Yes it is correct that asynchronous replication is the only way Redis handles replication, however replication and durability are still in topic: if the master burns in fire, the slave will contain your data ;)
However there are people that turn Redis async replication into synchronous replication with a trick: they perform:
MULTI
SET foo bar
PUBLISH foo:ack 1
EXEC
Because PUBLISH is propagated to the slave if they are listening with another connection to the right channel they'll get the ACK from the slave once the write reached the slave. Not always practical but it's an interesting trick.
However there are people that turn Redis async replication into synchronous replication with a trick: they perform:
Because PUBLISH is propagated to the slave if they are listening with another connection to the right channel they'll get the ACK from the slave once the write reached the slave. Not always practical but it's an interesting trick.