Runa is a SaaS startup that uses machine learning and big data techniques to dynamically insert personalized promotions on e-commerce merchants' websites in real-time. They capture activity data from every merchant page view and store it indefinitely as the number of merchants grows. Their tech challenges include handling the step function increase in data from adding merchants, batch processing for analytics, and real-time rule-based promotions. They initially prototyped on AWS for its flexibility and low costs, and have since incrementally added more scalable technologies like Hadoop, HBase, and Chef on AWS to handle their growing infrastructure needs.