277
edits
Changes
Jump to navigation
Jump to search
mLine 1:
Line 1: − Please, read the article about [[Live migration]] before this one.+ − This page describes how to reduce the freeze time of an application by using the [[memory changes tracking]] ability.+ − + − + + + + + − + + − + − + − + − + + + + + + + − Go to the destination node and restore the apps from images on it:+ − + − + + + + + + +
→Restore: Using -t with criu restore is obsoleted
This page describes how to reduce the freeze time of an application by using the [[memory changes tracking]] ability to perform [[wikipedia:Live_migration#Pre-copy_memory_migration|pre-copy memory migration]].
{{Note|It is assumed that you already read [[Live migration]] article before this one.}}
== Migration sequence ==
== Migration sequence ==
The steps below look like those in regular live migration, but include one of more pre-dump stages.
The steps below look like those in regular live migration, but include one or more pre-dump stages.
=== Pre-dump ===
=== Pre-dump ===
Take tasks you're about to migrate and pre-dump them into some place. Tasks will remain running after pre-dump, unlike regular dump.
Take tasks you are about to migrate and pre-dump them into some place. Tasks will remain running after pre-dump, unlike regular dump.
[src]# criu pre-dump --tree <pid> --images-dir <path-to-existing-directory-A>
[src]# criu pre-dump --tree <pid> --images-dir <path-to-existing-directory-A>
The directory with images can be on a shared storage, or you can use [[disk-less migration]] to avoid the '''Copy''' step.
The directory with images can be on a shared storage, or you can use [[disk-less migration]] to avoid the '''Copy''' step.
Now you can either proceed to next step and do regular dump, or perform the pre-dump step again. In the latter case pre-dump would generate another set of pre-dump images which will contain memory changed after previous pre-dump. Doing several pre-dump iterations may reduce the amount of data dumped on dump stage and thus lead to shorter freeze time.
Note, that if you're going to perform more than one pre-dump steps, you should create different directories for images and properly reference them with the <code>--images-dir</code> and the <code>--prev-images-dir</code> for all pre-dump and dump steps.
=== Dump ===
=== Dump ===
Now you can do regular dump of your processes.
Now you can do regular dump of your processes.
[src]# criu dump --tree <pid> --images-dir <path-to-existing-directory-B> --prev-images-dir <path-to-directory-A-relative-to-B> --leave-stopped
[src]# criu dump --tree <pid> --images-dir <path-to-existing-directory-B> \
--prev-images-dir <path-to-directory-A-relative-to-B> --leave-stopped --track-mem
Note, that
Note that:
# this dump would work faster, than it would if there were no the pre-dump stage, as this dump only takes the memory that has changed, since the pre-dump step.
# this dump would work faster than without pre-dump, as this dump only takes the memory that has changed since the last pre-dump;
# the <code>--prev-images-dir</code> should contain path to the directory with pre-dump images ''relative to the directory where the dump images will be put''
# the <code>--prev-images-dir</code> should contain path to the directory with pre-dump images ''relative to the directory where the dump images will be put''.
=== Copy ===
=== Copy ===
Copy images to destination node:
Copy images to the destination node:
[src]# scp -r <path-to-images-dir> <dst>:/<path-to-images>
[src]# scp -r <path-to-images-dir> <dst>:/<path-to-images>
or using rsync
[src]# rsync -rl <path-to-images-dir>/ <dst>:<path-to-images>
Note: It is important to enable "copy symlinks as symlinks" (<code>-l</code> for <code>rsync</code>) to ensure that symlinks are preserved between previous directories. When <code>-r</code> is passed to <code>scp</code> it will follow symbolic links encountered in the tree traversal.
=== Restore ===
=== Restore ===
On the destination node restore the apps from images:
[dst]# criu restore --tree <pid> --images-dir <path-to-images>
[dst]# criu restore --images-dir <path-to-images>
=== Kill ===
=== Kill ===
If everything went OK you can return on the source node and kill stopped tasks on it.
If everything went OK you can kill stopped tasks on the source node:
[src]# FIXME put command here
[src]# FIXME put command here
== Further reading ==
* [[P.Haul]] is the Go extension to CRIU doing [[live migration]]
[[Category: HOWTO]]
[[Category: HOWTO]]
[[Category: Memory]]
[[Category: Live migration]]