read replicas with legacy code that doesn't properly separate queries

Question

For applications that are not built to use read replicas and send writes to a master connection, is there an option to have the read replicas pass on all write queries while handling reads themselves?  
  
The multi-master mode might work for this but it sounds risky if the code doesn't divide writes between the nodes to avoid conflicts.

Answer

I was working on read-write separation (Aurora 4 MySQL) for quite some time and as far as I can tell read replicas do not have such an option.   
  
If the implementation of query routing is not an option, then you may consider using third-party RW splitters, like ProxySQL, Apache Sharding Sphere (https://shardingsphere.apache.org/document/current/en/features/read-write-split/) or   
Heimdall proxy (https://aws.amazon.com/blogs/apn/using-the-heimdall-proxy-to-split-reads-and-writes-for-amazon-aurora-and-amazon-rds/).  
  
HTH

Answer

Excellent options, thanks!

read replicas with legacy code that doesn't properly separate queries

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