After enabling Elasticsearch6+ as Catalog Search engine in Magento admin (M2.3.3) I'm receiving this error while reindexing:
Catalog Search indexer process unknown error: null
3 Answers
This was caused by the fact that I had not set a prefix for Elasticsearch in the magento admin configurations.
After setting magento2 as the value for the prefix the indexing started working.
Run below command
$ curl -XPUT -H "Content-Type: application/json" http://localhost:9200/_all/_settings -d '{"index.blocks.read_only_allow_delete": null}'
and then run
$ php bin/magento indexer:reindex
/etc/apache2/sites-available/elasticsearch.conf
=> paste this code
<VirtualHost *:8080>
ProxyPass "/" "http://localhost:9200/"
ProxyPassReverse "/" "http://localhost:9200/"
</VirtualHost>
sudo a2ensite elasticsearch.conf