Explain like I'm five · SRE

What is an SLA?

A Service Level Agreement, told as a story about putting the promise on paper, officially, with a customer.

what did our contract promise us?CONTRACTthere's nothing herea big customer asks, but there's no document

A big customer asks, but there's no document.A target kept to ourselves can't reassure the customer.

OUR OWN TARGET (SLO)target: 99.9%nobody outside knowswhat happens if you miss it?um... well...a target kept to ourselves can't reassure the customer

Why is this hard?There's nothing written down for what happens if it's missed.

SLA CONTRACTpromise: 99.9% or highermiss it: refund 10% of the feereported every quarterput the promise on paper, officially, with the customerlooser than the internal target, and it spells out what happens if we miss

Put the promise on paper, officially, with the customer.It spells out what happens if we miss, too.

Looser than the internal targetleaves room to breathe
Set the payback for missing ita refund or a credit
A different contract per customerthey don't have to match
Report it every quarterso they know it was kept
CONTRACT DETAILSpromise: 99.9%+miss it: 10% refundreport: quarterlyeach customer has its own contractSIGNEDManager (signed)it spells out the percentage and what happens if it's missed

It spells out the percentage and what happens if it's missed.Once the manager signs, it becomes an official contract.

INTERNAL (SLO)99.95%CUSTOMER (SLA)99.9%there's a buffer between themINTERNAL (SLO)99.9%CUSTOMER (SLA)99.9%no buffer at allpenaltythe contract has to be looser than the internal target to stay safe

The contract has to be looser than the internal target to stay safe.Set them equally tight, and the smallest miss triggers a penalty.

In one breath

An SLA is the promise put on paper, officially, with a customer — set looser than the internal SLO, and spelling out what gets paid back if it's missed.

Usually a legally binding document spelling out an uptime clause and the credits or refunds owed on a breach. Set it as tight as the internal SLO, and the smallest wobble triggers a penalty.

When grown-ups say it

SLA
The promise made official with a customer. A legally binding document.
SLA vs SLO
What's kept internal versus promised outward. The SLA is usually looser than the SLO. → the target line set internally
Penalty / credit
What's paid back when it's missed. Often a refund or a service credit.
Compliance report
The document that shows whether the promise held. Usually sent every quarter.
Measurement dispute
A fight over whose numbers are right. That's why the contract spells out how it's measured, too.
Per-customer terms
Terms that can differ customer to customer. The bigger the customer, the more detailed it gets.
Legal binding
Breaking the promise carries real consequences. That's why it's written down, not just spoken.
Uptime clause
The line that spells out how much uptime is owed. This clause is the heart of the contract.
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