pkg-debian: fix repo idempotence

[jharley]

While doing development with Molecule on 18.04, I discovered that pkg-debian.yml was written in such a way that runs could never be idempotent. This changes the repository file name logic to basically match what is happening in pkg-redhat.yml and makes the role (more?) idempotent.

[KSerrania]

Thanks for the PR! I left a (pretty big) comment discussing how to make the role idempotent while keeping our current guarantees on the role behavior. WDYT?

[KSerrania]

We tried doing that before, but this method has a problem in the following situation:

• Let's say you do a first run with the following configuration:

datadog_agent_major_version: 7
datadog_apt_repo: "deb https://my.custom.repo stable main"

Then, after this run, you have:

$ find /etc/apt/sources.list.d/ -type f -print -exec cat {} \;
/etc/apt/sources.list.d/ansible_datadog_custom.list
deb https://my.custom.repo stable main

• Then, on the following run, you decide to use an official repo and use the following configuration:

datadog_agent_major_version: 7

Because of this, the(Custom) task will be skipped, so the custom repository won't be added, but it won't be removed either, and you'll end up with:

$ find /etc/apt/sources.list.d/ -type f -print -exec cat {} \;
/etc/apt/sources.list.d/ansible_datadog_7.list
deb https://apt.datadoghq.com/ stable 7
/etc/apt/sources.list.d/ansible_datadog_custom.list
deb https://my.custom.repo stable main

and in this situation, the role may have an unexpected behavior as you can't know in advance from which source the installed package will come from.

---

Another problematic situation is the following:

• First run with datadog_apt_repo: "deb https://my.custom.repo stable main"
• Second run with datadog_apt_repo: "deb https://my.custom.repo2 stable main"
  Then you end up with:

$ find /etc/apt/sources.list.d/ -type f -print -exec cat {} \;
/etc/apt/sources.list.d/ansible_datadog_custom.list
deb https://my.custom.repo stable main
deb https://my.custom.repo2 stable main

In this case, you don't know from which custom repository will the package come from.

---

I think the following fix would work for both scenarios while keeping the role idempotency:

• keep your current changes
• remove lines 26-29 (they're useless now)
• add the following tasks before this one:

- name: (Custom) Initialize custom repo file deletion flag to False
  set_fact:
    datadog_remove_custom_repo_file: "False"

- name: (Custom) Check if custom repository file exists
  stat:
    path: /etc/apt/sources.list.d/ansible_datadog_custom.list
  register: datadog_custom_repo_file

- name: (Custom) Flag custom repository file for deletion if different from current repository config
  set_fact:
    datadog_remove_custom_repo_file: "{{ datadog_repo_file_contents != datadog_apt_repo }}"
  vars:
    datadog_repo_file_contents: "{{ lookup('file', '/etc/apt/sources.list.d/ansible_datadog_custom.list') }}"
  when: datadog_custom_repo_file.stat.exists

- name: (Custom) Remove Datadog custom repository file when not set or updated
  file:
    path: /etc/apt/sources.list.d/ansible_datadog_custom.list
    state: absent
  vars:
    repo_file_contents: "{{ lookup('file', '/etc/apt/sources.list.d/ansible_datadog_custom.list') }}"
  when: (not (datadog_apt_repo | length > 0) or datadog_remove_custom_repo_file)  and (not ansible_check_mode)

That way, we make sure the previous custom repository is removed when:

• datadog_apt_repo is not set (that way, we don't keep a previous custom repo activated when we want the official repos)
• datadog_apt_repo has been modified (that way, we only use the custom repository currently specified in the role config).

WDYT?

[jharley]

@KSerrania thanks looking at my PR and for the thoughtful review! I hadn't considered the case that you outlined and agree that your proposed solution seems like the most straightforward way to address things 🚀

[KSerrania]

@jharley I'll cherry-pick the changes you made here and add my own then, if you don't mind.

[jharley]

@KSerrania Not at all! Thank you 🙏

[jharley]

Closing in favour of #262