A question regarding MySQL master-slave replication
For some use-cases, the (usually) small delay before the data appears on the slave isn't a problem. 

For "critical" reads, you could send them to the master only.

Another solution would be to use so-called synchronous replication, though actual synchronous replication doesn't really exist. The technology used in Galera Cluster (used by MariaDB Cluster and Percona XtraDB Cluster) is virtually synchronous. The same is true for MySQL's InnoDB Cluster.