Trusting certificates

When configuring a client to connect to a TLS server with a serving certificate that is signed by a private CA, you will need to provide the client with the CA certificate in order for it to verify the server. ca.crt will likely contain the certificate you need to trust, but do not mount the same Secret as the server to access ca.crt. This is because:

That Secret also contains the private key of the server, which should only be accessible to the server. You should use RBAC to ensure that the Secret containing the serving certificate and private key are only accessible to Pods that need it.
Rotating CA certificates safely relies on being able to have both the old and new CA certificates trusted at the same time. See the FAQ for more details.

When configuring the client you should independently choose and fetch the CA certificates that you want to trust. Download the CA out of band and store it in a Secret or ConfigMap separate from the Secret containing the server's private key and certificate.

trust-manager can be used to manage these certificates and automatically distribute them to multiple namespaces.

This ensures that if the material in the Secret containing the server key and certificate is tampered with, the client will fail to connect to the compromised server.

The same concept also applies when configuring a server for mutually-authenticated TLS; don't give the server access to Secret containing the client certificate and private key.