Install postgresql packages

postgresql11.x86_64
postgresql11-devel.x86_64
postgresql11-libs.x86_64
postgresql11-server.x86_64

# yum install https://download.postgresql.org/pub/repos/yum/reporpms/EL-7-x86_64/pgdg-redhat-repo-latest.noarch.rpm
# yum install postgresql11 postgresql11-devel postgresql11-libs postgresql11-server

Set PATH

# echo 'export PATH=/usr/pgsql-11/bin:$PATH' >> /home/<your user>/.bash_profile
# echo 'export PATH=/usr/pgsql-11/bin:$PATH' >> $HOME/.bash_profile
# export PATH=/usr/pgsql-11/bin:$PATH

Initialize database

# postgresql-11-setup initdb

Edit /var/lib/pgsql/11/data/pg_hba.conf

# sed -i -E '/^#/!s/^/#/g' /var/lib/pgsql/11/data/pg_hba.conf
# echo "local   all   postgres                    trust" >> /var/lib/pgsql/11/data/pg_hba.conf
# echo "host    all   postgres    127.0.0.1/32    trust" >> /var/lib/pgsql/11/data/pg_hba.conf

Start service

# systemctl enable postgresql-11.service
# systemctl start postgresql-11.service

Create rails app

# su - <your user>
$ rails new <app name> --database=postgresql

Edit config/database.yml

Add host, port, and username:

default: &default
  adapter: postgresql
  encoding: unicode
  # For details on connection pooling, see Rails configuration guide
  # https://guides.rubyonrails.org/configuring.html#database-pooling
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  host: 127.0.0.1
  port: 5432
  username: postgres

Comment out username and password

production:
  <<: *default
  database: blog_production
  #username: blog
  #password: <%= ENV['BLOG_DATABASE_PASSWORD'] %>

Setup db

$ bin/rails db:setup
$ bin/rails db:migrate

Start server

$ bin/rails server -b 0.0.0.0