99.9 vs 99.99 Uptime
A practical reliability guide for founders and operators.
99.9 vs 99.99 Uptime from Sandglass: practical guidance for understanding the operational cost of moving from hours of allowed downtime to minutes.
What this guide covers
This guide focuses on understanding the operational cost of moving from hours of allowed downtime to minutes. The goal is to make the operating decision clear before a stressful incident forces the team to improvise.
- 99.9% allows minutes per day; 99.99% allows seconds.
- The extra nine is paid for in redundancy and detection speed.
- A dependency you do not control caps the target you can promise.
How Sandglass supports the practice
Compare the downtime budget, incident response speed, deploy process, and dependency risk before choosing a target. Sandglass supports the continuous side of this work with checks, incidents, alert routing, and public status visibility.
- Back the practices here with HTTP, ping, TCP, content, SSL certificate, and heartbeat checks.
- Route incidents to email, Slack webhook channels, and generic webhooks so the right people respond fast.
- Use a public status page to keep customers informed while the team works the incident.
Common mistakes to avoid
Higher uptime targets are expensive because they require redundancy, faster detection, and disciplined operations, not just a stricter monitor.
Implementation checklist
Step 1: Start from customer impact
Decide which failures in this topic actually reach customers before adding any monitoring.
Step 2: Choose one signal per risk
Match each risk to a single HTTP, content, TCP, SSL certificate, or heartbeat check instead of stacking duplicates.
Step 3: Assign an owner and a channel
Give each alert one owner and one destination — email, a Slack webhook, or a generic webhook.
Step 4: Review after real incidents
Revisit intervals, thresholds, and ownership once a real incident shows what was missing.