SLI vs SLO vs SLA

By Pradyumna Chippigiri

January 31, 2026

Simplest explanation of the 3 confusing terms in SRE :

Imagine we run a food delivery app like Zomato or Swiggy.

• SLI = How we measure delivery performance (Is the order reaching on time?)
• SLO = Our internal target (95% of orders should bedelivered within 30 minutes)
• SLA = Our promise to customers (99% of orders will be delivered within 45 minutes, or money back)

Ez explanation

• SLI (Service Level Indicator) : The actual measurement like API success rate, page load time etc. We dont set this, we measure it, this is the actual performance of the service, and our reality.

• SLO (Service Level Objective) : Our internal goal like "99.9% of API requests should succeed". More like what we want our SLI to be.

  • Gives an error budget (how many times/how much time we can mess up): if SLO is 99.9%, you can be down for ~43 min/month

• SLA (Service Level Agreement) : Legal promise to customers with consequences.

  • "99.9% uptime or you get credits"
  • Always we should set stricter SLO than SLA (because if our SLO == SLA, then we might not meet the SLA)

So more like this :

• We design for SLO.
• We commit to SLA.
• We audit both using SLI.