The secure container that hosts a single container in a micro virtual machine (VM) is now used in serverless computing, as the containers are isolated through the microVMs. There are high demands on the high-density container deployment and high-concurrency container startup to improve both the resource utilization and user experience, as user functions are fine-grained in serverless platforms. Our investigation shows that the entire software stacks, containing the cgroups in the host operating system, the guest operating system, and the containerrootfsfor the function workload, together result in low deployment density and slow startup performance at high-concurrency.We propose a lightweight and holistic-scalable secure container runtime, named RunD-V, to resolve above problems in serverless computing. RunD-V proposes a guest-to-host runtime template for microVM scaling-out, and CR-bind feature in guest kernel for microVM scaling-up. Using guest-to-host runtime template, over 200 secure containers can be launched within 1son a node equipped with 104 vCPUs. It also enables more than 2,500 secure containers to be deployed on a node with 384GB of memory. The vertical scaling mechanism CR-bind further enhances both startup concurrency and deployment density.