Domain/ELB returning 503 after linking it to wordpress EC2 instance

Question

When I link a domain name to EC2 instance IP, my wordpress setup on the same machine returns 503 error. It runs fine when its not linked to any domain name.

Update: I think I found the reason of error, which would be ELB instance getting 301 as status code, due to redirect (it must be hitting private IP). Still not sure how to fix it though.

Cases:

• If I hit the IP address, it gets redirected to example.com and returns 503 error.
• If I hit example.com, it simply returns 503 error.

I tried a set of changes, but none of them seem to work. The steps were:

1. Add ServerName under /etc/httpd/conf/httpd.conf
2. Add SITE_URL and HOME_URL in wp-config (and the relevant changes in functions.php
3. Update site_url and home_url in wp_options table

But none of these seem to fix it

.htaccess file

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

My original plan was to setup the instance under autoscaling group and load balance it, but even the basic configuration doesn't seem to work. Same thing happens if I link the domain name to ELB url and add the instance under load balancer.