OpenStack Architecture
OpenStack follows a modular, service-oriented architecture where each component provides a specific function through well-defined APIs. Services communicate via message queues and RESTful APIs, creating a loosely coupled system that can scale horizontally.
Logical Architecture
OpenStack Core Services Architecture
Physical Architecture
Typical Multi-Node Deployment
Conceptual Layers
1. User Interface Layer
End users and administrators interact with OpenStack through multiple interfaces:
- Horizon Dashboard: Web-based GUI for managing resources
- CLI Tools: Command-line clients for each service (nova, neutron, etc.)
- Direct API: RESTful APIs for automation and integration
- Third-party Tools: Terraform, Ansible, SDKs in various languages
2. Control Plane
The control plane consists of API services, schedulers, and management components:
- API Services: Receive and process user requests
- Schedulers: Decide where to place VMs and resources (nova-scheduler, cinder-scheduler)
- Database: Stores state and configuration (typically MySQL or MariaDB)
- Message Queue: Coordinates asynchronous communication (RabbitMQ or similar)
- Keystone: Centralized authentication and service catalog
3. Data Plane
The data plane consists of compute, storage, and network resources:
- Compute Nodes: Run hypervisors and host VM instances
- Storage Systems: Provide block, object, and file storage
- Network Infrastructure: Physical and virtual networking (switches, routers, SDN)
Communication Flows
Example: Launching a VM Instance
- User authenticates with Keystone and receives a token
- User sends VM launch request to Nova API with the token
- Nova API validates token with Keystone
- Nova Scheduler selects appropriate compute node based on resources and policies
- Nova Conductor retrieves image metadata from Glance
- Neutron allocates network resources (IP address, ports)
- Cinder attaches any required block volumes
- Nova Compute on selected node downloads image from Glance
- Hypervisor launches the VM instance
- Status updates propagate back through the message queue
Network Architecture
OpenStack networking typically involves multiple network types:
| Network Type | Purpose | Typical VLAN/Subnet |
|---|---|---|
| Management Network | Internal communication between OpenStack services | 192.168.1.0/24 |
| Tenant Network | VM-to-VM communication within projects | 10.0.0.0/8 (VXLAN/GRE) |
| External Network | Public internet access, floating IPs | Public IP ranges |
| Storage Network | Block and object storage traffic | 172.16.0.0/24 |
| API Network | API endpoint access for users | Often same as Management |
High Availability Architecture
Production OpenStack deployments implement HA at multiple layers:
- Load Balancers: HAProxy or hardware load balancers distribute API requests across controllers
- Database Clustering: MySQL/MariaDB with Galera for multi-master replication
- Message Queue Clustering: RabbitMQ in mirrored queue configuration
- Shared Storage: NFS or clustered file systems for shared state
- Pacemaker/Corosync: Cluster resource management for service failover
- Network Redundancy: Bonded interfaces, redundant switches, multiple paths
Best Practices
- Deploy minimum 3 controller nodes for quorum-based HA
- Use separate physical networks for management, storage, and tenant traffic
- Implement redundant network paths and bond network interfaces
- Plan for horizontal scaling of compute nodes from day one
- Use configuration management (Ansible, Puppet) for consistent deployments
- Monitor all layers with tools like Prometheus, Grafana, and Nagios
Understanding OpenStack's architecture is crucial for successful deployment and operation. The modular design allows you to start simple and expand as needed, while the distributed architecture enables massive scale.