Do you know the differences between SLA, SLO and SLI?

tl;dr 😎

SLA

A Service Level Agreement are the promises we give to our clients for reaching our goals (SLOs).

SLO

A Service Level Objective are the goals we want to achieve.

SLI

A Service Level Indicator is the way we measure whether we meet our goals (SLO) or not.

And the bit longer version… 😅

There is one common thing between all tech companies – they provide a service.
No matter if it’s free of charge or a paid one, in the end – customers interact with your services and expect them to be available for them all the time (or should they?).

On the other hand, companies thrive to provide the best user experience (not just UX per se) by having faster APIs, better uptime, and fewer connection errors – or in other words, reliability.

Reliability planner

A well defined SLOs are a great tool for reducing the amount of annoying alerts by focusing on a strong ground set of alerts toward customer facing pain points (SLO breach).

As a best practice, it’s good to start with defining the SLOs goals of your services.
SLOs are not just technical objectives but also operational objectives and it’s important to harness both the business and the engineering sides when defining those.

Less is more

You should not define SLOs for every metric you have in your system – aim toward customer facing issues only.

Your SLOs should be clear and easy to understand, don’t use fancy words and vague meanings when defining them – you need to remember that many engineers interact with them at different seniority levels during their daily work and on-call routine.

The numbers

SLOs must be of the measureable kind that you can alert on

Once you have your SLOs in place, it’s time to set the SLIs – the way we measure if we are meeting our goals (SLOs) or not and set alerts based on them.

So in other words, when we set a goal (SLO) of having our services available at 99.999% the way we measure it will be defined as SLI so we can later promise it (SLA) to our customers when an agreement.

Promises

Not all service consumers are entitled to a SLA

The last bit of the trinity is the SLA – our agreement as a service provider with our customers.

It’s very important to have this process a co-venture of both the legal and the engineering teams.

By that, you cover the legal issues and aspects on what is right and wrong and how to protect the company.

And on the other hand, you cover the engineering aspect – not letting the legal team (and product) to promise mountains and hills to customers at the expense of your mental health.