Aurora PostgreSQL Blue/Green with custom parameter groups requires a pre-created Green parameter group

When creating a Blue/Green deployment with a major version upgrade (e.g. PG 16 → 17) on an Aurora PostgreSQL cluster that uses a custom parameter group, you get:

Output

InvalidParameterCombination: The current DB cluster parameter group
bg-test-apg16-params is custom. You must explicitly specify a new DB cluster
parameter group, either default or custom, for the engine version upgrade

Pre-create a parameter group for the Green environment and pass it via --target-db-cluster-parameter-group-name:

Terminal

aws rds create-db-cluster-parameter-group \
  --db-cluster-parameter-group-name my-pg17-params \
  --db-parameter-group-family aurora-postgresql17 \
  --description "Params for PG17 green environment"
 
aws rds create-blue-green-deployment \
  --source arn:aws:rds:...:cluster:my-cluster \
  --target-engine-version 17.6 \
  --target-db-cluster-parameter-group-name my-pg17-params

Aurora MySQL doesn't have this issue — it can create the Green environment with the default parameter group. This is PostgreSQL-specific.