How is working "ynh_backup --is_big"?

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Indeed, not a clear part of the backup.
Many modifications happened on this matter.

We were, a not so long time ago, using backup_core_only as a config set into the settings.yml of an app.
But it was source of many issues when the backup wasn’t properly done. We were ending up with the setting still in the config and still used for all backup. Even when not willing to.

So, here the current status of that, which is quite stable.

  • An user can set the setting do_not_backup_data to 1 into the config of an app to prevent data to be backed up by the backup script at any moment.
    This is an action from an user, which will affect all backups made for the app.
    (Side note, this should be into a config-panel)

  • Otherwise, the main use case of creating a backup without data is the backup made before the upgrade of the app.
    The helper ynh_backup_before_upgrade does set the environment variable BACKUP_CORE_ONLY to 1 when doing the backup.
    BACKUP_CORE_ONLY=1 does the same thing as do_not_backup_data, but it affects only the current shell. So this variable can be used to force a backup without data, but does not affect subsequent backup afterward.

Aside of the helper itself, this variable is useful for personal backup scripts.

  • Finally, the argument is_big is to be used with the helper ynh_backup to specify into your app backup script, which part of the backup is considered as potentially big data an user could not want to backup.
    Be careful though that, as this part of your app may not be backed up, you should not remove it either in your remove script.
    Otherwise, a failed upgrade will remove the data and restore the app without it ! Not cool !
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