To ensure seamless user experience during system failures at peak traffic, start by implementing autoscaling to automatically allocate resources based on demand, ensuring the system can handle spikes in traffic. Utilize load balancing to distribute traffic evenly across servers, preventing any single point of failure. Deploy caching mechanisms to reduce server load by serving static or frequently accessed data more quickly. Set up failover strategies with redundant systems that can take over if primary systems fail. Monitor the system in real time using alerting tools, and have a rapid response team ready to address issues. Continuously test for peak conditions to identify and fix vulnerabilities.

The type of failure will suggest which approach to take. Some issues can be resolved by throwing more hardware at them. Scale up the number of copies of that application. Some issues need more resources at some point. More memory, faster network. Another thing to look at is some demand exceeding quotas, like number of sessions.

- Thorough system stress testing to identify system bottleneck areas - Use analytics tools like splunk , grafana , promethus to find user traffic trends , technical component utilization during peaks hours - Understand if a specific functionality is causing requwst saturation or its overall application leading to request saturation - Having micro based service architecture helps in such cases to understand at which layer traffic delays or breaks. And having RCA to problem is key before going for scaling infra resources for long term fix

Maintain system capacity and redundancy in your pocket - and keep up to date system records, architectures and configs. Prepare, rehearse scenarios, keep first line maintenance trained and second line maintenance on call. Understand your systems: a crisis is a bad time to uncover a single point of failure or improvisational automation. Respond and communicate outward - keep your higher-ups in the loop, and use your business comms channels to work with customers if you need. Make sure your team is clear on who is external facing and managing the situation, vs internal facing and managing the system. Mostly people can't do both effectively at the same time.

To ensure seamless user experience during system failures at peak traffic One should always strive to preserve the following rules at the level of a company and especially of R&D 1. User communication - maintain a public status page to inform users of the system 2. Longevity and Load testing - regularly conduct load testing to understand system limits 3. Monitoring - implement robust monitoring solutions (e.g., Prometheus, Grafana) to track system performance 4. Optimization: Optimize resource usage through container orchestration tools(e.g., Kubernetes)

I assume system failure is reality and thinking scalable , high available , auto healed architecture isn’t purpose of this question but instead during such situations how to increase user satisfaction and confidence. I think user communication, updates and showing good message and acknowledging issue has to be there. afterwards as a first priority recovering situation and indicating with estimated resolution plan etc to gain user confidence and their plan to use system. After recover and root cause share clear root cause and if there are systems design issues, share plan to reduce similar incident in future and proactive monitoring to ensure robustness of system.

At first I will ensure that my query is enough optimized. Then I will must use caching where it can be used. Sometimes caching for 1/2 second in landing/Other pages create a impact on high traffic . After that will ensure asynchronous process where its needed .. like reporting , sending mail,sms etc.. Also I will ensure rate limiting as per requirements , Circuit breaker, load balance etc.. Although traffic is huge , then I will use db replication if read data is heavier.. But If the Write data is heavier than have to go for partioning, If much heavier than will go for sharding.. Finally there's lot of solutions & their props & cons.. We have to decide before using & implement those as per business requirements

Communication is critical during such an incident. Root cause analysis is essential for eliminating the incident from repeating. And, in general, proper planning and architecture that takes into account peak times vs. SLA to be made well in advance, and continuously. Have a communication, mitigation and contingency plans in place, and make sure to be practicing them periodically.