With the promise of low-cost access to flexible and elastic compute resources, enterprises are increasingly migrating their existing workloads to cloud environments. However, the heterogeneity and complexity of legacy IT infrastructure make it challenging to streamline processes of migration at an enterprise scale. In this paper, we present Cloud Migration Orchestrator (CMO), a framework for automation and coordination of large-scale cloud migration based on the IBM Business Process Management (BPM) technology with pre-migration analytics. CMO seamlessly automates complex and error-prone tasks, spanning from on-premise data center analysis, using correlations between occurrences of middleware components, to parallel migration execution by integrating various vendor migration tools. CMO offers self-service capability with a 'one-click' migration execution and provides a solution for retaining IP addresses to further minimize workload remediation efforts. We present a taxonomy of network challenges, based on experience with migration of legacy environments and discuss how to automate and optimize network configurations. For each step of the migration process, starting from pre-migration assessment through the post-migration configuration, we discuss lessons learned from real-world deployments and demonstrate how the novel CMO framework reduces human activities through automation. Finally, we discuss efficiency of migration capabilities, including a fourfold process improvement (with respect to traditional approaches) using automation and orchestration.