be no specific goal to measure. And with an SLI, it is possible to know whether the SLO is being met.

Let’s take an example to understand SLI better. Say a cloud storage provider has set a 99.95% uptime goal in the SLO. To ensure the provider meets the SLO, it may use server response time, disk latency, and network latency. If the provider fails to meet the SLO, they may breach their SLA and face penalties or other consequences.

SLOs and Error Budgets

Error budgets are another concept related to SLO, that provide a margin of error for service providers to operate within. It represents the portion of downtime or errors predefined in the SLO target that has not been used or consumed yet. In other words, it is the downtime a service provider can tolerate within a specified period before violating its SLA.

For example, let’s say that a SaaS company has an SLO of 99.9% uptime and a maximum error budget of 10 minutes per month. If the service experiences downtime of 5 minutes in a given month, its error budget is now reduced to 5 minutes. If the total amount of downtime experienced in that month exceeds the 5 minutes mark, it is considered a breach of SLA.

The goal of an error budget is to ensure the reliability of the service while allowing time to innovate and release new features. By allowing a certain amount of failure, error budgets enable service providers to take risks and experiment with new ideas while maintaining high service quality.

SLOs and error budgets work hand in hand to ensure that service providers deliver high-quality services to their customers. SLOs establish the minimum level of service quality that must be maintained, while error budgets provide the margin of error necessary for service providers to experiment and innovate.

Why Are Service Level Objectives Important?

SLOs are essential because they provide a clear and measurable way to define the level of service that customers can expect from a business. Several other benefits come from SLOs.

• Improves Quality of Service: SLOs set clear targets and expectations upfront, which is important in preventing misunderstandings or disputes between service providers and their customers. If the service provider fails to meet the SLOs outlined in the SLA, it can result in penalties or other consequences. This agreement ensures the service providers stay committed to their quality and the customers get reliable services everytime.
• Optimizes Team Performance: Your DevOps and SRE teams can use the SLO targets to prioritize services that have a direct impact on customer experience and overall reliability. For example, SLOs can help team understand when to launch stablization maintenance vs. when to release a new feature. SLOs also promote automation as your teams might automate triggers and alerts to identify issues that have the potential to become critical problems, which can improve the overall performance of team.
• Promotes Innovation: In addition to ensuring a reliable services, SLOs can also be used to dictate an affordable room for unreliability through error budgets. Error budgets can be used to provide a safe cushion for your teams to experiment with new features, which can provide a greater value to your customers. Moreover, SLOs can help team switch between maintenance and innovation mode based on the available error budgets.

What Makes a Good Service Level Objective?

A good SLO is critical to the success of your business. It should be specific, measurable, attainable, relevant, and time-bound. Several key characteristics that make a good SLO, and you should carefully consider them before creating one:

• Specific: A good SLO should clearly define the objective that your teams must achieve. For example, an e-commerce site’s SLO could achieve a page load time of three seconds or less for 95% of users.
• Measurable: You and your team members should be able to collect data on whether the objective has been achieved. It means defining how to track the metrics, the tools to measure them, and the reporting line.
• Achievable. While the conditions in a good SLO can be challenging, they should always be achievable and based on the realistic abilities of your team, infrastructure, and budget. Take into account the historical data and industry benchmark while creating an SLO.
• Relevant: If what you offer in an SLO is irrelevant to customer needs, your SLO might turn your customers away. Aim to create an SLO relevant to your customers’ needs and expectations. For example, if you have a mobile app, create an SLO focusing on mobile app performance, not the overall site performance.
• Time-bound: Having a set deadline or time frame in which the SLO should be achieved will provide clarity to both your team members and your customers on what they should expect. It helps to ensure progress and shows that the objective is achieved within a reasonable timeframe.

What Are the Components of an SLO?

Now that you know what are the main characteristics of an SLO, it’s easy to deduce the key components you should keep in mind when creating SLOs:

• A specific metric to measure, such as uptime, response time, or error rate;
• A clear target for that metric, such as 99.9% uptime or a response time of less than 500ms;
• A time frame for measuring the metric, such as a month or a quarter;
• A process for monitoring and reporting on the metric, such as a dashboard or report.

How to Set and Work with SLOs?

Creating an SLO can be a complex process. However, we can break it down into four main steps that’ll help you check all the components of an SLO:

Identify the metrics

You must start by identifying the specific metrics you want to measure. These measures can be uptime, response time, or error rate. However, the metrics must be meaningful to the team members and customers and align with your business goals.

Service level objectives can be established using single metrics like batch throughput, request latency, or failures-per-second. Alternatively, SLOs can be formulated using aggregate metrics, such as the Application Performance Index (Apdex), a widely-accepted industry standard that gauges user satisfaction through an assortment of metrics.

Set targets

After you’ve identified the metrics you want to measure, set specific SLO targets for each metric. For example, you might target 99.9% uptime or a response time of less than 500ms.

Often times, you might be tempted to set it all the way up to 100%. However, this can be an overkill. Not only your customers won’t notice too much of a difference as you move closer towards the 100% target, you might inhibit innovation by increasing your target. Aim to set your SLO targets as a number of nines (e.g., 99.99%) but keep your SLOs slightly stricter than your SLAs.

Establish time frames

Next you need to define a timeframe for the SLO per day, week, or month. When selecting the timeframe, you must consider whether it is appropriate for the identified metrics and needs of your customers. For example, if you were running an e-commerce platform, you will want to set up a SLO per day. A daily SLO would allow you to closely monitor crucial metrics such as website uptime, page load times, and order processing efficiency. Anything more frequent than that could lead to unnecessary data overload and higher operational costs without significantly improving the customer experience.

Monitor the targets

Monitoring your metrics is important to ensure that you’re meeting your targets. Use tools with synthetic monitoring and infrastructure monitoring capabilities to track your performance and identify improvement areas.

Also, it’s important to remember that SLOs are not set in stone. As your business evolves and customer expectations change, you may need to adjust your SLOs. Therefore, continuously monitor your metrics and look for opportunities to improve your performance.

Who Defines SLOs?

Several teams come together when creating SLOs. While primarily meant for the engineering teams, it is only complete with input from business leaders, product owners, and customer-facing teams. Engineering teams can collaborate with business leaders, product owners, and customer-facing teams to identify the key metrics that can measure service performance.

After the stakeholders have identified the metrics, the engineering team and the business leaders can determine the appropriate target and timeframe for each metric, which is then used to lay out the backbone of the SLO. However, when setting the target and timeframe, the stakeholders must evaluate historical data, customer needs, and other relevant factors.

The engineering team can then use tools to monitor those metrics and ensure that the SLO is met. At the same time, the engineering team must ensure that the metrics are easily accessible and visualized so that every business member can use the information when needed.

So, the collective effort from all the business stakeholders defines SLOs.

SLOs Best Practices

If you are trying to find the answer to what makes a good SLO, remember SLOs must meet the intended purpose and be attainable while also managing your resources efficiently. Only attainable and realistic targets can positively impact customer satisfaction and team morale. Considering this premise, let’s look at some of the best practices you should follow when defining SLOs.

• SLOs should follow the SLA or business objective. If you define too many SLOs that don’t support a broader goal, you are doing extra work that might not produce meaningful output.
• Ensure that technical teams and business stakeholders understand the SLO and work towards the same expectations. The company will breach SLA agreements if engineers cannot meet SLO targets. Hence, all stakeholders of the business will experience the fallout.
• Prioritize your customers before defining your SLOs to make the best use of your resources. Requirements of the prioritized customers should be considered before the other customers when setting up SLOs.
• Use an SLO monitoring tool to track and measure SLO compliance. SLO monitoring tools raise alerts whenever your SLOs are violated. They could even alert you if there is a potential for SLO breach. Such alerts can provide the context necessary for troubleshooting and also help you estimate the actual performance of your service against your SLO targets in real time. SLOs monitoring tools can provide visibility into your service health and help you identify and fix issues before they impact your customers.
• Frequent evaluation of your SLOs is crucial to identify whether they are still relevant and achievable or need adjustment. This can help you avoid situations where you’re trying to achieve SLO targets that are no longer relevant or unachievable. You must adjust your SLOs to fit your team’s and customers’ needs.

How to Monitor SLOs?

To effectively monitor SLOs, a structured approach is crucial. Here’s how you can start:

• Set up monitoring tools: Once the SLOs are established, it is essential to set up monitoring tools and systems that align with your needs, such as Synthetics for website performance monitoring and Sematext Monitoring for infrastructure monitoring. These tools allow continuous and real-time monitoring of key performance indicators (KPIs) to ensure that service levels are being met.
• Establish data collection: To monitor SLOs effectively, a robust data collection process must be in place. This involves gathering data from various sources, such as server logs, user interactions, and application performance metrics. The data collection process should be automated to ensure a consistent and reliable flow of information.
• Analyze data: Once the data is collected, it needs to be regularly analyzed to assess the performance of the services against the defined SLOs. Data analysis involves identifying trends, patterns, and potential issues that may impact service quality. For instance, analyzing response times over different time periods can help identify peak usage times and performance degradation.
• Report on performance: Reporting on SLO performance is essential to keep stakeholders informed about the status of service levels. Regular reports should be generated and shared with relevant teams and management. These reports should highlight the achievements, areas of improvement, and any deviations from the SLOs. Transparent reporting fosters accountability and facilitates data-driven decision-making.
• Review and update SLOs: SLOs should be periodically reviewed and updated. Regularly assessing the relevance of existing SLOs ensures that they remain aligned with changing business priorities and customer expectations. Additionally, feedback from customers and insights from data analysis should be used to optimize SLOs and make them more meaningful and impactful.

SLOs Monitoring with Sematext

Sematext combines the power of synthetic monitoring and infrastructure monitoring to give you a single comprehensive solution for monitoring your service level objectives. This integrated approach makes it easier for you to you create and maintain precise SLOs while delivering exceptional service to your clients.

Sematext Monitoring, the infrastructure monitoring tool, will help you define robust SLOs and get valuable visibility into the health and performance of your underlying IT infrastructure, including servers, networks, and databases. You can then use Synthetics to monitor the websites tied to your SLAs by creating dedicated monitors and specifying the relevant URLs. Built-in metrics such as response time and service availability provide essential insights for evaluating and maintaining your SLOs.

Start the 14-day free trial to explore all these SLO monitoring and see how they empowers you to achieve and exceed your SLOs with confidence.

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