Fix distribution detection on Amazon Linux 2023 (#612)

* add a test to ensure we don't detect amazonlinux as RHEL6

* disable RHEL 6 detection on amazon linux

All the supported version have a recent enough glibc, so we can install
the most recent agents there.
Our RHEL version checking isn't compatible with Amazon linux 2023 which
causes us to prevent installing any version above 7.51 there.

* pin a specific python version for old ansible versions

* don't attempt to use python2 on AL2023

* add debug

* ensure AL2023 will use dnf instead of yum

.circleci/config.yml

@@ -356,6 +356,24 @@ jobs:
       - run: >
           ansible-playbook -v -i ./ci_test/inventory/ci.ini "./ci_test/install_installer_over_pinned.yaml"
 
+  test_incorrect_rhel6_detect:
+    # Ensure some RHEL derivatives aren't incorrectly detected as RHEL 6
+    docker:
+      - image: datadog/docker-library:ansible_<<parameters.os>>_<<parameters.ansible_version>>
+    parameters:
+      jinja2_native:
+        type: string
+        default: "false"
+      os:
+        type: string
+      ansible_version:
+        type: string
+      python:
+        type: string
+    steps:
+      - checkout
+      - run: ANSIBLE_JINJA2_NATIVE="<<parameters.jinja2_native>>" ansible-playbook -i ./ci_test/inventory/ci.ini ./ci_test/install_agent_7_pinned.yaml -e 'ansible_python_interpreter=/usr/bin/<<parameters.python>>'
+      - run: datadog-agent version
 
 workflows:
   version: 2
@@ -472,3 +490,9 @@ workflows:
 
       - test_installer_over_pinned
 
+      - test_incorrect_rhel6_detect:
+         matrix:
+           parameters:
+              ansible_version: ["4_10"]
+              os: [ "amazonlinux2023"]
+              python: ["python3"]

ci_test/install_agent_7_pinned.yaml

@@ -0,0 +1,13 @@
+---
+
+- hosts: all
+  roles:
+    - { role: '/root/project/'}
+  vars:
+    datadog_api_key: "11111111111111111111111111111111"
+    datadog_enabled: false
+    # Target a version above 7.51 which is the last version supported on RHEL6 and similar
+    # This is to ensure we don't incorrectly detect some configurations as RHEL6
+    datadog_agent_version: '7.53.0'
+    # avoid checking that the agent is stopped for centos
+    datadog_skip_running_check: true

tasks/pkg-redhat.yml

@@ -1,6 +1,6 @@
 ---
 - name: Check for Centos < 7 and adjust features
-  when: ansible_facts.os_family == "RedHat"
+  when: ansible_facts.os_family == "RedHat" and ansible_distribution != "Amazon"
   block:
     - name: Get RHEL major version equivalent
       command: "rpm -E %{rhel}"  # noqa: command-instead-of-module
@@ -21,6 +21,13 @@
     msg: "Agent versions {{ agent_datadog_major }}.{{ datadog_agent_max_minor_version + 1 }} and above not supported by current OS (RHEL < 7 equivalent)."
   when: datadog_agent_max_minor_version is defined and agent_datadog_minor is defined and agent_datadog_minor | int > datadog_agent_max_minor_version
 
+  # Some ansible versions appear to detect yum as the wanted package manager on AL2023.
+  # This can't work since AL2023 only ships python3 and the yum module needs python2
+- name: Ensure dnf is used on Amazon Linux 2023
+  set_fact:
+    ansible_pkg_mgr: dnf
+  when: ansible_facts.distribution == "Amazon" and ansible_facts.distribution_major_version | int >= 2023 and ansible_pkg_mgr == "yum"
+
 - name: Fail early if Python 3 is used on CentOS / RHEL < 8 with old Ansible
   fail:
     msg: "The installation of the Agent on RedHat family systems using yum is not compatible with Python 3 with older Ansible versions.