Elixir Phoenix and "role postgres does not exist"

If you’re trying to follow along the Elixir Phoenix Up and Running guide you may run straight into this error if you’re using homebrew’s Postgres install when you run mix ecto.create

$ mix ecto.create
18:54:52.762 [error] GenServer #PID<0.292.0> terminating
** (Postgrex.Error) FATAL 28000 (invalid_authorization_specification) role "postgres" does not exist
    (db_connection 2.4.0) lib/db_connection/connection.ex:100: DBConnection.Connection.connect/2
    (connection 1.1.0) lib/connection.ex:622: Connection.enter_connect/5
    (stdlib 3.15.2) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Last message: nil
State: Postgrex.Protocol

18:54:52.773 [error] GenServer #PID<0.299.0> terminating
** (Postgrex.Error) FATAL 28000 (invalid_authorization_specification) role "postgres" does not exist
    (db_connection 2.4.0) lib/db_connection/connection.ex:100: DBConnection.Connection.connect/2
    (connection 1.1.0) lib/connection.ex:622: Connection.enter_connect/5
    (stdlib 3.15.2) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Last message: nil
State: Postgrex.Protocol
** (Mix) The database for Hello.Repo couldn't be created: killed

That’s not ideal! The core issue in that stack trace error is role "postgres" does not exist

There’s a couple of ways to fix the problem.

One: Fix the Phoenix config to match up with homebrew

Open config/dev.exs and change the config to have your username and a blank password.

By default Phoenix assumes “postgres” for the username and password.

config :hello, Hello.Repo,
  username: "sdball",
  password: "",
  database: "hello_dev",
  hostname: "localhost",
  show_sensitive_data_on_connection_error: true,
  pool_size: 10

Two: Fix the postgres config to match up with Phoenix

1. Connect to postgres

$ psql -d postgres

2. Create the “postgres” user

CREATE ROLE postgres LOGIN CREATEDB;

3. (ctrl-d) to close the connection to postgres

Things should be working!

After either fix you should be able to create the postgres database!

$ mix ecto.create

The database for Hello.Repo has been created