An internet television service migrated from a system supporting 5k users to one supporting 5 million users using Apache Cassandra in a microservices architecture. Key lessons learned included putting state on clients or in Cassandra, not other systems; testing different data models and workloads; following DataStax documentation; avoiding Thrift; ensuring proper DevOps practices; and running multi-node Cassandra clusters. A live migration from MySQL to Cassandra involved double writing to make writes idempotent. Cassandra allows greater scale than other databases by requiring data denormalization and duplication.