What are SLIs, SLOs, and SLAs?
SLIs, SLOs, and SLAs are all important terms in the world of service-level management for Site Reliability Engineers and Business teams alike. They are all interrelated, but they each have a different purpose.
SLI stands for Service Level Indicator (basically metrics). These are the metrics that are used to measure the performance of a service. For example, an SLI might be latency, RPS, etc.
SLO stands for Service Level Objective. It is a target value for an SLI (basically, what are the limits for my metrics). For example, an SLO might be that the website should be able to process 100 requests per second.
SLA stands for Service Level Agreement. It is a contract between a service provider and a customer that specifies the level of service that the customer can expect to receive. The SLA will typically include the SLOs that the service provider is committed to meeting. So when AWS says that S3 has an SLA of 99.999999999% for durability, it means that for a period of a year, S3 is making a commitment to you that of all the data that you store in S3, 99.99...% of the objects will be available, and AWS takes the responsibility of ensuring that it meets the agreement.
\>> AWS also mentions the penalty it is liable to if the SLAs are not met
The SLI, SLO, and SLA are all important parts of service-level management. The SLI is used to measure the performance of the service, the SLO is used to set targets for the performance, and the SLA is used to communicate the level of service to the customer.
Here is an example of how SLIs, SLOs, and SLAs might be used in a real-world scenario. A company might have an SLA with its customers that guarantee 99.9% uptime. The company might then set an SLO of 99.95% uptime. To measure uptime, the company might use an SLI that measures the number of minutes that the website is unavailable each day. If the website is unavailable for more than 0.05% of the day, the company will be in breach of its SLA and will have to pay penalties to its customers.
SLIs, SLOs, and SLAs are all important tools for managing the performance of services. By understanding these terms and how they are used, you can help to ensure that your services are meeting the needs of your customers.
