Availability is defined as the proportion of time a system is up and serving the traffic. It is defined in terms of percentage. Can also be divided into tiers of 2 nines (99%), 3 nines (99.9%), 4 nines (99.99%), 5 nines (99.999%) and 6 nines (99.9999 %).
Ways to improve Availability
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Redundancy : It is a way of having backup components which can takeover when primary components fail.
Technique to Add Redundancy
- Server Redundancy: Having multiple instance of the same server helps in distributing traffic across servers, ensuring if one fails other can provide service.
- Database Redundancy: Creating a replica database that can takeover when primary database fails.
- Geographic Redundancy: Distributing resources across multiple geographic locations to solve/mitigate the regional failures
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Load Balancing: It distributes the incoming traffic across multiple servers to ensure that no single server becomes a bottleneck this improving performance and availability.
Technique to Add Load Balancing
- Hardware Load Balancing: Physical devices that distributes traffic based on preconfigured rules.
- Software Load Balancing: Software solutions that manage traffic distribution. Solutions like HAProxy, Nginx, or cloud-based solution like AWS Elastic Load Balancer.
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Data Replication: It is a way of copying data to multiple locations either asynchronously or in realtime ensuring data is available even one location fails.
Technique of Data Replication
- Synchronous Replication: Data is replicated in real-time to ensure consistency across location.
- Asynchronous Replication: Date is replicated with delay, which can be more efficient but may result in slight data inconsistencies.
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Failover Mechanism: Failover mechanism automatically witches to redundant system when a failure detected.
Techniques of Failover Mechanism
- Active-Passive failover mechanism: A primary active component is backed by a passive standby component that takes over upon failure.
- Active-Active failover mechanism: All components are active and share the load. If one fails, remaining components continue to handle the load seamlessly.
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Monitoring & Alerts: Continuous health monitoring involves checking the status of the system components to detect failures early and trigger alert for immediate action.
Techniques for Monitoring & Alerts
- Heartbeat Signals: Regular signals sent between components to check their status.
- Health Check: Automated scripts or tools that perform regular check on components.
- Alerting systems: Tools like PagerDuty or OpsGenie that notify administrators of any issues.
Best practices for Availability
- Build for failure: Assume that components can go down at any moment and build the required fall back mechanisms
- Implement Health Check
- Use Multiple availability zones: Distribute the system across multiple data centers to prevent localized failures.
- Practice chaos Engineering: Check reliability by intentionally introducing failures.
- Implement Circuit Breakers: Prevent cascading failures by quickly cutting off problematic services
- Use caching wisely: Caching can reduce load on databases.
- Plan for capacity: Ensure your system can handle both expected and unexpected loads.
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