Active Active and Active Passive Database

Active-Active

An active-active cluster is typically made up of at least two nodes, both actively running the same kind of service simultaneously. The main purpose of an active-active cluster is to achieve load balancing. Load balancing distributes workloads across all nodes in order to prevent any single node from getting overloaded. Because there are more nodes available to serve, there will also be a marked improvement in throughput and response times.

Active-Passive

Like the active-active cluster configuration, an active-passive cluster also consists of at least two nodes. However, as the name “active-passive” implies, not all nodes are going to be active. In the case of two nodes, for example, if the first node is already active, the second node must be passive or on standby.

Database Topologies

There are pros and cons to each type of database deployment, Multi Active or Active Passive. There are a couple of things to consider when designing a resilient database architecture. and in this blog we will outline these.

Single Site

Single Node
  • Cost Effective as only one node is licensed. However the cost of an outage to the business if running this model in production could be astronomical in terms of lost revenue and productivity.
  • Lack of HA. If the node goes down or has issues there is no failover. You have to fix the existing node or restore from a backup
  • Any maintenance that could cause downtime has to be factored in around slow traffic times but there will always be some form of customer/service impact when completing patching or upgrades etc.
Active-Passive
  • Still relatively cost effective as some providers allow you to run a passive node for no charge providing you have an active support contract
  • Provides a lot better HA capability than single node architecture
  • Can get expensive if you have to license the secondary node(s) as you are paying for hardware resources that are not used. The only time they are used is in the event of a disaster or failure.
  • Expensive in terms of operational cost as in the event of a failure all the servers need to be re-synced in order to get back to an active passive configuration.

Multi-Active Model

Multi Active Single Site
  • Scalability of both Read and Write operations
  • Always on availability meaning no downtime when completing maintenance tasks like upgrades and patching.
  • Cost effective in terms of resource utilisation as all nodes are actively used all of the time. This makes these solution to be some of the most cost effective solutions on the market although a higher up front licensing cost may be observed.
  • RPO of 0 and RTO < 10 seconds
  • Most of these solutions will have a performance hit due to some network traffic involved. Although one database in particular is better than other in this case. This is usually minimal in the single site model due to the network being super quick with lots of bandwidth.
  • Some of the technologies like Cassandra need regular maintenance jobs ie recovery operations to be completed to ensure the data on all nodes is replicated and consistent.
Multi Site Multi Active

Conclusion

As you can see from the pros and cons of each solution, I hope this will help you decide on the correct deployment for you applications. Whichever solution you pick needs to meet your requirements in terms Business Continuity(HA and DR),Cost (Not only in terms of $ but also in terms of operational and outage cost. A full TCO model should be considered) and performance needs.

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