AWS Solutions for the issues of accessing yum

https://forums.aws.amazon.com/thread.jspa?messageID=623084
http://stackoverflow.com/questions/20822021/amazon-ec2-instance-cant-update-or-use-yum

Solution 1.
VPC
DNS resolution: no
DNS hostnames: no
→
DNS resolution: yes
DNS hostnames: yes

Solution 2.
Route Table
0.0.0.0/0: Internet Gateway

Solution 3.
Elastic IP
Associate an Elastic IP address with the instance temporarily.