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The <code>crtools</code> utility can be used to perform live migration of apps or containers. This page is a sort of HOWTO describing this.
The <code>crtools</code> utility can be used to perform live migration of apps or containers. This page is a sort of HOWTO describing this.
== Migration sequence ==
In order to live-migrate an application or a container you should make sure, that files, that are/can be accessed by processes you're migrating are available on both nodes -- source and destination. This can be achieved by using either shared file-system such as NFS, GlusterFS or CEPH, or by using <code>rsync</code> to copy files from one box to another. Further in this article we assume, that the file-system is the same on both sides.
In order to live-migrate an application or a container you should make sure, that files, that are/can be accessed by processes you're migrating are available on both nodes -- source and destination. This can be achieved by using either shared file-system such as NFS, GlusterFS or CEPH, or by using <code>rsync</code> to copy files from one box to another. Further in this article we assume, that the file-system is the same on both sides.
In order to live migrate tasks you should do these steps:
=== Dump ===
Take tasks you're about to migrate and dump them into some place, asking <code>crtools</code> to leave them in stopped state after dump:
[src]# crtools dump --tree <pid> --images-dir <path-to-existing-directory> --leave-stopped
The directory you put images to can reside on the shared file-system if you're using one. In this case you can skip the Copy step and proceed to Restore.
=== Copy ===
Copy images to destination node:
[src]# scp -r <path-to-images-dir> <dst-node>/<path-to-images>
# crtools dump --tree <pid> --images-dir <path-to-existing-directory> --leave-stopped
=== Restore ===
Go to the destination node and restore the apps from images on it:
[dst]# crtools restore --tree <pid> --images-dir <path-to-images>
# crtools restore --tree <pid> --images-dir <path-to-images>
=== Kill ===
If everything went OK you can return on the source node and kill stopped tasks on it.
== Notes ==
The directories with images would contain two copies of applications memory, which may be space-consuming. The CRIU can perform [[disk-less migration]] to address this.
The directories with images would contain two copies of applications memory, which may be space-consuming. The CRIU can perform [[disk-less migration]] to address this.