What are Active-Active and Active-Passive architectures?
And how to choose the right high-availability strategy
What is high availability in the context of web applications and why is it so important?
Imagine you build and release a web application for your users around the world.
Everything is going well and your users are happy with the services you provide.
But one day a server goes down in your European region and now all of your European users suddenly cannot use your website, causing them frustration and impacting your reputation.
High availability is the idea of your web application being available even when servers go down in different geographical locations.
With various strategies, you can failover user requests to your app in the impacted location to another location that is fully functional.
Instead of hitting a blank error page, your users will be able to use the application all the same, albeit a little slower since they are now being redirected to another server often a bit farther away.
By having multiple servers that host copies of your web app, you can serve different customers around the world and let them be redirected to other servers in case of failures.
To remain highly available there are two commonly used approaches in the cloud:
Active-active setup
Active-passive setup
Let’s explore the differences between these two strategies and discuss how to choose the right approach for your application.
Active-Active Architecture
An active-active architecture involves running multiple instances of an application simultaneously, with all instances actively serving traffic.
Each instance is usually deployed across different regions or availability zones (AZ) to distribute traffic requests and reduce the risk of single points of failure.
In an active-active architecture, requests are distributed among the instances using load balancers or DNS routing policies.
This allows for efficient utilization of resources and ensures low-latency access for users by directing traffic to the nearest available instance.
The most notable features of active-active architectures include:
High Scalability: Active-active architectures are highly scalable, as they can handle high traffic loads by distributing workloads across multiple instances.
Low Latency: active-active architectures minimize latency and provide optimal user experience since the data is closer to the end users.
High Availability: Since all instances are active and serving traffic simultaneously, there’s no downtime during failover or server maintenance.
Active-Passive Architecture:
In comparison, active-passive architecture involves running one active instance of the application while keeping another instance in standby mode.
The standby instance, also known as the passive instance, remains idle until it’s needed to serve traffic requests in the case when the active/primary instance fails or requires maintenance.
In an active-passive architecture, the standby node is usually located in a different region or AZ to ensure high availability.
In a managed platform like AWS, configurations are automatically set up to detect when a server instance has failed and to redirect all traffic requests to the standby instance.
The most notable features of active-passive architectures include:
Fault Tolerance: Active-passive architectures provide fault tolerance by maintaining a standby instance ready to take over in case of the primary server failure.
Cost Efficiency: Since the passive node remains idle most of the time, active-passive architectures can be more cost-effective than active-active architectures.
Disaster Recovery: Active-passive architectures are useful in disaster recovery scenarios, as they allow for quick failover and minimal downtime in the event of a failure due to physical disasters.
Choosing the Right Approach
When deciding between active-active and active-passive architectures for your application, there are various factors to consider.
In my experience, the most important ones to consider are:
Application’s traffic patterns
Cost-effectiveness
Backup & Disaster recovery protocols
Complexity and management
Active-active architectures are ideal for applications with consistently high traffic requests, while active-passive configurations are more suitable for unknown or inconsistent traffic.
In terms of costs, you should consider the cost implications of both architectures and apply the ones that have the best trade-offs for your business goals. Remember that active-active architectures incur higher costs due to having multiple active servers.
Assess the importance of disaster recovery capabilities for your app. If disaster management is an important element of your app, you may want to consider an active-passive architecture to rapidly failover in case of regional server failures.
Lastly, you should also consider the complexities of managing each architecture. An active-active architecture requires sophisticated load balancing and traffic routing, while an active-passive architecture involves less complex management and configuration.
Conclusion
In conclusion, both active-active and active-passive architectures offer their own advantages for achieving high availability and fault tolerance in the cloud.
The choice between the two depends on factors such as traffic patterns, cost considerations, geographic redundancy requirements, and management complexity.
By carefully evaluating these factors and understanding the trade-offs, you can select the right approach to ensure the reliability and resilience of your application in the cloud.
👋 My name is Uriel Bitton and I hope you learned something of value in this article of The Serverless Spotlight.
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Uriel