In this paper, we present LinkLab 2.0, a completely pro- grammable and controllable IoT testbed with the support of edge devices and cloud infrastructures. To be more spe- cific, LinkLab 2.0 leverages a tiered architecture for the pro- grammable devices and the management system to achieve scalability. To better support the integrated experiment among IoT, edge and cloud, LinkLab 2.0 provides one-site pro- gramming support and leverages the customizable offloading with serverless functions. Moreover, LinkLab 2.0 proposes a device-involved multi-tenancy approach to ensure respon- siveness for concurrent requests. Furthermore, targeting 24/7 availability for experimenters, LinkLab 2.0 leverages proac- tive and reactive anomaly detection to improve the reliability of the testbed. Finally, we describe the supported research experiments and the outreach usage by external users. We also report lessons learned from the four-year operation. Lin- kLab 2.0 has supported experiments for 2,100+ users. The accumulated usage time across all the devices exceeds 17,300 hours.