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SLA (Service Level Agreement)

A contract that defines the level of service a provider commits to deliver, including measures such as uptime and response times, and the penalties if those levels are not met.

What is an SLA?

A Service Level Agreement (SLA) is a contract that defines the level of service a provider commits to deliver, including measures such as uptime, availability, and response times. It sets clear, measurable expectations between a provider and a customer and spells out what happens if the agreed levels are not met. For IT and managed services, the SLA is the benchmark by which performance is measured and the provider is held accountable.

What does an SLA typically include?

Services covered: Exactly what is included, and often what is excluded, to avoid confusion.
Performance metrics: Measurable targets such as uptime percentage, response time, and resolution time.
Roles and responsibilities: Who is responsible for what, and where handoffs happen.
Penalties and remedies: What the customer receives if targets are missed, usually service credits or fee reductions.
Exclusions: Situations that do not count against the SLA, such as scheduled maintenance.

What are common SLA metrics?

Uptime and availability: Often expressed as a percentage, for example 99.9 percent, which allows roughly 43 minutes of downtime per month.
Response time: How quickly the provider acknowledges a logged issue.
Resolution time: How quickly an issue is fixed once reported.
Error and defect rates: Limits on failures and quality problems.

How do SLA, SLO, and SLI relate?

SLA: The external contract and the promises made to the customer.
SLO (Service Level Objective): An internal target the provider sets in order to meet the SLA, such as 99.95 percent uptime.
SLI (Service Level Indicator): The actual measured value, which must meet or beat the SLO to keep the SLA satisfied.

Why do SLAs matter?

Accountability: Predefined consequences create real accountability when something goes wrong.
Confidence: Customers know critical systems will be supported to a defined standard.
Benchmark for managed services: For a NOC or managed provider, the SLA is the yardstick that proves round-the-clock coverage is actually being delivered.