Comment 3 for bug 1872534

The cassandra charm already ends up with cqlsh installed and available, so a subordinate does not seem necessary. The cs:~cassandra-charmers/cqlshrc charm was primarily written to test the cassandra charm, and available as it might be useful to provide CLI access to a user who should not have access to the cassandra machine itself.

A suboprdinate would also need to be careful to not conflict, eg. both attempting to own the cqlshrc files in ~root. But if you have a use case I can't see why not. A subordinate would only need to handle the relation and write out authentication credentials, as the cassandra tools would already be installed. A subordinate would only get connection details to the local node due to the different relation scope, but that isn't really a problem with Cassandra as the other nodes would be discovered by the client (assuming the local Cassandra server is running).

$ juju ssh cassandra/9
Welcome to Ubuntu 18.04.4 LTS (GNU/Linux 4.15.0-96-generic x86_64)

 * Documentation: https://help.ubuntu.com
 * Management: https://landscape.canonical.com
 * Support: https://ubuntu.com/advantage

  System information as of Tue Apr 28 10:57:37 UTC 2020

  System load: 0.01 Processes: 89
  Usage of /: 20.7% of 9.52GB Users logged in: 0
  Memory usage: 77% IP address for ens2: 10.48.129.114
  Swap usage: 0%

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To run a command as administrator (user "root"), use "sudo <command>".
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ubuntu@juju-e60653-default-29:~$ cqlsh
Connected to juju at 10.48.129.114:9042.
[cqlsh 5.0.1 | Cassandra 3.11.6 | CQL spec 3.4.4 | Native protocol v4]
Use HELP for help.
jujucharm@cqlsh>