OpenStack multi-datacenter deployment strategies: choosing the right architecture

When designing OpenStack installations for enterprise environments, reliability and resilience are paramount concerns. Organizations need to ensure their cloud infrastructure can withstand datacenter failures while maintaining service availability and data integrity.

There are three main architectural approaches for deploying OpenStack across multiple locations, each with distinct advantages and trade-offs:

• Single region / single location - Traditional centralized deployment
• Multi-region installation - Independent clusters with shared identity
• Single region stretched across multiple datacenters - Unified cluster spanning locations

This post provides a comprehensive overview of these deployment patterns to help you choose the right architecture for your requirements.

1. Single region installation in single location

This is the most common and straightforward OpenStack deployment pattern. The entire OpenStack cluster operates within a single physical location, providing excellent performance and simplified management.

Architecture components

Control plane redundancy:

• Distributed across 3+ servers for high availability
• HAProxy provides single API entry point for public and internal endpoints
• Database replication (MySQL/MariaDB with Galera cluster)
• AMQP message queue replication (RabbitMQ cluster)
• Supporting services like Memcached and Redis are also clustered

Compute resources:

• Compute nodes can be organized into multiple Availability Zones
• AZs may represent different rooms, racks, or blade chassis
• Provides protection against localized hardware failures

Storage architecture:

• Relies on internal redundancy mechanisms
• Storage array replication or Ceph distributed storage

Single region OpenStack deployment with control plane, compute nodes, and storage in one location

Pros and cons

✓ Advantages

• •
  Simplified management: Single control plane and network
• •
  Optimal performance: Low latency between components
• •
  Cost-effective: Minimal infrastructure requirements
• •
  Easy troubleshooting: Centralized logging and monitoring

⚠ Limitations

• •
  Single point of failure: Entire datacenter outage affects all services
• •
  Limited disaster recovery: No geographic separation
• •
  Scalability constraints: Bound by single location capacity

2. Multi-region deployment

Multi-region deployment provides geographic distribution and disaster recovery capabilities by deploying independent OpenStack clusters across multiple locations while sharing common identity services.

Architecture overview

Regional independence:

• Each region operates as a separate OpenStack cluster
• Local storage and compute resources within each region
• Independent control plane services (Nova, Neutron, Cinder, etc.)

Shared identity layer:

• Keystone - Centralized authentication across all regions
• Horizon - Single web interface for multi-region management
• Service Catalog - Region-specific API endpoints after authentication

Quorum and split-brain protection:

• Third location serves as tie-breaker/witness
• Keystone, Horizon, and backend services replicated to witness location
• Database, Memcached clusters span three locations for quorum

Multi-region deployment with independent clusters and shared identity services

Pros and cons

✓ Advantages

• •
  Geographic redundancy: Protection against regional disasters
• •
  Independent clusters: Regional failures don't affect other regions
• •
  Unified identity: Single authentication across all regions
• •
  Scalability: Can add new regions independently

⚠ Limitations

• •
  No cross-region migration: VMs and data bound to specific regions
• •
  Complex management: Multiple control planes to maintain
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  Network overhead: Inter-region communication latency
• •
  External tooling required: For cross-region data replication

3. Single region stretched across multiple datacenters

The stretched cluster approach provides the best of both worlds: single cluster management with multi-datacenter resilience. This architecture enables live migration and immediate failover while maintaining geographic distribution.

Architecture components

Unified control plane:

• Control plane services distributed across 3 datacenters
• Single OpenStack cluster with unified API endpoints
• Enables seamless VM migration between locations

Stretched storage solutions:

• Metro-cluster storage with synchronous replication
• Ceph stretched cluster across multiple sites
• Storage accessible from all datacenters
• Tie-breaker location prevents split-brain scenarios

Availability zone segregation:

• Each datacenter represents a separate Availability Zone
• Users can specify VM placement by datacenter
• Automatic workload distribution and evacuation capabilities

Stretched cluster spanning multiple datacenters with unified control plane

Pros and cons

✓ Advantages

• •
  Live migration: VMs can move between datacenters seamlessly
• •
  Single management interface: Unified control plane
• •
  Immediate failover: Automatic workload evacuation
• •
  Geographic redundancy: Protection against datacenter failures
• •
  Flexible placement: Users can control VM location via AZs

⚠ Limitations

• •
  Network latency sensitive: Requires low-latency interconnects
• •
  Complex storage: Metro-cluster or stretched Ceph required
• •
  Higher cost: Synchronous replication and redundant infrastructure
• •
  Distance constraints: Limited by storage replication capabilities

Architecture decision framework

Selecting the optimal deployment strategy requires careful evaluation of your organization’s technical constraints, business requirements, and operational capabilities. Here’s a practical decision framework:

Technical constraints assessment

Network infrastructure:

• Single region: Standard datacenter networking sufficient
• Multi-region: Reliable WAN links between sites
• Stretched cluster: Dedicated low-latency links (<10ms RTT, 10Gbps+ bandwidth)

Distance limitations:

• Single region: No distance constraints
• Multi-region: No distance limitations between regions
• Stretched cluster: Maximum 100km between sites for synchronous storage replication

Storage requirements:

• Single region: Local storage arrays or Ceph cluster within datacenter
• Multi-region: Independent storage per region + external replication tools
• Stretched cluster: Metro-cluster storage or Ceph stretched mode (3+ sites)

Operational complexity comparison

Management overhead:

• Single region: One control plane, unified monitoring, single point of administration
• Multi-region: Multiple control planes, federated monitoring, complex troubleshooting across regions
• Stretched cluster: Single control plane but complex failure scenarios and network dependencies

Skill requirements:

• Single region: Standard OpenStack administration skills
• Multi-region: Multi-site coordination, cross-region networking knowledge
• Stretched cluster: Advanced storage networking, metro-cluster expertise, split-brain recovery procedures

Maintenance windows:

• Single region: Requires full service downtime for major updates
• Multi-region: Rolling maintenance possible with proper load balancing
• Stretched cluster: Zero-downtime maintenance with live migration capabilities

Recommendations

Choose single region when:

• Cost optimization is primary concern
• Acceptable downtime during datacenter maintenance
• Simple management is preferred
• Workloads don’t require geographic distribution

Choose multi-region when:

• Geographic compliance requirements exist
• Independent regional operations needed
• Cross-region migration is not required
• Willing to manage multiple control planes

Choose stretched cluster when:

• Live migration between sites is essential
• Single management interface preferred
• Budget allows for premium storage solutions
• Low-latency network connectivity available

Conclusion

Each OpenStack deployment pattern serves different business requirements and technical constraints. Single region deployments offer simplicity and cost-effectiveness, multi-region architectures provide maximum geographic redundancy, while stretched clusters deliver the ultimate in flexibility and seamless failover capabilities.

The key is understanding your organization’s priorities around cost, complexity, and availability requirements to make the optimal architectural choice.

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Categories: openstack architecture

Tags: infrastructure deployment architecture multi-datacenter reliability high-availability