TYPO3 Core

I would also be interested in such a feature.

https://extensions.typo3.org/extension/tm_masterslave

This is the extension.
I will write un simple configuation README

This is how we solved it:

class PrimaryReplicaConnection extends \TYPO3\CMS\Core\Database\Connection
{
    public function connect(): bool
    {
        $allParams = $this->getParams();
        try {
            return parent::connect();
        } catch(\Doctrine\DBAL\Exception\ConnectionException $e) {
            if (!isset($allParams['replica'])) {
                throw $e;
            }
        }
        while ($nextReplica = array_shift($allParams['replica'])) {
            $allParams = array_replace_recursive($allParams, $nextReplica);
            $driverOptions = $allParams['driverOptions'] ?? [];
            $user          = $allParams['user'] ?? null;
            $password      = $allParams['password'] ?? null;
            try {
                $this->_conn = $this->_driver->connect($allParams, $user, $password, $driverOptions);
                if ($this->_eventManager->hasListeners(\Doctrine\DBAL\Events::postConnect)) {
                    $eventArgs = new \Doctrine\DBAL\Event\ConnectionEventArgs($this);
                    $this->_eventManager->dispatchEvent(\Doctrine\DBAL\Events::postConnect, $eventArgs);
                }
                return true;
            } catch(\Doctrine\DBAL\Exception\ConnectionException $e) {
                continue;
            }
        }
        // No connection available
        if ($e) {
            throw $e;
        }
    }
}

and in AdditionalConfiguration.php

        $GLOBALS['TYPO3_CONF_VARS']['DB']['Connections']['Default']['host'] = getenv('DB_HOST_NODE1') ?: getenv('TYPO3_DB_HOST');
        $GLOBALS['TYPO3_CONF_VARS']['DB']['Connections']['Default']['dbname'] = getenv('DB_NAME') ?: getenv('TYPO3_DB_DATABASE');
        $GLOBALS['TYPO3_CONF_VARS']['DB']['Connections']['Default']['user'] = getenv('DB_USER') ?: getenv('TYPO3_DB_USERNAME');
        $GLOBALS['TYPO3_CONF_VARS']['DB']['Connections']['Default']['password'] = getenv('DB_PASSWORD') ?: getenv('TYPO3_DB_PASSWORD');
        $GLOBALS['TYPO3_CONF_VARS']['DB']['Connections']['Default']['replica'] = [
            ['user' => getenv('DB_USER'), 'password' => getenv('DB_PASSWORD'), 'host' => getenv('DB_HOST_NODE2'), 'dbname' => getenv('DB_NAME')],
            ['user' => getenv('DB_USER'), 'password' => getenv('DB_PASSWORD'), 'host' => getenv('DB_HOST_NODE3'), 'dbname' => getenv('DB_NAME')],
        ];
        $GLOBALS['TYPO3_CONF_VARS']['DB']['Connections']['Default']['wrapperClass'] = \PrimaryReplicaConnection::class;