I have seen these two abbreviations being used interchangeably. Also, I have seen SLA being used as a catch all term for anything related to 'what the test is supposed to measure and compare against'. SLO looks like a new entrant and is being used in web performance testing specifically. My questions are: What exactly is an SLO? How does it differ from SLA? From a performance testing point of view, how should these terms be used?

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Service-level agreement

A service-level agreement is an agreement between two or more parties, where one is the customer and the others are service providers. This can be a legally binding formal or an informal "contract" (for example, internal department relationships).

The agreement may involve separate organizations, or different teams within one organization

Contracts between the service provider and other third parties are often (incorrectly) called SLAs – because the level of service has been set by the (principal) customer, there can be no "agreement" between third parties; these agreements are simply "contracts." Operational-level agreements or OLAs, however, may be used by internal groups to support SLAs. If some aspect of a service has not been agreed with the customer, it is not an "SLA".

Customer Based SLA - An agreement with an individual customer group, covering all the services they use. For example, an SLA between a supplier (IT service provider) and the finance department of a large organization for the services such as finance system, payroll system, billing system, procurement/purchase system, etc.

Service Based SLA - An agreement for all customers using the services being delivered by the service provider

Multilevel SLA - The SLA is split into the different levels, each addressing different set of customers for the same services, in the same SLA.

  1. Corporate-level SLA

  2. Customer-level SLA

  3. Service-level SLA

Service-level objectives (SLO)

A service level objective (SLO) is a key element of a service level agreement (SLA) between a service provider and a customer. SLOs are agreed as a means of measuring the performance of the Service Provider and are outlined as a way of avoiding disputes between the two parties based on misunderstanding.

There is often confusion in the use of SLA and SLO. The SLA is the entire agreement that specifies what service is to be provided, how it is supported, times, locations, costs, performance, and responsibilities of the parties involved. SLOs are specific measurable characteristics of the SLA such as availability, throughput, frequency, response time, or quality.

from Service Level Objective, Wikipedia

A service level objective (SLO) is a key element of a service level agreement (SLA) between a service provider and a customer. SLOs are agreed as a means of measuring the performance of the Service Provider and are outlined as a way of avoiding disputes between the two parties based on misunderstanding.

Service level agreement(SLA)

A written agreement documenting the required levels of service. The SLA is agreed on by the IT service provider and the business, or the IT service provider and a third-party provider. A service-level agreement (SLA) is a contractual agreement outlining a specific service commitment made between contract parties -- a service provider and its customer

Service-level objectives (SLO)

Each SLO corresponds with a single performance characteristic relevant to the delivery of an overall service. Some examples of SLOs would include: system availability, help desk incident resolution time and application response time. A service level objective (SLO) is a key element of a service level agreement (SLA) between a service provider and a customer.

SLOs are agreed as a means of measuring the performance of the Service Provider SLOs are outlined as a way of avoiding disputes between the two parties based on misunderstanding The SLA is the entire agreement that specifies what service is to be provided SLOs are specific measurable characteristics of the SLA such as availability, throughput, frequency, response time, or quality. The term SLO is deprecated in ITIL V3 to Service Level Target

This topic is actually well discussed, please follow the links below:

Differences between SLA and SLO

SLA and SLO discussion on Quora

SLA on Wikipedia

SLO on Wikipedia

In one sentence, SLO is part of SLA. SLA is a legal contract while SLO has some specific definitions regarding performances, which can be used to guide performance testings.

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