Create new cores in SOLR via HTTP?

Yes, you can create the Solr cores via HTTP. You have found the correct URL (https://wiki.apache.org/solr/CoreAdmin) to look into. All the above parameters are optional.

instanceDir - This is the path where your new core will be created. It'll create the folder structure provided by you, under "/example/solr/". If you don't provide this parameter, it'll automatically create a new core (with the collection no) like collection1.

config - If you want to have a different solrconfig.xml for the new core, then provide this. Otherwise, it'll share the existing core's (collection1) config by default.

schema - If you want to have a different schema.xml for the new core, then provide this. Otherwise, it'll share the existing core's (collection1) schema by default.

dataDir - This is the path where your new core's data will be stored. It'll create the folder structure provided by you under the new core folder.

If you really don't want some different configuration for your new core, follow the sample HTTP URL

http://localhost:8983/solr/admin/cores?action=CREATE&name=core_name&numShards=2&replicationFactor=2

Hope this will help.

Copy the configsets folder recursively to var/solr/data/your_new_core_name then add the your_new_core_name from the admin panel

The configsets path usually should be here.

/solr-8.6.3/server/solr/configsets/_default/conf

I had the exact same issue and I was not able to make it work from the description on https://wiki.apache.org/solr/CoreAdmin#CREATE

What solved it for me was updating to Solr 5 and using a configSet (introduced in 4.8) which defines the shared solrconfig/schema. The following URL can be used to create several cores with the same configuration:

http://localhost:8983/solr/admin/cores?action=CREATE&name=new_core&configSet=basic_configs

The 'basic_configs' is the name of a configSet that comes with the Solr 5 download (solr-5.0.0/server/solr/configsets/basic_config). The URL worked out-of-the-box after starting the Solr server.

https://cwiki.apache.org/confluence/display/solr/Config+Sets