Create Session symlink to shared Session folder.

Deployment-Example.php

// create Session folder and symlink it to the shared folder.
$deployment->onInitialize(function () use ($workflow, $application) {
    $workflow->setTaskOptions('typo3.surf:generic:createDirectories', array('directories' => array('shared/Data/Session')));
    $workflow->setTaskOptions('typo3.surf:generic:createSymlinks', array(
        'symlinks' => array(
            'Data' => '../../../shared/Data/Session/'
        )
    ));
});