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How to edit and re-run Cloud-Config user data?

Posted July 25, 2019 10.6k views
Initial Server SetupUbuntu 18.04

I’m debugging a Cloud-Config user data script. It’d be nice to make changes and re-run, without rebooting, if that’s possible?

Here’s me doing it wrong:

#cloud-config

runcmd:
  - date >> /var/log/runcmd.log

After the instance boots, /var/log/cloud-init.log has:

Running module runcmd
[...]
finish: modules-config/config-runcmd: SUCCESS: config-runcmd ran successfully

and runcmd.log has one entry – so far, so good. Goal #1 is to add a second entry.

cloud-init init seems to only run vendor data. The internet says to first run cloud-init clean. This seems to delete my user data.

cloud-init single --name runcmd --frequency always writes the script out, but never runs it:

Cloud-init v. 19.1-1-gbaa47854-0ubuntu1~18.04.1 running 'single'
[...]
Writing to /var/lib/cloud/instances/152272562/scripts/runcmd - wb: [700] 38 bytes
Reading from /proc/uptime (quiet=False)
Read 14 bytes from /proc/uptime
cloud-init mode 'single' took 0.198 seconds (0.20)

I beleive the semaphore file is ignored ignored with --frequency always. Removing the semaphore file didn’t help.

If I reach goal #1, the second is to edit the user data – will Cloud-Config read from /var/lib/cloud/instance/user-data.txt, or is this just an artifact?

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2 answers
AHA July 25, 2019

I’ve run into that same cloud-init debugging issue myself, I’m asking around internally to see if anyone has a way to re-run the cloud-init user data in a running vm.

One alternative: If you install doctl you can create droplets from the CLI and specify a local file as user-data.

There’s probably a way to automate it further, but I’ve found myself running:

doctl compute droplet create <name> --user-data-file <path-to-file> --region <region-slug> --image <image-slug> --size <size-slug> --ssh-keys <saved-key-id>

This isn’t perfect, but it at least allows you to make edits to your cloud-init and quickly deploy a new instance to test.

Even kicking off 5 creates of 1GB instances will only cost you $0.007x5 = 3.5 cents, as long as you remember to delete!

EDIT: Also to answer your last q: I’m pretty sure /var/lib/cloud/instance/user-data.txt, IS just an artifact. I.E. if you edit it and rebuild the Droplet it will still run your original user-data

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blackpotoftea April 30, 2020

To run “runcmd” you have to execute two modules:

  1. runcmd create script
  2. scripts_user actually runs it
 cloud-init --file cloud-init.yaml single --name runcmd --frequency=always
 cloud-init --file cloud-init.yaml single --name scripts_user --frequency=always
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