Redis is used to synchronize data between traffic switch instances. It stores information about used resources (e.g gateways capacity limits) to provide correct limitation among all nodes for distributed installations.
# apt update && apt install redis-server
Try to enter redis console from traffic switch host (redis installed at the same host with traffic switch in this example):
# redis-cli 127.0.0.1:6379> ping PONG 127.0.0.1:6379> quit