title: AWS PostgreSQL `Cannot find version X for aurora`
body: <p>Similar to <a href="https://stackoverflow.com/questions/49506126/error-creating-db-instance-invalidparametercombination-cannot-find-version-5-6">Error creating DB Instance: InvalidParameterCombination: Cannot find version 5.6.10a for aurora-mysql</a> but for Postgres, which has a different cause.</p>
  <pre><code>* error creating RDS Cluster (mycompany-pulumi-aurora-cluster) Instance: InvalidParameterCombination: Cannot find version 12.6 for aurora
      status code: 400, request id: someid
  </code></pre>
  <p>But 12.6 is valid for Aurora PostgreSQL in that region:</p>
  <pre><code>$ aws rds describe-db-engine-versions --engine aurora-postgresql --query '*[].[EngineVersion]' --output text --region us-east-2
  9.6.3
  9.6.6
  9.6.8
  9.6.9
  9.6.11
  9.6.12
  9.6.16
  9.6.17
  9.6.18
  9.6.19
  9.6.21
  10.4
  10.5
  10.6
  10.7
  10.11
  10.12
  10.13
  10.14
  10.14
  10.16
  11.4
  11.6
  11.7
  11.8
  11.9
  11.11
  12.4
  12.6
  </code></pre>