For Magento 2.3 and Elasticsearch 5.2, my system is an Ubuntu 18/04 with 2GB of RAM, is this RAM enough? (I have 6000 products more or less)
Magento lists 2GB RAM as the minimum requirement: https://devdocs.magento.com/guides/v2.3/install-gde/system-requirements-tech.html
The problem ist that you should also set a minimum
memory_limit of 512MB in your php.ini. This would mean that if you only 2GB RAM, you might run into memory issues.
Is the MySQL database also running on the same server? Because then it's not enough at all.
I would only run Magento 2 on a server that has at least 16GB of RAM. The actual usage does not only depend on your catalog size, but also how many websites/stores you have, how many visitors to your website etc.