Help Rather Than Recycle: Alleviating Cold Startup in Serverless Computing Through Inter-Function Container Sharing

In serverless computing, each function invocation is executed in a container (or a Virtual Machine), and container cold startup results in long response latency. We observe that some functions suffer from cold container startup, while the warm containers of other functions are idle. Based on the observation, other than booting a new container for a function from scratch, we propose to alleviate the cold startup by re-purposing a warm but idle container from another function. We implement a container management scheme, named Pagurus, to achieve the purpose. Pagurus comprises an intra-function manager for replacing an idle warm container to be a container that other functions can use without introducing additional security issues, an inter-function scheduler for scheduling containers between functions, and a sharing-aware function balancer at the cluster-level for balancing the workload across different nodes. Experiments using Azure serverless traces show that Pagurus alleviates 84.6\% of the cold startup, and the cold startup latency is reduced from hundreds of milliseconds to 16 milliseconds if alleviated.