I'm afraid that you can't.
The instructions that you followed do not keep a copy of the CA key, so it is not possible to add new certificates.
I'll see what I can do to update that blog post with a warning, or additional instructions to retain the CA key, because I do not recommend creating a throw-away CA like that.
Thank you for the reply. It means to me that I have to recreate the CA (now with --keep-ca-key parameter) and certificates/keys and exchange all certificates and keys on the ELK nodes.
After that i can use ca.crt and ca.key file to create new certificates/keys for example for beats or new cluster nodes.
Can you explain why you "do not recommend creating a throw-away CA like that".
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