Why I can't send an api request to database on heroku? - node.js

Question

I have an app built with react, redux, node, and postgresql(knex), and I could deploy this app to heroku. However, all the api requests to database made in an app does not work. It is not fetching any data or I can not sign up.
In the app, I get a console error like this:
Failed to load resource: the server responded with a status of 503 (Service Unavailable)
Uncaught (in promise) Error: Request failed with status code 503(…)
...
Is there a way to fix this?
My knex configuration:
module.exports = {
development: {
client: 'postgresql',
connection: {
database: 'database5',
user: 'user',
password: ''
},
pool: {
min: 2,
max: 10
},
migrations: {
tableName: 'knex_migrations'
}
},
staging: {
client: 'postgresql',
connection: {
database: 'my_db',
user: 'username',
password: 'password'
},
pool: {
min: 2,
max: 10
},
migrations: {
tableName: 'knex_migrations'
}
},
production: {
client: 'postgresql',
connection: process.env.DATABASE_URL,
pool: {
min: 2,
max: 10
},
migrations: {
tableName: 'knex_migrations'
}
}
};
Error in heroku logs:
2016-10-25T13:06:04.647342+00:00 app[web.1]: Unhandled rejection Error: connect ECONNREFUSED 127.0.0.1:5432
2016-10-25T13:06:04.647361+00:00 app[web.1]: at Object.exports._errnoException (util.js:893:11)
2016-10-25T13:06:04.647362+00:00 app[web.1]: at exports._exceptionWithHostPort (util.js:916:20)