How to setup cross region replica of AWS RDS for PostgreSQL

Question

I have a RDS for PostgreSQL setup in ASIA and would like to have a read copy in US.

But unfortunately just found from the official site that only RDS for MySQL has cross-region replica but not for PostgreSQL.

And I saw this page introduced other ways to migrate data in to and out of RDS for PostgreSQL.

If not buy an EC2 to install a PostgreSQL by myself in US, is there any way the synchronize data from ASIA RDS to US RDS?

Answer 1

It all depends on the purpose of your replication. Is it to provide a local data source and avoid network latencies ?

Assuming that your goal is to have cross-region replication, you have a couple of options.

Custom EC2 Instances

You can create your own EC2 instances and install PostgreSQL so you can customize replication behavior.

I've documented configuring master-slave replication with PostgreSQL on my blog: http://thedulinreport.com/2015/01/31/configuring-master-slave-replication-with-postgresql/

Of course, you lose some of the benefits of AWS RDS, namely automated multi-AZ redundancy, etc., and now all of a sudden you have to be responsible for maintaining your configuration. This is far from perfect.

Two-Phase Commit

Alternate option is to build replication into your application. One approach is to use a database driver that can do this, or to do your own two-phase commit. If you are using Java, some ideas are described here: JDBC - Connect Multiple Databases

Use SQS to uncouple database writes

Ok, so this one is the one I would personally prefer. For all of your database writes you should use SQS and have background writer processes that take messages off the queue.

You will need to have a writer in Asia and a writer in the US regions. To publish on SQS across regions you can utilize SNS configuration that publishes messages onto multiple queues: http://docs.aws.amazon.com/sns/latest/dg/SendMessageToSQS.html

Of course, unlike a two phase commit, this approach is subject to bugs and it is possible for your US database to get out of sync. You will need to implement a reconciliation process -- a simple one can be a pg_dump from Asian and pg_restore into US on a weekly basis to re-sync it, for instance. Another approach can do something like a Cassandra read-repair: every 10 reads out of your US database, spin up a background process to run the same query against Asian database and if they return different results you can kick off a process to replay some messages.

This approach is common, actually, and I've seen it used on Wall St.

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So, pick your battle: either you create your own EC2 instances and take ownership of configuration and devops (yuck), implement a two-phase commit that guarantees consistency, or relax consistency requirements and use SQS and asynchronous writers.

Answer 2

This is now directly supported by RDS.

Example of creating a cross region replica using the CLI:

aws rds create-db-instance-read-replica \
    --db-instance-identifier DBInstanceIdentifier \
    --region us-west-2 \
    --source-db-instance-identifier arn:aws:rds:us-east-1:123456789012:db:my-postgres-instance