Merge "Support nodes setting 'auto' python-path"

README.rst

@@ -64,9 +64,8 @@ at the tops of individual source files.
 Python Version Support
 ----------------------
 
-Zuul v3 requires Python 3. It does not support Python 2.
+Zuul requires Python 3. It does not support Python 2.
+
+Since Zuul uses Ansible to drive CI jobs, Zuul can run tests anywhere
+Ansible can, including Python 2 environments.
 
-As Ansible is used for the execution of jobs, it's important to note that
-while Ansible does support Python 3, not all of Ansible's modules do. Zuul
-currently sets ``ansible_python_interpreter`` to python2 so that remote
-content will be executed with Python 2.

doc/source/admin/components.rst

@@ -797,6 +797,42 @@ To enable or disable running Ansible in verbose mode (with the
 ``-vvv`` argument to ansible-playbook) run ``zuul-executor verbose``
 and ``zuul-executor unverbose``.
 
+Ansible and Python 3
+~~~~~~~~~~~~~~~~~~~~
+
+As noted above, the executor runs Ansible playbooks against the remote
+node(s) allocated for the job.  Since part of executing playbooks on
+remote hosts is running Python scripts on them, Ansible needs to know
+what Python interpreter to use on the remote host.  With older
+distributions, ``/usr/bin/python2`` was a generally sensible choice.
+However, over time a heterogeneous Python ecosystem has evolved where
+older distributions may only provide Python 2, most provide a mixed
+2/3 environment and newer distributions may only provide Python 3 (and
+then others like RHEL8 may even have separate "system" Python versions
+to add to confusion!).
+
+Ansible's ``ansible_python_interpreter`` variable configures the path
+to the remote Python interpreter to use during playbook execution.
+This value is set by Zuul from the ``python-path`` specified for the
+node by Nodepool; see the `nodepool configuration documentation
+<https://zuul-ci.org/docs/nodepool/configuration.html>`__.
+
+This defaults to ``auto``, where Ansible will automatically discover
+the interpreter available on the remote host.  However, this setting
+only became available in Ansible >=2.8, so Zuul will translate
+``auto`` into the old default of ``/usr/bin/python2`` when configured
+to use older Ansible versions.
+
+Thus for modern Python 3-only hosts no further configuration is needed
+when using Ansible >=2.8 (e.g. Fedora, Bionic onwards).  If using
+earlier Ansible versions you may need to explicitly set the
+``python-path`` if ``/usr/bin/python2`` is not available on the node.
+
+Ansible roles/modules which include Python code are generally Python 3
+safe now, but there is still a small possibility of incompatibility.
+See also the Ansible `Python 3 support page
+<https://docs.ansible.com/ansible/latest/reference_appendices/python_3_support.html>`__.
+
 .. _web-server:
 
 Web Server

releasenotes/notes/ansible-interp-auto-4b4ecb4678c11470.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    Nodes can set their ``python-path`` in nodepool configuration to
+    ``auto`` to allow for `automatic ansible_python_interpreter
+    discovery <https://docs.ansible.com/ansible/2.8/reference_appendices/interpreter_discovery.html>`__
+    when using Ansible >=2.8.

tests/base.py

@@ -2507,7 +2507,7 @@ class FakeNodepool(object):
         self.remote_ansible = False
         self.attributes = None
         self.resources = None
-        self.python_path = '/usr/bin/python2'
+        self.python_path = 'auto'
 
     def stop(self):
         self._running = False

tests/fixtures/config/inventory/git/common-config/playbooks/ansible-version.yaml

@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []

tests/fixtures/config/inventory/git/common-config/zuul.yaml

@@ -89,4 +89,20 @@
           label: ubuntu-xenial
     run: playbooks/jinja2-message.yaml
 
+- job:
+    name: ansible-version27-inventory
+    nodeset:
+      nodes:
+        - name: ubuntu-xenial
+          label: ubuntu-xenial
+    ansible-version: '2.7'
+    run: playbooks/ansible-version.yaml
 
+- job:
+    name: ansible-version28-inventory
+    nodeset:
+      nodes:
+        - name: ubuntu-xenial
+          label: ubuntu-xenial
+    ansible-version: '2.8'
+    run: playbooks/ansible-version.yaml

tests/fixtures/config/inventory/git/org_project/.zuul.yaml

@@ -7,3 +7,5 @@
         - executor-only-inventory
         - group-inventory
         - hostvars-inventory
+        - ansible-version27-inventory
+        - ansible-version28-inventory

tests/unit/test_inventory.py

@@ -76,6 +76,57 @@ class TestInventoryPythonPath(TestInventoryBase):
         self.waitUntilSettled()
 
 
+class TestInventoryAutoPython(TestInventoryBase):
+
+    def test_auto_python_ansible28_inventory(self):
+        inventory = self._get_build_inventory('ansible-version28-inventory')
+
+        all_nodes = ('ubuntu-xenial',)
+        self.assertIn('all', inventory)
+        self.assertIn('hosts', inventory['all'])
+        self.assertIn('vars', inventory['all'])
+        for node_name in all_nodes:
+            self.assertIn(node_name, inventory['all']['hosts'])
+            node_vars = inventory['all']['hosts'][node_name]
+            self.assertEqual(
+                'auto', node_vars['ansible_python_interpreter'])
+
+        self.assertIn('zuul', inventory['all']['vars'])
+        z_vars = inventory['all']['vars']['zuul']
+        self.assertIn('executor', z_vars)
+        self.assertIn('src_root', z_vars['executor'])
+        self.assertIn('job', z_vars)
+        self.assertEqual(z_vars['job'], 'ansible-version28-inventory')
+        self.assertEqual(z_vars['message'], 'QQ==')
+
+        self.executor_server.release()
+        self.waitUntilSettled()
+
+    def test_auto_python_ansible27_inventory(self):
+        inventory = self._get_build_inventory('ansible-version27-inventory')
+
+        all_nodes = ('ubuntu-xenial',)
+        self.assertIn('all', inventory)
+        self.assertIn('hosts', inventory['all'])
+        self.assertIn('vars', inventory['all'])
+        for node_name in all_nodes:
+            self.assertIn(node_name, inventory['all']['hosts'])
+            node_vars = inventory['all']['hosts'][node_name]
+            self.assertEqual(
+                '/usr/bin/python2', node_vars['ansible_python_interpreter'])
+
+        self.assertIn('zuul', inventory['all']['vars'])
+        z_vars = inventory['all']['vars']['zuul']
+        self.assertIn('executor', z_vars)
+        self.assertIn('src_root', z_vars['executor'])
+        self.assertIn('job', z_vars)
+        self.assertEqual(z_vars['job'], 'ansible-version27-inventory')
+        self.assertEqual(z_vars['message'], 'QQ==')
+
+        self.executor_server.release()
+        self.waitUntilSettled()
+
+
 class TestInventory(TestInventoryBase):
 
     def test_single_inventory(self):

zuul/executor/server.py

@@ -1370,9 +1370,23 @@ class AnsibleJob(object):
                         private_ipv4=node.get('private_ipv4'),
                         public_ipv6=node.get('public_ipv6'))))
 
-                host_vars.setdefault(
-                    'ansible_python_interpreter',
-                    node.get('python_path', '/usr/bin/python2'))
+                # Ansible >=2.8 introduced "auto" as an
+                # ansible_python_interpreter argument that looks up
+                # which python to use on the remote host in an inbuilt
+                # table and essentially "does the right thing"
+                # (i.e. chooses python3 on 3-only hosts like later
+                # Fedoras).  For "auto" with prior versions, fall back
+                # to the old default of /usr/bin/python2 for backwards
+                # compatability.
+                python = node.get('python_path', 'auto')
+                compat = self.arguments.get('ansible_version') in \
+                    ('2.5', '2.6', '2.7')
+                if python == "auto" and compat:
+                    self.log.debug(
+                        "ansible_version set to auto but "
+                        "overriding to python2 for Ansible <2.8")
+                    python = '/usr/bin/python2'
+                host_vars.setdefault('ansible_python_interpreter', python)
 
                 username = node.get('username')
                 if username: