Hi. Is it possible to enable Basic Auth on ES without SSL? I couldn't find that info.
We're configuring SSL at the edge of our cluster and enabling SSL beyond that between services is not a requirement for us.
Not sure, those are a mandatory boostrap checks when starting your cluster
if security is enabled then you must have SSL/TLS, except if your cluster is a single node 
check it here
I see. Thanks for the answer.
You are required to have SSL between nodes (the transport port that defaults to 9300).
You can use the elasticsearch-certutil tool to set that up with a cluster-specific CA, with very minimal effort or impact on your cluster.
You are not required to configure SSL for the REST interface (the http port that defaults to 9200).