When you create a role you specify which indices each role can access, this is explained in the role management documentation linked above.
If this will work for you depends on how you are organizing your data in the indices, if you have multiple clients you have basically two options:
- Use indices per client, something like
clientName-indiceName-*, then in the role for this client you will give access to all indices starting withclientName-*. - Use document level security, but this is more complex and it is a paid feature, so it doesn't work with the basic free license.
Please read the linked documentation from the previous posts.
Also, you didn't provide any information about what kind of service you are providing to your clients and how you are providing it, I would suggest that you open a new topic if you have more questions about it, also, check the Elastic license to see if what you are doing is allowed.