Page Comparison

Levels of Redundancies

• Level 0: no redundancy
• Level 1: support manual failure detection & rerouting or recovery within a single site; expectations to complete in 30 minutes
• Level 2: support automated failure detection & rerouting 
  • within a single geographic site
  • stateless components: establish baseline measure of failed requests for a component failure within a site 
  • stateful components: establish baseline of data loss for a component failure within a site
• Level 3: support automated failover detection & rerouting 
  • across multiple sites 
  • stateless components 
    • improve on # of failed requests for component failure within a site 
    • establish baseline for failed requests for site failure 
  • stateful components 
    • improve on data loss metrics for component failure within a site 
    • establish baseline for data loss for site failure

Level 3 redundancy → Geo-Redundancy

Geo-redundancy types

active / standby 

cold standby

After health check failure detection, the administrator manually powers on the standby components and configures the all affected components. Stateful componentes are initialted with the latest backup.

warm standby

Resources of the standby components are allocated and will be periodically powered on for synchronization of the stateful components. After health check failure detection, the administrator manually configures the all affected components. 

hot standby

Resources of the standby components are allocated and powered on for periodic synchronization of the stateful components. After automatic health check failure detection, algorithms automatically configure the all affected components

active / active

High-availability clusters synchronize data of the cluster nodes almost in real-time. If one node fails the cluster remains full functional.