Docker Image Sharing in Distributed Fog Infrastructures

Fog computing platforms offer virtualized resources located in the vicinity of their end users. Their broad geographical distribution force them to split physical resources in large numbers of relatively weak machines. The limited available disk space per fog node however creates problems for Docker-based systems which locally cache a copy of every container image they execute: first, caches may fill very quickly, whereas standard Docker never automatically evicts any image from its cache. This motivates us to implement automatic cache replacement in Docker. Second, splitting cache space in multiple disjoint partitions negatively impacts the hit rates. This motivates us to propose allowing multiple co-located Docker servers to share their caches. Our trace-based evaluations show that the proposed design achieves significant cache hit improvements, leading to reductions of average container deployment times between 37% and 78% depending on the scenarios.