This page contains the list of deprecations and important or breaking changes for Vault 1.3.0 compared to 1.2.4. Please read it carefully.
Secondary cluster activation
There has been a change to the way that activating performance and DR secondary clusters works when using public keys for encryption of the parameters rather than a wrapping token. This flow was experimental and never documented. It is now officially supported and documented but is not backwards compatible with older Vault releases.
Cluster cipher suites
On its cluster port, Vault will no longer advertise the full TLS 1.2 cipher suite list by default. Although this port is only used for Vault-to-Vault communication and would always pick a strong cipher, it could cause false flags on port scanners and other security utilities that assumed insecure ciphers were being used. The previous behavior can be achieved by setting the value of the (undocumented) cluster_cipher_suites config flag to tls12.