Reliability Targets Discussion Language
5 exercises — Practice the English for negotiating SLO targets with stakeholders, calibrating based on consequences, and bootstrapping first SLOs.
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A product team requests 99.99% availability for their new feature. The SRE lead responds: "Before we commit to that, let's talk about what that actually means and whether it's justified." Which statement correctly frames the conversation?
Setting reliability targets is a cost-benefit negotiation, not a technical exercise alone.
The downtime math makes the cost tangible:
• 99% = 3.65 days/year
• 99.9% = 8.76 hours/year
• 99.99% = 52.6 minutes/year
• 99.999% = 5.26 minutes/year
Each additional "nine" is exponentially more expensive to achieve — it requires more redundancy, more operational complexity, more testing.
The right question: "What are the actual consequences of downtime for this service?" A blog doesn't need 99.99%. A payment processor might.
Key vocabulary:
• Nines of availability — colloquial term for the number of 9s in the availability percentage
• Cost of reliability — engineering and infrastructure investment required to achieve a target
• Justified reliability — the highest SLO whose cost is warranted by business impact
• Single point of failure — a component whose failure brings down the whole service
The downtime math makes the cost tangible:
• 99% = 3.65 days/year
• 99.9% = 8.76 hours/year
• 99.99% = 52.6 minutes/year
• 99.999% = 5.26 minutes/year
Each additional "nine" is exponentially more expensive to achieve — it requires more redundancy, more operational complexity, more testing.
The right question: "What are the actual consequences of downtime for this service?" A blog doesn't need 99.99%. A payment processor might.
Key vocabulary:
• Nines of availability — colloquial term for the number of 9s in the availability percentage
• Cost of reliability — engineering and infrastructure investment required to achieve a target
• Justified reliability — the highest SLO whose cost is warranted by business impact
• Single point of failure — a component whose failure brings down the whole service