install posgresql 9.4

mkdir install_pg
cd install_pg
wget  https://yum.postgresql.org/9.4/redhat/rhel-7-x86_64/pgdg-centos94-9.4-3.noarch.rpm
sudo yum -y install http://yum.postgresql.org/9.4/redhat/rhel-7-x86_64/pgdg-centos94-9.4-3.noarch.rpm
sudo yum -y groupinstall "PostgreSQL Database Server 9.4 PGDG"

check if everything was correctly installed

sudo rpm -qa | grep postgre
postgresql94-server-9.4.16-1PGDG.rhel7.x86_64
postgresql94-libs-9.4.16-1PGDG.rhel7.x86_64
postgresql94-9.4.16-1PGDG.rhel7.x86_64
postgresql94-contrib-9.4.16-1PGDG.rhel7.x86_64

enable & start service

sudo systemctl enable postgresql-9.4
sudo systemctl start postgresql-9.4.service

initialize database

sudo /usr/pgsql-9.4/bin/postgresql94-setup initdb

firewall adjustment (open ports)

firewall-cmd --permanent --add-port=5432/tcp
firewall-cmd --permanent --add-port=80/tcp
firewall-cmd --reload

enable SELinux

setsebool -P httpd_can_network_connect_db 1

change password for the

sudo passwd postgres (user prompted twice for a password)

edit the posgresql configuration file

vim /var/lib/pgsql/9.4/data/pg_hba.conf
Change from:
host    all             all             127.0.0.1/32            ident
# IPv6 local connections:
host    all             all             ::1/128                 ident

To:
host    all             all             127.0.0.1/32            md5
# IPv6 local connections:
host    all             all             ::1/128                 md5

posgresql 9.4 binaries (should set postgresql ENV!)

all postgresql 9.4 binaries are installed at /usr/pgsql-9.4/bin

Change password for the 'postgres' user

sudo passwd postgres

If root/sudo rights are unavailable use sudo:
sudo -i -u postgres
at the prompt then enter:
passwd to change the user password

Decko installation

create a db user (asks for the password twice) will have to be written at the config/database.yml

# -d (--createdb) (role can create new databases)
# -P (--pwprompt) (assign a password to new role)
createuser -d <db_user> -P (CREATE ROLE alias)

create database which will have to be written at the config/database.yml

# probably not needed decko seed will create the database
# create database via user
# -O (--owner=OWner) (database user to own the new database)
# createdb -O <db_user> <database>

Edit Gemfile and add the pg gem

gem 'pg', '~> 0.18'

edit config/database.yml

# Add this after the cucumber: *test line

production: &production
  adapter: postgresql
  encoding: utf8
  reconnect: false
  database: <database_name>
  pool: 5
  username: <db_user>
  password: <db_user_password>
  host: localhost

I'm fuzzy here on the profile (probably if you want to change to production then change it?)
@ethn could you please fill it here?
profile: *production

What is the correct format for production deployment?

Now to install all gems and seed the application

install decko gem

gem install decko

install new application

decko new _app_name_

change directory

cd _app_name_

install all needed gems (this is probably optional but I'm used to doing it manually)

bundle install

prefill the DB and have the original configuration

decko seed

If everything went fine you should see:

bundle exec rake decko:seed
--> Database '<db_name>' already exists  (This is extra as I had the database already)
not dropped
creating
loading schema
-- create_table("card_actions", {:id=>:integer, :force=>:cascade})
   -> 0.0542s
-- create_table("card_acts", {:id=>:integer, :force=>:cascade})
   -> 0.0250s
-- create_table("card_changes", {:id=>:integer, :force=>:cascade})
   -> 0.0121s
-- create_table("card_references", {:id=>:integer, :force=>:cascade})
   -> 0.0290s
-- create_table("card_revisions", {:id=>:integer, :force=>:cascade})
   -> 0.0157s
-- create_table("cards", {:id=>:integer, :force=>:cascade})
   -> 0.0571s
-- create_table("delayed_jobs", {:force=>:cascade})
   -> 0.0146s
-- create_table("schema_migrations_core_cards", {:id=>false, :force=>:cascade})
   -> 0.0095s
-- create_table("schema_migrations_deck_cards", {:id=>false, :force=>:cascade})
   -> 0.0084s
-- create_table("sessions", {:id=>:integer, :force=>:cascade})
   -> 0.0107s
-- create_table("users", {:id=>:integer, :force=>:cascade})
   -> 0.0073s
update card_migrations
-- assume_migrated_upto_version("20170830210517", ["/home/smalltalk/.rvm/gems/ruby-2.3.0/gems/card-1.93.8/db/migrate_core_cards"])
   -> 0.0321s
loading bootstrap
set symlink for assets
reset cache

Then you can start the built-in WEBrick server as mentioned at the https://github.com/decko-commons/decko/blob/master/decko/README.rdoc

You should see (when started correctly):

decko server
=> Booting Thin
=> Rails 5.1.4 application starting in production on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
Thin web server (v1.7.2 codename Bachmanity)
Maximum connections set to 1024
Listening on 0.0.0.0:3000, CTRL+C to stop