We use Redis as common in-memory cache for our distributed php processes. Since it also provides message-queue functions and was already in our stack, we didn't use an alternative like RabbitMQ for async handling. We have a multi-instance setup (configured via Ansible) on our maschines. High-Availaibility is configured via Redis Sentinel and HAProxy. The HAProxy-HAProxy setup is also responsible for SSL encryption. We could not use twemproxy since not all commands our application uses are supported.