What Is High Availability?
High availability (HA) is the ability of a system to keep working when parts of it fail. It's built by removing single points of failure: running more than one copy of each critical component, checking their health continuously, and switching traffic away from anything that breaks, automatically and quickly.
Availability is usually measured as a percentage of uptime over a month or year, often described in "nines".
What the Nines Mean
Availability | Downtime per month | Downtime per year |
99% | About 7.3 hours | About 3.65 days |
99.9% | About 43.8 minutes | About 8.8 hours |
99.95% | About 21.9 minutes | About 4.4 hours |
99.99% | About 4.4 minutes | About 53 minutes |
Each extra nine costs more to build and run. The right target depends on what an hour of downtime costs your business.
This Is For You If...
Your app runs on a single server or database
Deploys or maintenance cause downtime
Customers or contracts require an uptime SLA
A past outage cost you revenue or a customer
You serve schools, hospitals or businesses that depend on you during working hours
What We Build
Redundant Application Servers
Several app instances behind a load balancer, spread across availability zones. See Load Balancer Setup.
Stateless Services
Sessions, uploads and jobs moved out of individual servers, so any instance can handle any request.
Highly Available Databases
Replicas with automatic failover, such as Amazon RDS Multi-AZ, Cloud SQL HA or Patroni for PostgreSQL. See Replication & Backup.
Health Checks and Self-Healing
Automatic removal and replacement of failed instances, including on Kubernetes.
Zero-Downtime Deploys
Rolling or blue-green deploys with automatic rollback. See Deployment.
Edge Protection
CDN, caching and DDoS protection, so traffic spikes and attacks don't take you down. See WAF & DDoS Protection.
Common Single Points of Failure
Single point | What happens when it fails | Fix |
One app server | The whole app goes down | Two or more servers behind a load balancer |
One database | All reads and writes stop | Replica with automatic failover |
One availability zone | A data center issue takes you offline | Spread across zones |
Manual deploys | Every release risks downtime | Automated rolling deploys |
One person who knows the system | Nobody can fix it at night | Runbooks and on-call rotation |
Common Mistakes to Avoid
Instinct | Why It Doesn't Help | Do This Instead |
Buying a bigger server | It's still a single point of failure | Run several smaller instances |
Adding replicas without testing failover | Failover often fails when first needed | Test failover regularly |
Aiming for 99.99% everywhere | Costs rise steeply for each nine | Set targets per service based on business impact |
Ignoring dependencies | A third-party outage still takes you down | Add timeouts, retries and fallbacks |
How It Works
1. Assess
Map components, dependencies and single points of failure
2. Set targets
Agree availability targets per service
3. Design
Plan redundancy, failover and deploy changes
4. Build
Implement and automate the changes
5. Test
Simulate failures and confirm the system stays up
6. Monitor
Alerts and dashboards for availability. See Monitoring & Observability
Why Codersarts
We build and run production systems, so high availability is designed around how your app actually works, and tested by breaking things on purpose before real failures do.
Turnaround Time
An availability assessment takes 3 to 5 working days. Building redundancy for a typical web app usually takes 1 to 4 weeks.
FAQ
What is the difference between high availability and disaster recovery?
High availability keeps the system running through small failures, like a server or zone going down. Disaster recovery restores service after a major event. See Disaster Recovery.
How much uptime do I need?
Most business apps target 99.9% to 99.95%. Higher targets make sense when downtime directly costs significant revenue or safety.
Does high availability require Kubernetes?
No. Load balancers, multiple servers and managed databases achieve it for most apps. Kubernetes helps at larger scale.
Can you make our app highly available on Hetzner?
Yes, using Hetzner load balancers, several servers and replicated databases. See Hetzner Server Setup.
Is our project kept confidential?
Yes. Your data, code, and systems stay confidential, and an NDA is available on request.
Fixed-Price Tasks to Start With
Load Balancer Setup: spread traffic across servers
Uptime Monitoring & Alerts Setup: know the moment something fails
Load Test Your App: find your limits before users do
Related Services
Could One Failure Take You Offline?
Find your single points of failure and remove them.