Step 1
wget -qO - https://artifacts.elastic.co/GPG-KEY-elasticsearch | sudo apt-key add -
elastic.co/guide/en/elasticsearch/reference/7.9/deb.html#deb-key
Step 2
aptitude install apt-transport-https
elastic.co/guide/en/elasticsearch/reference/7.9/deb.html#deb-repo
Step 3
Add to /etc/apt/sources.list:
deb https://artifacts.elastic.co/packages/7.x/apt stable main
elastic.co/guide/en/elasticsearch/reference/7.9/deb.html#deb-repo
Step 4
aptitude update
aptitude install elasticsearch
elastic.co/guide/en/elasticsearch/reference/7.9/deb.html#deb-repo
Step 5
update-rc.d elasticsearch defaults 95 10
service elasticsearch start
elastic.co/guide/en/elasticsearch/reference/7.9/deb.html#deb-running-init
Step 6
bin/magento indexer:reindex catalogsearch_fulltext
bin/magento cache:clean
devdocs.magento.com/guides/v2.3/config-guide/elasticsearch/es-config-nginx.html#es-reindex