PostgreSQL: create read only user

Source: How to Create a Read-Only Database User in Postgres for Analytics and Reporting

createuser -U postgres -D -R -S aws_user

alter user aws_user with encrypted password 'MY PASSWORD';
grant connect on database dwhmbqt to aws_user;

do
$$
declare
 _query text;
 _schema text;
begin
 for _schema in select nspname from pg_namespace where nspname ~ '_db$' loop
   _query := format('grant usage on schema %I to aws_user', _schema);
   raise notice '%', _query;
    execute _query;
 end loop;
end;
$$

do
$$
declare
 _query text;
 _schema text;
begin
 for _schema in select nspname from pg_namespace where nspname ~ '_db$' loop
  _query := format('grant select on all tables in schema %I to aws_user', _schema);
  raise notice '%', _query;
   execute _query;
 end loop;
end;
$$

Then in pg_hba.conf:

host    dwhmbqt         aws_user           10.192.0.0/16   md5