If you have subscribed to an Oracle Cloud Infrastructure (OCI) region that contains only one availability domain (AD), you can still achieve high availability for your application by leveraging fault domains within that single AD.
How to place components for high availability in a single availability
domain:
- Use Fault Domains: Each availability domain contains three fault domains, which are isolated groups of hardware within the AD. Fault domains provide anti-affinity, meaning that instances placed in different fault domains are physically separated on different hardware to avoid a single point of failure.
- Distribute Servers and Database Nodes Across Fault Domains:
- Place one web server in one fault domain and the second web server in a different fault domain.
- Similarly, place one database node in one fault domain and the second database node in another fault domain.
This distribution ensures that a hardware failure affecting one fault domain will not impact both servers or both database nodes simultaneously
- Use Load Balancer: Deploy a load balancer in front of the two web servers to distribute traffic and provide failover capability if one server becomes unavailable.
- Database High Availability: For the database tier, use a 2-node Oracle Real Application Clusters (RAC) system or equivalent to provide redundancy and failover capability within the single AD
Summary
Component| Placement Strategy| Purpose
---|---|---
Web Servers| One in Fault Domain 1, one in Fault Domain 2| Avoid single
hardware failure
Database Nodes| One in Fault Domain 1, one in Fault Domain 2| Ensure database
redundancy
Load Balancer| In front of web servers| Distribute traffic and failover
This approach leverages fault domains within the single availability domain to maintain high availability despite the limitation of having only one AD in the region
