High Availability
Definition
High availability describes the ability of a system to remain available with minimal interruption despite failures.
Depending on the system, measures such as redundancy, failover, replication, health checks, and robust operational processes contribute to high availability. A single percentage value without a measurement window and SLA context is of little significance.
Simply explained
Like multiple alternative paths and spare parts, so that a service continues to run when a component fails.
Why it matters in practice
Relevant for business-critical websites, APIs, and automations where downtime has direct consequences.
Example from business
Possible example: A web application runs across multiple instances. A properly configured load balancer detects repeatedly failed health checks and routes requests to remaining healthy instances. If all targets are faulty, behavior may vary.
Limits and pitfalls
- Equating redundancy with high availability; overlooking common single points of failure; confusing backups with failover; not conducting recovery tests.
Origin & history
In cloud architectures, resilience measures are intended to maintain operation during failures or enable efficient recovery.
Use in mid-sized companies
- Possible applications: redundant web services, databases, queues, and integration platforms.
Frequently asked questions
Does HA mean a system never fails?
No. Is backup the same as HA? No, backup primarily serves recovery, HA ensures ongoing availability.
Sources
- Reliability · Google Cloud Architecture Framework, Reliability
- ALB Health Checks · AWS, ALB Health Checks
- Multi-AZ · AWS RDS, Multi-AZ
Source verification: 11.10.2026.
Editorially reviewed on: