How to fire EC2 instances and upload/run a startup script on each of them?

The answer depends a bit on what AMI you are running as the features provided are entirely AMI dependent.

The Amazon Linux AMIS and the official Ubuntu AMIs have the cloud-init package installed. This has a number of ways you can trigger startup actions, but the one that matches your request most closely (and my favorite because I invented it) is the concept of a user-data script.

You can simply pass any script (starting with the two characters #!) as the user-data when starting the EC2 instances. It will be run as root on the first boot of the instance.

For a specific example of how this works, I use this exact technique in my recent article: Uploading Known ssh Host Key in EC2 user-data Script

You also wanted to run more than one EC2 instance with the same script. The ec2-run-instances command and the related APIs and web console allow you to specify any number of instances to start with the same user-data. For example:

ec2-run-instances            \
  --instance-count 10        \
  --user-data-file $MYSCRIPT \
  --key $USER                \
  $SOMEAMI

If you are currently running an AMI that does not have cloud-init installed, you could do one of:

• Switch to an AMI that has cloud-init installed, or

• Build a custom version of your AMI that has cloud-init installed, or

• Write a more complicated wrapper script that makes a record of all of the instance ids after they are kicked off, waits for all of the instances to move to the running state, waits for the sshd to accept connections, uploads your startup script to each instance, and runs the startup script on each instance.

I have a tutorial to run the script in the "cloud-init" that runs each time AWS EC2 is startup.

• to set configuration file (AWS CentOS6) and

• run the scripts when you startup the EC2

To set configuration file on Linux you may refer configure cloud-init on AWS Linux.

I personally use AWS VPC/EBS that was setup based on Linux AMI, I didn't touch anything on the configuration file /etc/cloud/cloud.cfg but my boot script in the cloud-init runs well.