How do I utilize user data to automatically run a script with every restart of my Amazon EC2 Linux instance?

Short description

By default, user data command and cloud-init directives run only during the first boot cycle when an EC2 instance is launched. However, you can configure your user data command and cloud-init directives with a mime multi-part file.

A mime multi-part file allows your command to override how frequently user data is run in the cloud-init package. Then, the file runs the user command. For more information on mime multi-part files, see Mime multi-part archive on the cloud-init website.

Note: It's a best practice to create a snapshot of your instance before you proceed with the following resolution.

Resolution

Warning: Before you start this procedure, review the following:

• The instance erases data on instance store volumes when you stop and start the instance. Be sure that you back up your data on the instance store volumes. For more information, see AMI types and characteristics in Amazon EC2.
• If your EC2 instance has an auto-assigned public IPv4 address, then a stop and start of the instance causes the IPv4 address to change. To set the instance to have a static public IPv4 address, use an Elastic IP address. Elastic IP addresses persist after an instance stop and start.

Complete the following steps:

1. Make sure that the latest version of cloud-init is installed and functions properly on your EC2 instance.
2. Make sure that the IAM user or role you use has the ec2:ModifyInstanceAtrribute permission listed in its IAM policy. For more information, see Editing IAM policies.
3. Open the Amazon EC2 console.
4. Stop your instance.
5. Choose Actions, choose Instance Settings, and then choose Edit User Data.
6. Copy your user command into the Edit user data box, and then choose Save.
   The following example is a shell command that writes "Hello World" to a testfile.txt file in a /tmp directory.

   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" >> /tmp/testfile.txt
   --//--

   By default, cloud-init allows only one content type in user data at a time. However, this example shows both text/cloud-config and text/x-shellscript content-types in a mime-multi part file.
   Set the scripts-user parameter to always so the text/cloud-config content type overrides how frequently user data is run in the cloud-init package.
   The text/x-shellscript content type provides the user command to run the cloud-init cloud_final_modules module.
   Note: Replace the line /bin/echo "Hello World." >> /tmp/testfile.txt with your shell command that you want to run during the instance boot.
7. Start your EC2 instance again, and then validate that your script runs correctly.
   Note: If your script did not run as expected, then check the /var/log/cloud-init-output.log file. For more information, see How to debug cloud-init on the cloud-init website.

Related information

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User data formats on the cloud-init website