Resilient Architecture Concepts

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• One benefit of cloud is the potential to provide services resilient to failures at different levels
  • e.g., components, servers, local networks, sites, datacenters, and wide area networks
• CSP uses a virtualization layer to ensure that computer, storage, and network provisions meet the availability criteria set out in its SLA

High Availability

High availability (HA) is a metric that defines how closely systems approach the goal of providing data availability 100% of the time while maintaining a high level of system performance.

• CSP uses redundancy to make multiple disk controllers and storage devices available to a pool of storage resources
  • data may be replicated between pools or groups
  • each pool supported by separate hardware resources

Replication

Replication is automatically copying data between two processing systems either simultaneously on both systems (synchronous) or from a primary to a secondary location (asynchronous).

• allows businesses to copy data to where it can be utilized most effectively
• cloud may be used as a central storage area
  • makes data available among all business units
• requires:
  • low latency network connections
  • security
  • data integrity
• several data storage performance tiers
  • e.g., hot storage and cold storage
  • the quicker the data retrieval, the higher the cost
• Different applications have diverse replication requirements
  • e.g., database needs low-latency, synchronous replication
    • transaction cannot be considered complete until it has been made on all replicas

High Availability Across Zones

• CSPs divide the world into regions
• Each region is independent
• regions are divided into availability zones
  • have independent datacenters with their own power, cooling, and network connectivity
• Provisioning resources in multiple zones and regions can:
  • improve performance
  • increase redundancy
  • but it requires an adequate level of replication performance
• several tiers of replication representing different high availability service levels:
  • Local replication
    • replicates your data within a single datacenter in the region where you created your storage account
    • replicas are often in separate fault domains and upgrade domains
  • Regional replication
    • aka zone-redundant storage
    • replicates your data across multiple datacenters within one or two regions
    • safeguards data and access in the event a single datacenter is destroyed or goes offline
  • Geo-redundant storage (GRS)
    • replicates your data to a secondary region that is distant from the primary region
    • safeguards data in the event of a regional outage or a disaster