s3sync is concurrent s3 uploader.
gradle build
$HOME/.s3sync
{
"access_key": "XXX",
"secret_key": "XXX"
}
java -jar ./build/libs/s3sync-1.0.jar -P -c $HOME/.s3sync --header "Cache-Control: public, max-age=86400" --concurrent 50 --dir /path/to/upload/directory --bucket s3://BUCKET_NAME/path/to/directory