of tasks, and the overall resource utilizations for finishing the tasks, managed by FFD and HA, within their respective deadlines, respectively.

For completing Gaia and NASA tasks within their respective deadlines, respectively, as shown in Fig. \[rentcost\], HA consumes less 16.2%-76% cost than FFD for leasing VMs from public cloud. While HA postpones the finish time of these tasks to 11.8%-82.6% later, as shown in Fig. \[makespan\], compared with FFD, with completing the tasks within their respective deadlines. The less rent cost and longer finish time of HA imply that HA makes better use of resources, compared with FFD. From Fig. \[utilization\], we can see that the resource utilization of HA is 47.3%-182.8% more than that of FFD. These can be explained as follows. FFD schedules longest task first, and thus there will be small tasks left to be scheduled after assigning most of tasks. For finishing the left small tasks within their respective deadlines, only a few small tasks are assigned to one rented VM. Therefore, these VMs running only small tasks are under-utilised as rented VMs are charged by unit time, leading to high costs and low utilizations. While HA schedules the task closest to its deadline first, 