Implementing read replicas in various data center facilities (Availability Zones) not only spreads the load of customer queries across multiple sources but also ensures that the application can failover to other replicas in case of an outage. This is the most effective solution to address both read traffic performance and availability concerns without changing the primary data source configuration. Adding indexes may improve query performance but will not address the potential for an outage. Making the database instance larger will increase overall capacity but is a less targeted solution for read scalability and does not provide multi-facility resilience. Enabling cross-region replication adds geographical distribution but could introduce additional latency for the reads and doesn't address the immediate need to spread the read load.