Uptime and Availability Glossary
Clear definitions for all monitoring terminology.
Monitoring comes with its own vocabulary. Understanding these terms is essential for effective communication.
This glossary covers the most common terms in uptime monitoring and availability management.
Use it as a reference when discussing SLAs, incidents, or monitoring strategies.
Disponibilité de Base
- Uptime
- Temps pendant lequel un service est opérationnel et accessible. Opposé de downtime.
- Downtime
- Temps pendant lequel un service est indisponible ou non fonctionnel.
- Availability (Disponibilité)
- Pourcentage de temps où le service est opérationnel. Uptime / (Uptime + Downtime) × 100.
- Nines (Les "neuf")
- Façon d'exprimer la disponibilité. 99.9% = "trois nines", 99.99% = "quatre nines".
SLA, SLO, SLI
- SLA (Service Level Agreement)
- Contrat définissant le niveau de service promis au client, avec pénalités en cas de non-respect.
- SLO (Service Level Objective)
- Objectif interne de niveau de service. Plus strict que le SLA pour avoir une marge.
- SLI (Service Level Indicator)
- Métrique mesurant le niveau de service. Ex: pourcentage de requêtes < 200ms.
- Error Budget
- Quantité de downtime "autorisé" par le SLO. 99.9% SLO = 0.1% d'error budget.
Métriques de Fiabilité
- MTTR (Mean Time To Recover)
- Temps moyen entre la détection d'un incident et sa résolution.
- MTTD (Mean Time To Detect)
- Temps moyen entre le début d'un incident et sa détection.
- MTBF (Mean Time Between Failures)
- Temps moyen entre deux incidents. Mesure de la fiabilité globale.
- MTTA (Mean Time To Acknowledge)
- Temps moyen entre la réception d'une alerte et sa prise en charge.
Frequently Asked Questions
What's the difference between uptime and availability?
Often used interchangeably. Technically, availability = uptime / total time, expressed as percentage.
How do I calculate downtime from availability?
(1 - availability) × time period. For 99.9% monthly: 0.001 × 30 days × 24h = 43 min downtime.
Is 99.9% uptime good enough?
Depends on your business. 99.9% means ~8.7 hours/year downtime. E-commerce may need higher.
What's a typical MTTD for good monitoring?
With proper monitoring like MoniTao, MTTD can be under 1 minute for HTTP checks.
Speak the Language
Understanding these terms helps you communicate with your team, vendors, and stakeholders.
MoniTao helps you improve all these metrics: reduce MTTD, increase uptime, meet your SLOs.
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