The optional routing_strategy configuration option was added. The available values are first-available, next-available, round-robin, and round-robin-with-fallback.

Previously, these strategies were described as scheduling modes by the mode configuration option where the read-write mode defaults to the first-available strategy, and the read-only mode defaults to the round-robin strategy. This preserves previous behavior for these modes.

The --ssl-key and --ssl-cert optional bootstrap command-line options were added. They directly use their MySQL client's counterparts, and specify the client-side certificate and private key to facilitate client-side authentication. This is useful when the root account used during bootstrap was created with REQUIRE X509, which requires the client to authenticate itself when logging in.

The new connect_timeout and read_timeout metadata configuration file options were added. These are defined under the [DEFAULT] namespace and affect internal operations, such as metadata server connections.

Bootstrap now accepts any member of an InnoDB cluster and automatically finds and reconnects to a writable primary. Before, only the primary was accepted.

Bootstrap now accepts the --config option and reads the [logger] level option's definition.

The maximum number of concurrent client connections was increased from about 500 to over 5000, a limit now dependent on the operating system. To achieve this, select()-based fd event calls were replaced by poll() (or WSAPoll() on Windows).

MySQL Router 8.0.22 increased this limit to about 50,000; see the [IO] backend and threads configuration options for details.

A new mysqlrouter_plugin_info utility was added to help debug MySQL Router plugins. It provides information such as the plugin version, description, ABI version, requirements, and function pointers.