High Availability (HA)
High Availability
System design ensuring services remain operational for a very high percentage of time (99.9%+), minimising downtime through redundancy, failover, and fault tolerance.
In-Depth Explanation
High Availability (HA) refers to systems designed for minimal downtime, measured as a percentage:
- 99%: 3.65 days downtime/year
- 99.9%: 8.76 hours downtime/year
- 99.99%: 52.6 minutes downtime/year
- 99.999%: 5.26 minutes downtime/year
HA design principles:
- Redundancy: No single point of failure
- Failover: Automatic switching to backups
- Load balancing: Distributing traffic across instances
- Health checks: Continuous monitoring
- Graceful degradation: Maintaining core functionality during partial failures
Implementation patterns:
- Active-active: Multiple instances handle traffic simultaneously
- Active-passive: Primary with standby failover
- Multi-AZ: Instances across availability zones
- Database replication: Primary with synchronous replicas
- Stateless design: No session state on individual servers
- Circuit breakers: Preventing cascading failures
Cloud HA services:
- Load balancers: AWS ALB, Azure LB, GCP Load Balancing
- Managed databases: RDS Multi-AZ, Cloud SQL HA
- Container orchestration: Kubernetes with auto-healing
- DNS failover: Route 53 health checks
Cost scales exponentially with each additional "nine." Choose based on business cost of downtime.
Business Context
High availability directly impacts revenue and reputation. Every minute of downtime for an e-commerce site translates to lost sales and customer trust.
How Clever Ops Uses This
Clever Ops architects high-availability solutions for Australian businesses, implementing redundancy, failover, and monitoring that meet specific uptime requirements.
Example Use Case
"A payment platform achieves 99.99% uptime by deploying across 3 AZs with active-active configuration and automated failover, limiting annual downtime to under 53 minutes."