🛡️High Availability

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Also known as: HA

A system property achieved through redundancy and resilience strategies to minimize downtime and meet target uptime objectives.

DESCRIPTION

High availability (HA) designs eliminate single points of failure using redundancy, replication, and automatic failover. They rely on health checks, load balancing, and capacity planning to withstand component failures. HA is measured against service-level objectives and often expressed as “nines” of uptime. It complements disaster recovery for regional failures. Observability and testing are vital to verify resilience in real incidents.

ALTERNATIVE DEFINITIONS

Wikipedia

High availability is a characteristic of a system which aims to ensure an agreed level of operational performance, usually uptime, for a higher than normal period.

Links HA to uptime objectives as performance over time.

Source

AWS Well-Architected

High availability is achieved by designing systems that can recover from infrastructure or service disruptions and dynamically acquire computing resources to meet demand.

Emphasizes design principles for resilience in the cloud.

Source

RELATED TERMS

Durability (ACID) Failover Data Redundancy Cluster Analysis Replication Load Balancing Service Level Objective Disaster Recovery

COMPETING TERMS

Single Point of Failure

RELATIONS

• Broader: Availability

KNOWLEDGE AREAS

Infrastructure Cloud Data Architecture Observability & Telemetry

TARGET AUDIENCE

Cloud Architect DevOps Engineer IT Manager Solution Architect Chief Technology Officer

EXTERNAL SOURCES

• Wikipedia - High availability
• Google Cloud - Reliability pillar for HA design
• Microsoft Learn - Azure availability design patterns
• Google SRE - SLOs and availability targets

TOP QUESTIONS

How is High Availability measured?

By uptime against SLOs, typically expressed as nines, e.g., 99.9% or 99.99% availability.

Category: Requirements

What patterns enable High Availability?

Redundancy, replication, stateless scaling, load balancing, graceful degradation, and automated failover are common patterns.

Category: Example

What is the biggest misconception about High Availability?

That it eliminates downtime entirely. HA reduces downtime but doesn’t guarantee zero downtime.

Category: Misunderstanding

How does High Availability relate to Disaster Recovery?

HA addresses component failures and short outages; DR handles large-scale or regional failures with different RTO/RPO goals.

Category: Example

What are common HA mistakes?

Hidden single points of failure, insufficient capacity, and untested automation can undermine availability.

Category: Mistakes

What’s a hot topic in High Availability today?

Multi-region active-active architectures and chaos engineering to validate resilience are trending.

Category: Topic

How does observability support High Availability?

Metrics, logs, and traces reveal early degradation and guide automated remediation and scaling.

Category: Management

What role do SLOs play in HA?

They define acceptable risk and guide engineering trade-offs in redundancy and cost.

Category: Management

Is High Availability expensive?

It adds cost via redundancy and complexity, but often costs less than downtime for critical services.

Category: Opinion