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

Last updated: 2021-02-10

I want to utilize user data to run a script every time my Amazon Elastic Compute Cloud (Amazon EC2) instance is restarted. How can I do that?

Short description

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 run in the cloud-init package. Then, the file runs the user script. For more information on mime multi-part files, see Mime Multi Part Archive on the cloud-init website.


Warning: Before starting this procedure, review the following:

1.    Make sure that the latest version of cloud-init is installed and functioning properly on your EC2 instance.

2.    For security reasons, create an IAM policy to restrict the users who are allowed to add or remove user data through the ModifyInstanceAttribute API.

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 script into the Edit user data box, and then choose Save.

The following example is a shell script 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"

- [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/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.

The text/cloud-config content type overrides how frequently user data is run in the cloud-init package by setting the SCRIPTS-USER parameter to ALWAYS.

The text/x-shellscript content type provides the actual user script to be run by the cloud-init cloud_final_modules module. In this example, there is only one line to be run, which is /bin/echo "Hello World." >> /tmp/testfile.txt.

Note: Replace the line /bin/echo "Hello World." >> /tmp/testfile.txt with the shell script that you want to run during the instance boot.

7.    Start your EC2 instance again, and validate that your script runs correctly.