Active Passive & Active Active Architecture for High Availability System

Active-Passive and Active-Active architectures stand out as two important strategies for achieving high availability. These architectures offer distinct approaches to distributing workloads, managing resources, and mitigating downtime, each tailored to address specific operational requirements and scalability demands.

What is Active-Passive Architecture?

Active-passive architecture, also known as standby or failover architecture, is a high availability configuration in which numerous identical systems are deployed, but only one is actively serving production traffic at a given time. The passive system(s) remain inactive until needed, acting as backups in case the active system fails. The major purpose of active-passive architecture is to assure service continuity by swiftly switching to the standby system if the active system fails.

Components and Characteristics of Active-Passive Architecture

Active-passive architecture features two sets of components: active and passive. The active components handle normal operations, while the passive ones remain on standby, ready to take over in case of failure.

• Primary (Active) Server: Under typical operational conditions, this server is the primary (active) server for production traffic. It is the primary point of contact for users of the service or application.
• Standby (Passive) Server(s): These servers are in standby mode, or effectively on standby, until they are required to take over operations from the primary server. They duplicate the primary server’s configuration and data to provide a smooth transition in the event of failure.
• Heartbeat Mechanism: A heartbeat mechanism is used to constantly check the health and availability of an active server. This mechanism detects symptoms of failure, such as unresponsiveness or system problems.
• Data Replication: Data replication procedures keep the data on the standby server(s) in sync with the data on the active server. This synchronization reduces the likelihood of data loss during failover and guarantees that the standby system can easily take over operations.

Failover Process and Recovery Mechanisms in Active-Passive Architecture

• Failure Detection: The heartbeat system detects when the active server fails or becomes unavailable. This might be a result of device failure, software flaws, or network problems.
• Automatic Failover Trigger: When a failure is detected, the failover procedure is initiated automatically. This procedure comprises starting the backup server to take over the functions of the failing primary server.
• Traffic Redirection: Traffic is diverted from the failing primary server to the backup server to ensure that users continue to receive service.
• Standby Server Activation: The standby server takes over as the new active server, taking all of the tasks formerly held by the primary server.
• Recovery methods: After activating the standby server, recovery methods guarantee that data stays consistent and the service or application resumes to normal operation without any noticeable impact on users.

Use Cases of Active-Passive Architecture

Active-Passive architecture is ideal for ensuring fault tolerance, disaster recovery, and continuous service availability.

• Disaster Recovery Systems: Active-Passive architecture is commonly used in disaster recovery setups where one set of components remains passive until a failure occurs. For instance, in database systems, a passive replica is kept synchronized with the active database. If the active database fails, the passive replica takes over to ensure data availability.
• E-commerce Websites: Many e-commerce websites implement Active-Passive architecture to ensure high availability and fault tolerance. While the primary server handles user requests, a passive backup server remains on standby. If the primary server experiences issues, the backup server is activated to maintain continuous service.
• Banking Systems: Banks often employ Active-Passive architecture for critical systems such as online banking platforms and ATM networks. In the event of a server failure or network outage, redundant servers or backup systems are activated to prevent service disruptions and ensure customers can continue to access their accounts.

Benefits of Active-Passive Architecture

Below are some benefits of Active-Passive Architecture:

• Simplicity: Active-passive designs are easier to set up and administer than more complicated ones.
• Cost-Effectiveness: They can be cost-effective for applications with low to moderate traffic levels since they use fewer resources than active-active designs.
• Failover Reliability: Failover techniques ensure dependable service continuity, resulting in little downtime in the event of a failure.

Challenges of Active-Passive Architecture

Below are some challenges of Active-Passive Architecture:

• Resource Underutilization: During normal operation, the standby server(s) are idle, resulting in resource underutilization and possible inefficiencies.
• Longer Recovery Times: Compared to active-active designs, recovery times in active-passive configurations may be longer since the backup server must be enabled and brought online before it can take over production activities.

What is Active-Active Architecture?

Active-active architecture is a high availability configuration in which numerous identical systems serve production traffic concurrently. In contrast to active-passive design, in which one system is active while others sit idle until needed, active-active architecture involves all systems actively processing user requests. This configuration offers enhanced scalability, fault tolerance, and performance.

Components and Characteristics of Active-Active Architecture

Active-active architecture involves multiple sets of components, all actively processing requests concurrently.

• Multiple Active Servers: In an active-active architecture, numerous servers are installed, each of which actively handles production traffic. Each server functions autonomously and is capable of serving user requests.
• Load Balancer: A load balancer lies in front of active servers, distributing incoming requests among them. It guarantees that traffic is distributed evenly, maximizes resource use, and improves response times.
• Data Synchronization: Data synchronization techniques make sure that data is consistent across all active servers. This guarantees that consumers get consistent and up-to-date information regardless of which server processes their request.
• Health Monitoring: Continuous server health monitoring discovers problems or malfunctions early on. If a server fails or its performance deteriorates, the load balancer can transfer traffic to other healthy servers.

Load Balancing and Traffic Distribution Strategies in Active-Active Architecture

• Round-robin: Requests are delivered in a circular pattern across active servers to ensure an equitable distribution of traffic.
• Least Connections: Requests are directed to the server with the fewest active connections, which helps to equally share the demand.
• Weighted Round-robin: Different weights can be allocated to servers based on their ability to handle traffic, resulting in more effective resource use.

Real-World Examples and Use Cases of Active-Active Architecture

Active-Active architecture is suitable for scenarios requiring high scalability, performance, and real-time processing.

• Content Delivery Networks (CDNs): CDNs distribute website content across multiple servers located in different geographical regions. With Active-Active architecture, CDNs can serve user requests from the nearest server, ensuring faster content delivery and reducing latency. Examples include Cloudflare and Akamai.
• Online Marketplaces: Platforms like eBay and Amazon utilize Active-Active architecture to handle high volumes of transactions. Multiple data centers or availability zones are active simultaneously, processing user requests concurrently. This ensures uninterrupted service even during peak traffic periods.
• Social Media Platforms: Social media networks such as Facebook and Twitter employ Active-Active architecture to manage millions of user interactions in real-time. By distributing the workload across multiple active components, these platforms maintain responsiveness and reliability, even during surges in user activity.

Benefits of Active-Active Architecture

Below are some benefits of Active-Active Architecture:

• Improved Scalability: Active-active design enables horizontal scalability by adding more servers to the pool to handle growing traffic and strain.
• Higher Resource use: All servers actively manage traffic, optimizing resource use while minimizing waste.
• Greater Performance: Active-active architectures can provide users with greater performance and response times by equally distributing traffic through load balancing.

Challenges of Active-Active Architecture

Below are some challenges of Active-Active Architecture:

• Complexity: Active-active topologies are more difficult to establish and operate than active-passive configurations. To achieve a flawless functioning, proper configuration and coordination are essential.
• Cost Increases: Deploying and maintaining numerous active servers, coupled with a load balancer, can raise infrastructure expenses as compared to active-passive arrangements.

Factors Influencing Architecture Selection

Choosing between Active-Active and Active-Passive architectures depends on how much you want all components to work together at once.

• Application Requirements: The application’s unique requirements, such as availability, scalability, and performance, play an important influence in establishing the suitable architecture. For example, applications that require high availability may benefit from active-active designs, whilst those with lower demands may choose active-passive configurations.
• Budget Constraints: The financial resources available for infrastructure installation and upkeep impact architectural choice. More complicated designs often need more investments in hardware, software, and maintenance.
• Complexity Tolerance: The degree of complexity that an organization or team can effectively manage is an important consideration. While active-active systems improve scalability and performance, they are more difficult to establish and manage than active-passive configurations.
• Existing Infrastructure and Technologies: The compatibility and integration with existing infrastructure and technologies have an influence on design decision. Organizations may adopt designs that are compatible with their existing systems in order to reduce disruption and enable integration.
• Regulatory and Compliance Requirements: Regulatory and compliance standards may impose specific architectural requirements, especially in areas such as banking, healthcare, and government. Compliance with rules like GDPR, HIPAA, and PCI DSS may have an impact on architectural decisions.
• Expected Traffic Patterns: Expected traffic patterns, such as peak loads and changes in user demand, influence architectural decisions. Architectures must be able to scale dynamically to handle fluctuating levels of traffic while maintaining performance and reliability.