Prevent downtime using lftp mirror - deployment

Question

I'm using lftp to deploy a website via Travis CI. There is a build process before the deployment, for that reason a build directory is present and pushed to the root of the ftp server.
lftp $FTP_URL -e "glob -d mirror build . --reverse --delete-first --parallel=10 && exit"
It works quite well, but I dislike to have a downtime / temporary PHP parse errors because of missing files on my website. What is the best way to work arround that issue?
My first approach was an option to set a temporary directory, but the lftp man page says there is only a options for temporary files. I still tried the option but it didn't help.
My second approach was to use "mirror build temp" to use a temporary folder and then replace the root with it. The problem here is, that I cannot exclude the temp folder while deleting the old files and folders like rm -rf *.

Answer 1

For small changes not involving adding/removing php files set xfer:use-temp-file should be sufficient. Also don't use --remove-first, as it causes lftp to delete obsolete files before uploading.
For larger changes I'd create a separate directory for each version of the site and redirect the web server to the directory using .htaccess mod_rewrite or some other configuration file. This technique will allow atomic switch to the new version (and back if needed). Besides, you will be able to do final pre-production testing of the new version if you redirect to the new version conditionally based on your IP address or using some other rule.
If you don't want to re-upload whole site for each new version and the FTP server supports FXP with itself, then you can copy old version to a new directory using mirror old_directory ftp://user#example.com/new_directory, then update the new directory using mirror -eR local_dir new_directory.

Answer 2

This is a zero downtown pattern - each placeholder should be replaced:
lftp $FTP_URL -e "mirror {SOURCE} {TARGET}-new-{TIMESTAMP} --reverse --delete-first;
mv {TARGET} {TARGET}-old-{TIMESTAMP};
mv {TARGET}-new-{TIMESTAMP} {TARGET};
rm -rf {TARGET}-old-{TIMESTAMP};
exit"