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SLO — Service-Level Objectives

What is an SLO?

An industry analyst firm defines Service-Level Objectives (SLOs) broadly as agreed-upon service performance goals or SLO targets within a Service Level Agreement (SLA) that must be achieved for each service activity, function, and process to provide the best opportunity for recipient (end user) success.

In other words, SLOs represent the performance of a service as determined by a set of SLO targets and their target values. Examples of measured metrics include service uptime, response time, or request latency.

Who needs SLOs?

If you view the overall SLA as the formal agreement that specifies aspects, such as service performance, how it is supported, and the relevant parties' responsibilities, then SLOs are the specific, measurable characteristics of the SLA.

Where SLAs are more appropriate in the case of formal contracts with external providers, SLOs can also be applied to assist in quantifying performance internally.

Internal systems, such as CRMs, client data repositories, and intranet, can be just as crucial as external-facing systems. Embracing SLOs for internal systems is essential to meeting business goals and enabling internal teams to meet their own customer-facing user experience goals.

How do SLOs work?

SLOs aim to deliver more reliable, resilient, and responsive services that meet user expectations. Reliability and responsiveness are often measured in terms of percentages that are less than but very close to 100% (e.g., 99% or 99.99% availability). 99.999% availability is referred to as “5 nines“ availability and indicates that a service is inaccessible to a user for only 5 minutes a year. They represent aggregate goals that are backed up typically by real-time performance measurements.

The metrics used to measure SLO compliance are called Service Level Indicators (SLIs). SLI metrics indicate whether or not an organization is meeting SLO targets. SLIs are also used to determine alerting policies when SLO targets do not comply with a specified range in real-time and if notifications are required.

Gathering and analyzing representative metrics over time will help Site Reliability Engineering (SRE) or DevOps staff determine the effectiveness of SLOs so they can more directly assess business impacts.

SLO vs. SLA

Google distinguishes between an SLO and an SLA as follows:

  • Service Level Objectives (SLOs) are the targeted service levels typically expressed as a percentage of availability over some time.
  • Service Level Agreements (SLAs) are formal agreements that outline the level of service enterprises can expect from service providers. If these promises are not met, the provider can have significant consequences, often financial reimbursements.

An SLA typically involves an assurance made by a service provider to an enterprise customer using a service, such as those offered by an ISP that provides Internet connectivity, and should meet a certain level of availability over a designated time period. If it fails, then some penalty will be paid to the enterprise customer. The penalty is typically in the form of service credits. 

SLOs are similar to SLAs but explicitly refer to the performance or reliability targets as specific metric values agreed to internally within an enterprise.

SLO Monitoring Solution

Cloud-native applications rely on many components and dependencies, making SLO compliance challenging to track. ThousandEyes can be crucial in identifying the elements involved in the service delivery chain, providing visibility into key metrics that can be used to formulate meaningful SLIs, which can then subsequently be monitored to assure SLO compliance. 

To understand how employees or customers experience an application and the impact of every network and service on performance, modern synthetics paired with deep network path and routing visualization are a central requirement.

ThousandEyes Browser Synthetics emulates user interactions with a website or application. Detailed page metrics and waterfalls are tightly correlated with underlying network and Internet issues to help your organization quickly isolate the most probable cause of application downtime, including third-party API  dependencies.

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