System and method to commit container changes on a VM-based container

1. A method for committing changes of an image of a container running in a virtual machine (VM) on a host computer system, the method comprising:

obtaining a guest starting folder containing a starting image for the container, wherein the guest starting folder resides in the virtual machine;

while the container is running the starting image, storing changes made by the container running in the virtual machine to the starting image in a first guest union folder to generate a changed image for the container, wherein the first guest union folder is a union mount of a first new guest folder and the guest starting folder, and wherein the first new guest folder reflects the changes in the first guest union folder; and

forming a second guest union folder as a union mount of a second new guest folder and the guest starting folder, the second new guest folder containing the changes to the starting image, and the second guest union folder containing the changed image.

2. The method of claim 1 ,

wherein a guest file system of the VM is shared with a host file system of the host computer system; and

wherein the host file system includes a host starting folder containing the starting image of the container and the guest starting folder is obtained from the host computer system by sharing the host starting folder as the guest starting folder in the guest file system.

3. The method of claim 2 ,

wherein the host file system includes a new host folder; and

wherein the host file system shares the new host folder as a first new guest folder of the guest file system, the first new guest folder containing the changes to the starting image.

4. The method of claim 2 , wherein a container runtime fetches the starting image for the container from the host computer system and provides the starting image in the host starting folder.

5. The method of claim 4 ,

wherein the starting image for the container resides in a repository for images on the host computer system; and

wherein the images in the repository are read-only images.

6. The method of claim 1 , wherein the changed image in the second guest union folder is stored in a repository of container images.

7. The method of claim 1 , wherein a container runtime runs on the host computer system but does not run the starting image.

8. A host computer system comprising:

one or more CPU s; and

a memory coupled to the CPUs, wherein the memory has loaded therein system software that includes virtualization software for running one or more virtual machines, and a container runtime;

wherein the system software runs the container runtime and one of the virtual machines runs a guest operating system with a container running as an application of the guest operating system; and

wherein the guest operating system is configured to:

obtain a guest starting folder containing a starting image for the container, wherein the guest starting folder resides in the virtual machine;

while the container is running the starting image, store changes made by the container running in the virtual machine to the starting image in a first guest union folder to generate a changed image for the container, wherein the first guest union folder is a union mount of a first new guest folder and the guest starting folder, and wherein the first new guest folder reflects the changes in the first guest union folder; and

form a second guest union folder as a union mount of a second new guest folder and the guest starting folder, the second new guest folder containing the changes to the starting image, and the second guest union folder containing the changed image.

9. The host computer system of claim 8 ,

wherein a guest file system of the VM is shared with a host file system of the host computer system; and

wherein the host file system includes a host starting folder containing the starting image of the container and the guest starting folder is obtained from the host computer system by sharing the host starting folder as the guest starting folder in the guest file system.

10. The host computer system of claim 9 ,

wherein the host file system includes a new host folder; and

wherein the host file system shares the new host folder as a first new guest folder of the guest file system, the first new guest folder containing the changes to the starting image.

11. The host computer system of claim 9 , wherein the container runtime fetches the starting image for the container from the host computer system and provides the starting image in the host starting folder.

12. The host computer system of claim 11 ,

wherein the starting image for the container resides in a repository for images on the host computer system; and

wherein the images in the repository are read-only images.

13. The host computer system of claim 8 , wherein the changed image in the second guest union folder is stored in a repository of container images.

14. The host computer system of claim 8 , wherein a container runtime runs on the host computer system but does not run the starting image.

15. A non-transitory computer-readable medium comprising instructions executable in a computer system, wherein the instructions when executed in the computer system cause the computer system to carry out a method for committing changes of an image of a container running in a virtual machine (VM) on a host computer system, the method comprising:

obtaining a guest starting folder containing a starting image for the container, wherein the guest starting folder resides in the virtual machine;

while the container is running the starting image, storing changes made by the container running in the virtual machine to the starting image in a first guest union folder to generate a changed image for the container,

wherein the first guest union folder is a union mount of a first new guest folder and the guest starting folder, and

wherein the first new guest folder reflects the changes in the first guest union folder; and

forming a second guest union folder as a union mount of a second new guest folder and the guest starting folder, the second new guest folder containing the changes to the starting image, and the second guest union folder containing the changed image.

16. The non-transitory computer-readable medium of claim 15 ,

wherein a guest file system of the VM is shared with a host file system of the host

computer system; and

wherein the host file system includes a host starting folder containing the starting image of the container and the guest starting folder is obtained from the host by sharing the host starting folder as the guest starting folder in the guest file system.

17. The non-transitory computer-readable medium of claim 16 ,

wherein the host file system includes a new host folder; and

wherein the host file system shares the new host folder as a first new guest folder of the guest file system, the first new guest folder containing the changes to the starting image.

18. The non-transitory computer-readable medium of claim 16 ,

wherein a container runtime fetches the starting image for the container from the host computer system and provides the starting image in the host starting folder;

wherein the starting image for the container resides in a repository for images on the host computer system; and

wherein the images in the repository are read-only images.

19. The non-transitory computer-readable medium of claim 15 , wherein the changed image in the second guest union folder is stored in a repository of container images.

20. The non-transitory computer-readable medium of claim 15 , wherein a container runtime runs on the host computer system but does not run the starting image.