Image file optimizations by opportunistic sharing

A non-transitory computer readable medium comprising instructions to be executed in a computing device to cause the computing device to carry out a method of fetching container images in a clustered container host system with a shared storage device, wherein hosts include a virtualization software layer that support execution of virtual machines in the hosts, and one or more virtual machines has implemented therein a container engine that supports execution of containers within the respective virtual machines, said method comprising:

• in connection with deploying a first container in a first virtual machine, creating a first virtual disk in the shared storage device, storing an image of the first container in the first virtual disk, mounting the first virtual disk to the first virtual machine, and updating a metadata cache to associate the image of the first container to the first virtual disk;
• and
• in connection with deploying a second container in a second virtual machine, checking the metadata cache to determine that a portion of the image of the second container is stored in the first virtual disk, creating a second virtual disk in the shared storage device, adding a reference to the first virtual disk in a metadata of the second virtual disk, and mounting the second virtual disk to the second virtual machine.