Use yum priorities for RDO

This patch installs the yum priorities plugin and ensures that RDO
has a higher priority than EPEL. This ensures that the packages from
the RDO repository are preferred over those from EPEL.

Related-bug: 1670012
Change-Id: Ib31e8379f98c91707e9e09207b873f3f597679e6

tasks/pre_install_apt.yml

@@ -19,7 +19,7 @@
     cache_valid_time: "{{ cache_timeout }}"
 
 # Under Ubuntu, this will only add the key
-- name: Install external repo key with package
+- name: Install UCA repository key
   apt:
     name: "{{ pip_install_external_repo_key_package }}"
     state: "{{ pip_install_external_repo_key_package_state | default('present') }}"
@@ -28,7 +28,7 @@
   tags:
     - add-repo-keys
 
-- name: Install repo for distro binaries
+- name: Install UCA repository
   apt_repository:
     repo: "{{ uca_repo }}"
     state: present

tasks/pre_install_yum.yml

@@ -14,7 +14,7 @@
 # limitations under the License.
 
 # Under CentOS, this will add the repo and its key to the keyring
-- name: Install external repo key with package
+- name: Install RDO repository and key
   yum:
     name: "{{ pip_install_external_repo_key_package }}"
     state: "{{ pip_install_external_repo_key_package_state | default('present') }}"
@@ -23,6 +23,24 @@
   tags:
     - add-repo-keys
 
+# NOTE: All yum repositories are priority 99 (lowest possible) by default.
+#       EPEL and RDO have packages that conflict (especially with RabbitMQ's
+#       Erlang dependencies). This task ensures that RDO is always preferred
+#       over EPEL when both are configured.
+# TODO(mhayden): If the yum_repository module is improved to allow for edits to
+#                existing repository files, this task should be updated to use
+#                yum_repository instead of ini_file.
+#                Ansible bug: https://github.com/ansible/ansible/issues/22362
+- name: Increase priority for RDO repository
+  ini_file:
+    dest: "{{ item.path }}"
+    section: "{{ item.section }}"
+    option: priority
+    value: 50
+  with_items:
+    - { path: "/etc/yum.repos.d/rdo-release.repo", section: "openstack-ocata" }
+    - { path: "/etc/yum.repos.d/rdo-qemu-ev.repo", section: "rdo-qemu-ev"}
+
 - name: Install external repo key manually
   rpm_key:
     key: "{{ item.key }}"

vars/redhat-7.yml

@@ -22,6 +22,7 @@ pip_install_distro_build_packages:
   - python-devel
   - python-pyasn1
   - python2-pyOpenSSL
+  - yum-plugin-priorities
 
 pip_required_pip_packages:
   - ndg-httpsclient # SSL SNI support