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Automatically run bash script with every restart of AWS EC2 instance

We will be using User Data script to define our autorun script, which we intend to execute on every reboot or launch of our EC2 instance. I will be using this script to mount my elastic file system drive (EFS) and start to do application server configuration every time my server is rebooted and auto-scale using my autoscaling configuration.

To start here's little into of user data script. By default, user data scripts and cloud-init directives run only during the first boot cycle when an EC2 instance is launched. However, you can configure your user data script and cloud-init directives with a mime multi-part file. A mime multi-part file allows your script to override how frequently user data is executed in the cloud-init package. Then, the file executes the user script. For more information on mime multi-part files, see Mime Multi Part Archive on the cloud-init website.

Example of User Data script: 

Content-Type: multipart/mixed; boundary="//"
MIME-Version: 1.0

--//
Content-Type: text/cloud-config; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="cloud-config.txt"

#cloud-config
cloud_final_modules:
- [scripts-user, always]

--//
Content-Type: text/x-shellscript; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="userdata.txt"

!/bin/bash
/bin/echo "Hello World" >> /home/ec2-user/logscript.txt
yum update -y
/bin/echo "Hello World -2" >> /home/ec2-user/logscript.txt
mkdir /home/ec2-user/efs
/bin/mount -t nfs4 -o nfsvers=4.1,rsize=1048576,wsize=1048576,hard,timeo=600,retrans=2,noresvport 172.31.XX.XXX:/ /home/ec2-user/efs
/bin/echo "file server mounting completed, ready to start the server..." >> /home/ec2-user/logscript.txt
/home/ec2-user/efs/Tomcat/bin/startup.sh
/bin/echo "tomcat server started" >> /home/ec2-user/logscript.txt
--//

** important notes:- here I have created a file called 'logscript.txt' on my ec2 instance, to log all output of the script. As you can see, I am defining my bash script in this user data script (in Red). You can replace the Red text with your custom script. 
Add caption

Defining User Data on EC2:
  1. Go to your EC2 panel
  2. Select the instance, Go to Action --> Instance Settings --> View/Change User Data
  3. You can modify User data only when your instance is in the "Stop" state. Before stopping make use follow the process as stop may change your public IP address.
  4. Put the following script, click Save
  5. Go to Instance State and 'Start'  



You can verify the logscript.txt to check if your script executed or not. 

Happy deploying!

--
Deepesh Rajpal | c: 98282.38079 | rajpal.deepesh@gmail.com

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