UPDATE --July-2018
Original instruction was installing postgresql-server-9.2. Atlassian has dropped support for v9.2 for newer versions. The post updated to install Postgresql-server v9.6 instead. 
If you have followed original post, and now want to update your database server to the latest, you can follow this post: How to upgrade Postgresql server to v9.6

Update 2018-03-06: I created a script that will do all the steps described on this page and the second part on this page in one place in much easier way. You can download it from github.

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Up until now I always have used Mysql server for Confluence instances. PostgreSQL is Atlassian preferred database for Confluence and their other products. So I will go through installation steps for this configuration. I already have a fresh minimal Centos 7 installation.

Atlassian has a guide for this but it is generic covering all possible combinations and for this specific installation one need to jump between various pages. This post will have all you need to know on how to install Atlassian Confluence on Centos 7 in one place.

After you completed steps in this post, you can continue to make your connections secure and encrypted by following the steps on this page. http://comtronic.com.au/how-to-enable-ssl-on-confluence-centos-7/

All the details and screenshots are correct for below set-up:

OS: Centos 7.5  ( Linux 3.10.0-327.36.3.el7.x86_64)
Confluence Server:  atlassian-confluence-6.10.1-x64
Database Server: PostgreSQL-9.6.9

Preparation

Before start, you need to decide where to download your resources. I usually have my resources in one place. Create a folder for it if you haven’t got one.

sudo yum update
sudo yum install vim wget

Install database server

Atlassian’s recommended database engine for Jira is PostgreSQL. It is also easiest option to install because it doesn’t need extra steps to download Java connector separately.

The version  that Centos7 repository includes at the moment is v9.2. It not supported by Atlassian products any more. So will need to use community repository the get the latest version of v9.6.

sudo yum install https://download.postgresql.org/pub/repos/yum/9.6/redhat/rhel-7-x86_64/pgdg-centos96-9.6-3.noarch.rpm
sudo yum install postgresql96-server

After installing the packages, you need to initialise and configure it.

Initialise

sudo /usr/pgsql-9.6/bin/postgresql96-setup initdb

Initializing database ... OK

Control service

sudo systemctl enable postgresql-9.6
sudo systemctl start postgresql-9.6

create and set-up database

sudo -u postgres -i
-bash-4.2$ psql
psql (9.6.9)
Type "help" for help.

postgres=# CREATE USER confluencedbuser PASSWORD 'confluencedbpassword';
postgres=# CREATE DATABASE confluencedb WITH ENCODING 'UNICODE' LC_COLLATE 'C' LC_CTYPE 'C' TEMPLATE template0;
postgres=# GRANT ALL PRIVILEGES ON DATABASE confluencedb to confluencedbuser;
\q
-bash-4.2$ exit

configure authentication methods

default authentication method for local connections in PostgreSQL is set to ‘ident’ that means it will get the operating system user name of the client by contacting the ident server on the client and check if it matches the requested database user name. You can read more on this on official PostgreSQL site.

As we are not planing to have a ident server this needs to be updated. I use md5 method. You can consider other methods too depending on the situation. All these settings resting in pg_hba.conf file in data folder of the postgresql installation.

so need to do below:

sudo -u postgres -i 
-bash-4.2$ vim /var/lib/pgsql/9.6/data/pg_hba.conf

Update the line beginning with host. It is towards the end of the file (line 82 in my case) the one starts with host.

this line:

host    all             all             127.0.0.1/32            ident

change it to:

host    all             all             127.0.0.1/32            md5

Open firewall ports

Centos 7 now comes with firewalld pre-installed and activated in some templates by default. You need to open the needed ports to get access to the server through web browser.

First check the active zones:

firewall-cmd --get-active-zones
public
  interfaces: eth0

then you can add the ports needed to the zones you want (public here)

sudo firewall-cmd --zone=public --add-port=8090/tcp --permanent

If you want to redirect the traffic to port 80 for the ease of access follow the next commands, otherwise you can skip them.

It is not recommended for production servers that are open to public. For production servers you can follow my other post to serve on https here. How to enable ssl for Jira Software on Centos7

sudo firewall-cmd --zone=public --add-masquerade --permanent
sudo firewall-cmd --zone=public --add-forward-port=port=80:proto=tcp:toport=8090 --permanent
sudo firewall-cmd --zone=public --add-port=80/tcp --permanent

Remember to reload the firewall for changes to take effect.

sudo firewall-cmd --reload

Now if you have the correct DNS server set-up, to get to the Jira home page you just need to point to the server host name (http://localjiraserver) and not http://localjiraserver:8090.

Download and Install Confluence

sudo mkdir /opt/atlassian
cd /opt/atlassian/
sudo wget https://downloads.atlassian.com/software/confluence/downloads/atlassian-confluence-6.10.1-x64.bin
sudo chmod +x atlassian-confluence-6.10.1-x64.bin

Install

sudo ./atlassian-confluence-6.10.1-x64.bin

Unpacking JRE ...
Starting Installer ...
Nov 05, 2016 10:54:28 PM java.util.prefs.FileSystemPreferences$2 run
INFO: Created system preferences directory in java.home.

This will install Confluence 6.10.1 on your computer.

OK [o, Enter], Cancel [c]
o
Click Next to continue, or Cancel to exit Setup.

Choose the appropriate installation or upgrade option.
Please choose one of the following:
Express Install (uses default settings) [1],
Custom Install (recommended for advanced users) [2, Enter],
Upgrade an existing Confluence installation [3]
2

Select the folder where you would like Confluence 6.10.1 to be installed,
then click Next.

Where should Confluence 6.10.1 be installed?
[/opt/atlassian/confluence]

Default location for Confluence data
[/var/atlassian/application-data/confluence]

Configure which ports Confluence will use.
Confluence requires two TCP ports that are not being used by any other
applications on this machine. The HTTP port is where you will access
Confluence through your browser. The Control port is used to Startup and
Shutdown Confluence.

Use default ports (HTTP: 8090, Control: 8000) - Recommended [1, Enter], Set custom value for HTTP and Control ports [2]
1

Confluence can be run in the background.
You may choose to run Confluence as a service, which means it will start
automatically whenever the computer restarts.
Install Confluence as Service?
Yes [y, Enter], No [n]
y.

Extracting files ...


Please wait a few moments while we configure Confluence.

Installation of Confluence 6.10.1 is complete
Start Confluence now?
Yes [y, Enter], No [n]
y

Please wait a few moments while Confluence starts up.
Launching Confluence ...
Installation of Confluence 6.10.1 is complete
Your installation of Confluence 6.10.1 is now ready and can be accessed via your browser.

Confluence 6.10.1 can be accessed at http://localhost:8090

Confluence 6.10.1 may take several minutes to load on first start up.
Finishing installation ...

Now all is set to start setting up your server.

Set up Confluence

Open your

web browser and point to the address that you installed the server.

Select the language and PostgreSQL as external database.