How can I run local-exec provisionner AFTER cloud-init / user_data?

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I'm experiencing a race condition issue on Terraform when running an Ansible playbook with the local-exec provisioner. At one point, that playbook has to install an APT package.

But first, I'm running a cloud-config file init.yml specified in the user_data argument that installs a package as well. Consequently, I'm getting the following error :

Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), is another process using it?

How can I prevent this?

# init.yml

runcmd:
  - sudo apt-get update
  - sudo apt-get -y install python python3

# main.tf

resource "digitalocean_droplet" "hotdog" {
  image     = "ubuntu-18-04-x64"
  name      = "my_droplet"
  region    = "FRA1"
  size      = "s-1vcpu-1gb"
  user_data = file("init.yml")

  provisioner "local-exec" {
    command = "ANSIBLE_HOST_KEY_CHECKING=False ansible-playbook -i '${self.ipv4_address},' ./playbook.yml"
  }
}
terraform ansible
1 Answers

Disclaimer: my terraform knowledge is quite sparse compared to my ansible one. The below should work but there might be terraform centric options I totally missed

A very easy solution is to use an until loop so as to retry the task until it succeeds.

- name: retry apt task every 5s during 1mn until it succeeds (e.g. lock is released)
  apt:
    name: my_package
  register: apt_install
  until: apt_install is success
  delay: 5
  retries: 12

A better approach would be to make sure there is no lock in place on the different dpkg lock files. I did not make the exercise to implement this in ansible and you might need a specific script or custom module to succeed. If you want to give it a try, there is a question with a solution on serverfault

In your context and since this problem seems quite common actually, I searched a bit and I came across this issue on github. I think that my adaptation as below will meet your requirements and might help for any other possible race condition inside your init phase.

Modify your user_data as:

---
runcmd:
  - touch /tmp/user-init-running
  - sudo apt-get update
  - sudo apt-get -y install python python3
  - rm /tmp/user-init-running

And in your playbook:

- name: wait for init phase to end. Error after 1mn
  wait_for:
    path: /tmp/user-init-running
    state: absent
    delay: 60

- name: install package
  apt:
    name: mypkg
    state: present
user_94010960
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