Using an auto scaling service for elastic compute is the best fit for the scenario described, where consistent compute power is required with the flexibility to scale up during traffic surges. This service will automatically adjust the number of compute instances to handle the load, providing a balance between performance and cost. A serverless function execution platform, while ideal for certain event-driven patterns, does not provide a persistent baseline environment which web applications typically require. Using a larger fixed compute instance may lead to cost inefficiencies due to over-provisioning during non-peak times. Data processing managed services are not suitable as they are tailored for batch jobs and not interactive platforms with variable traffic.