Feature or bug? yum module falls back to apt on Debian

[geerlingguy]

SUMMARY

I was working on an example of what not to do—namely, using the yum module instead of package for something meant to be platform agnostic... but then I realized my example (using the yum module on Debian) actually worked.

When I ran the yum task with -vvvv I found:

Running apt as the backend for the yum action plugin
Using module file /usr/local/lib/python2.7/dist-packages/ansible/modules/packaging/os/apt.py

Is this a bug? A feature? I found it can also lead to unexpected weird behavior that I believe is due to strange fallback behavior.

ISSUE TYPE

• Bug Report

COMPONENT NAME

yum

ANSIBLE VERSION

ansible 2.8.5
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/Users/jgeerling/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/local/lib/python2.7/site-packages/ansible
  executable location = /usr/local/bin/ansible
  python version = 2.7.16 (default, Apr 12 2019, 15:32:40) [GCC 4.2.1 Compatible Apple LLVM 10.0.1 (clang-1001.0.46.3)]

CONFIGURATION

N/A

OS / ENVIRONMENT

Debian 10

STEPS TO REPRODUCE

1. Run a Docker image with Debian 10.

   docker run -it geerlingguy/docker-debian10-ansible /bin/bash
   

2. Check if stress installed. Nothing listed.

   apt list --installed | grep stress
   

3. Create a playbook for demonstration.

   cat << EOF > main.yml
   ---
   - hosts: localhost
     gather_facts: false
     connection: local
   
     tasks:
       - apt: update_cache=true
       - yum: name=stress state=present
   EOF
   

4. Run the playbook.

   ansible-playbook main.yml
   

5. Check if stress installed.

   apt list --installed | grep stress
   stress/stable,now 1.0.4-4 amd64 [installed]
   

When run with -vvvv, the yum task gives: https://pastebin.com/Q4SSduVH

EXPECTED RESULTS

I expected a task failure, saying something like "yum or dnf are not available on this system."

ACTUAL RESULTS

The task worked. It said 'changed' or 'ok' and worked idempotently.

I was bewildered. Surprise was apparent. I even said something in IRC about it.

[ansibot]

Files identified in the description:

• lib/ansible/modules/packaging/os/yum.py

If these files are inaccurate, please update the component name section of the description or use the !component bot command.

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[ansibot]

cc @Akasurde @berenddeschouwer @kustodian @maxamillion @verm666
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[geerlingguy]

ansible -m setup output inside the test environment (run where ansible-playbook was run): https://gist.github.com/geerlingguy/be571359470883b83f66b49eb2dbcc0b

[sivel]

We probably need some change like the following to ensure only yum like backends will work:

diff --git a/lib/ansible/plugins/action/yum.py b/lib/ansible/plugins/action/yum.py
index 468321a429..f1efd10bbd 100644
--- a/lib/ansible/plugins/action/yum.py
+++ b/lib/ansible/plugins/action/yum.py
@@ -22,6 +22,8 @@ from ansible.utils.display import Display
 
 display = Display()
 
+VALID_PKG_MGRS = frozenset(("yum", "yum4", "dnf"))
+
 
 class ActionModule(ActionBase):
 
@@ -56,7 +58,7 @@ class ActionModule(ActionBase):
             except Exception:
                 pass  # could not get it from template!
 
-        if module not in ["yum", "yum4", "dnf"]:
+        if module not in VALID_PKG_MGRS:
             facts = self._execute_module(module_name="setup", module_args=dict(filter="ansible_pkg_mgr", gather_subset="!all"), task_vars=task_vars)
             display.debug("Facts %s" % facts)
             module = facts.get("ansible_facts", {}).get("ansible_pkg_mgr", "auto")
@@ -68,7 +70,7 @@ class ActionModule(ActionBase):
             if module == "yum4":
                 module = "dnf"
 
-            if module not in self._shared_loader_obj.module_loader:
+            if module not in self._shared_loader_obj.module_loader or module not in VALID_PKG_MGRS:
                 result.update({'failed': True, 'msg': "Could not find a yum module backend for %s." % module})
             else:
                 # run either the yum (yum3) or dnf (yum4) backend module

[luigizhou]

Hi, I would like to work on this. Has this been fixed already?
Also, this would be my first contribution and I might need some guidance

[maxamillion]

@luigizhou it has not, I would gladly review a patch for it though. I think @sivel's suggestion is a solid starting point. Thank you!