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Question
How can I customize CR's image using overlay feature?
Environment
OnApp with Cloudboot CRs
Answer
Overlay is an early boot feature which allows to overlay cloudboot image with any customized hardware drivers to be executed before the IS service is started.
Please note that this doesn't apply cleanly to NIC drivers, though the NIC drivers have to load first in order to access the CP NFS resource. So, they are embedded in the cloudboot ramdisk image.
All customization files are stored on the CP server. You can find them following the next path:
/tftpboot/images/centos5/diskless/snapshot/<CR_mac_addr_dir>/overlay/
For example:
/tftpboot/images/centos5/diskless/snapshot/90-e2-ba-73-8a-00/overlay/
All tree structure after directory <overlay> will be automatically copied to the CR's "/" after the next reboot.
When moving out these files (because of the failures occurring when starting the IS daemons), please test them by reapplying on one of CRs one by one as long as they may contain important customization which is needed for appropriate work of the storage network, benchmarks, etc. It will allow to determine which files are problematic towards the IS functionality.
Here is another article that describes how to load drivers using the overlay feature here.
Please note that some specified files/scripts which had been applied trough overlay, may not work properly after the next ramdisk updating and even can lead to the system crash on booting.