Adds nova-compute drain role

roles/nova_compute_drain/defaults/main.yml

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+---
+
+nova_compute_drain_venv: "{{ virtualenv_path }}/openstack"
+nova_compute_drain_delegate_host: "{{ groups['controllers'][0] }}"

roles/nova_compute_drain/tasks/cold-migrate.yml

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+---
+
+- block:
+  - name: "Cold migrate instance: {{ instance_uuid }}"  # noqa no-changed-when
+    command: >
+      {{ nova_compute_drain_venv }}/bin/openstack
+      --os-compute-api-version 2.25
+      server migrate
+      {{ instance_uuid }}
+      --wait
+    register: result
+
+  - name: "Wait for VERIFY_RESIZE: {{ instance_uuid }}"
+    command: >
+      {{ nova_compute_drain_venv }}/bin/openstack server show {{ instance_uuid }} -f value -c status
+    register: result
+    until: result.stdout == 'VERIFY_RESIZE' or result.stdout == 'SHUTOFF'
+    changed_when: false
+    retries: 10
+    delay: 30
+
+  - name: "Confirm resize: {{ instance_uuid }}"  # noqa no-changed-when
+    command: >
+      {{ nova_compute_drain_venv }}/bin/openstack server migrate confirm {{ instance_uuid }}
+    when: result.stdout == 'VERIFY_RESIZE'
+
+  - name: "Wait for SHUTOFF: {{ instance_uuid }}"
+    command: >
+      {{ nova_compute_drain_venv }}/bin/openstack server show {{ instance_uuid }} -f value -c status
+    register: result
+    until: result.stdout == 'SHUTOFF'
+    retries: 10
+    delay: 30
+    changed_when: false
+  environment: "{{ openstack_auth_env }}"
+  delegate_to: "{{ nova_compute_drain_delegate_host }}"
+  vars:
+    ansible_host: "{{ hostvars[nova_compute_drain_delegate_host].ansible_host }}"
+  rescue:
+    - meta: noop # noqa unnamed-task

roles/nova_compute_drain/tasks/instance-info.yml

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+---
+- name: Query instances
+  command: >
+    {{ nova_compute_drain_venv }}/bin/openstack
+    server list --host {{ ansible_facts.nodename }}
+    --all-projects
+    --format json
+  register: instances
+  delegate_to: "{{ nova_compute_drain_delegate_host }}"
+  environment: "{{ openstack_auth_env }}"
+  changed_when: false
+  vars:
+    ansible_host: "{{ hostvars[nova_compute_drain_delegate_host].ansible_host }}"
+
+- name: Set fact containing list of instances
+  set_fact:
+    nova_compute_drain_instance_info: "{{ instances.stdout | from_json }}"

roles/nova_compute_drain/tasks/live-migrate.yml

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+---
+
+- name: "Live migrate instance: {{ instance_uuid }}"  # noqa no-changed-when
+  command: >
+    {{ nova_compute_drain_venv }}/bin/openstack
+    --os-compute-api-version 2.25
+    server migrate
+    {{ instance_uuid }}
+    --live-migration
+    --wait
+  delegate_to: "{{ nova_compute_drain_delegate_host }}"
+  environment: "{{ openstack_auth_env }}"
+  vars:
+    ansible_host: "{{ hostvars[nova_compute_drain_delegate_host].ansible_host }}"
+  register: result
+  failed_when:
+    - result is failed

roles/nova_compute_drain/tasks/main.yml

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+---
+- include_tasks: setup.yml
+
+- include_tasks: instance-info.yml
+
+- include_tasks: live-migrate.yml
+  loop: "{{ nova_compute_drain_instance_info | selectattr('Status', 'equalto', 'ACTIVE') | list }}"
+  loop_control:
+    label: "{{ item.ID | default }}"
+  vars:
+    instance_uuid: "{{ item.ID | default }}"
+
+- include_tasks: cold-migrate.yml
+  loop: "{{ nova_compute_drain_instance_info | selectattr('Status', 'equalto', 'SHUTOFF') | list }}"
+  loop_control:
+    label: "{{ item.ID | default }}"
+  vars:
+    instance_uuid: "{{ item.ID | default }}"
+
+- include_tasks: instance-info.yml
+
+- name: Fail if there are instances still on the host
+  fail:
+    msg: >
+      Instances still on {{ inventory_hostname }}: {{ instances.stdout | from_json }}
+  when:
+    - nova_compute_migration_fatal | bool
+    - nova_compute_drain_instance_info | length > 0

roles/nova_compute_drain/tasks/setup.yml

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+---
+
+- name: Initiate openstack cli virtualenv  # noqa package-latest
+  pip:
+    virtualenv: "{{ nova_compute_drain_venv }}"
+    name:
+      - pip
+      - setuptools
+    state: latest
+    virtualenv_command: /usr/bin/python3.6 -m venv
+  delegate_to: "{{ nova_compute_drain_delegate_host }}"
+  vars:
+    # NOTE: Without this, the delegate ansible_host variable will not
+    # be respected when using delegate_to.
+    ansible_host: "{{ hostvars[nova_compute_drain_delegate_host].ansible_host | default(nova_compute_drain_delegate_host) }}"
+
+- name: Install openstack CLI tools in virtualenv
+  pip:
+    virtualenv: "{{ nova_compute_drain_venv }}"
+    name:
+      - python-openstackclient
+    extra_args: "{% if pip_upper_constraints_file %}-c {{ pip_upper_constraints_file }}{% endif %}"
+  delegate_to: "{{ nova_compute_drain_delegate_host }}"
+  vars:
+    # NOTE: Without this, the delegate's ansible_host variable will not
+    # be respected when using delegate_to.
+    ansible_host: "{{ hostvars[nova_compute_drain_delegate_host].ansible_host | default(nova_compute_drain_delegate_host) }}"