Provide SSL certificate to PostgreSQL in a Rails app

I have a Rails app using an Amazon RDS PostgreSQL instance.

I'd like pg to use SSL to connect to this DB.

Following http://ift.tt/1Bxw8jW[...], I saved rds-combined-ca-bundle.pem at /config/ca/rds.pem and my database.yml looks like this:

production:
  adapter: postgresql
  database: <%= ENV['DB_NAME'] %>
  username: <%= ENV['DB_USERNAME'] %>
  password: <%= ENV['DB_PASSWORD'] %>
  host: <%= ENV['DB_ADDRESS'] %>
  port: <%= ENV['DB_PORT'] %>
  sslmode: 'verify-full'
  sslrootcert: 'config/ca/rds.pem'

But I have no idea if it's really using SSL: I can change sslrootcert path to anything, and my app is still up. What am I missing?