diff --git a/roles/common/defaults/main.yml b/roles/common/defaults/main.yml
index c54c799b891625f0f0e32e8db94e329f87435f6f..29db9f6282f696abbefc6fb48d91e7a5accc9269 100644
--- a/roles/common/defaults/main.yml
+++ b/roles/common/defaults/main.yml
@@ -1,6 +1,6 @@
 ---
 
-enable_backup: False
+enable_backup: false
 common_packages: []
 os_users: []
 os_groups: []
diff --git a/roles/common/molecule/default/create.yml b/roles/common/molecule/default/create.yml
index f8eb37cd4df02c540216c02791d0c50870986202..ce8657f9bae3be7f42731fd1efe77e87a62afcd9 100644
--- a/roles/common/molecule/default/create.yml
+++ b/roles/common/molecule/default/create.yml
@@ -2,7 +2,7 @@
 - name: Create
   hosts: localhost
   connection: local
-  gather_facts: False
+  gather_facts: false
   no_log: "{{ not lookup('env', 'MOLECULE_DEBUG') | bool }}"
   vars:
     molecule_file: "{{ lookup('env', 'MOLECULE_FILE') }}"
diff --git a/roles/common/molecule/default/destroy.yml b/roles/common/molecule/default/destroy.yml
index 3972a2df8fafe515b30a74f951499b83aae8449c..8f0a3703672765e77f4f1a3a8046a1f2b561a7a8 100644
--- a/roles/common/molecule/default/destroy.yml
+++ b/roles/common/molecule/default/destroy.yml
@@ -3,7 +3,7 @@
 - name: Destroy
   hosts: localhost
   connection: local
-  gather_facts: False
+  gather_facts: false
   no_log: "{{ not lookup('env', 'MOLECULE_DEBUG') | bool }}"
   vars:
     molecule_file: "{{ lookup('env', 'MOLECULE_FILE') }}"
diff --git a/roles/common/molecule/default/group_vars/parameters-mandatory.yml b/roles/common/molecule/default/group_vars/parameters-mandatory.yml
new file mode 100644
index 0000000000000000000000000000000000000000..ed97d539c095cf1413af30cc23dea272095b97dd
--- /dev/null
+++ b/roles/common/molecule/default/group_vars/parameters-mandatory.yml
@@ -0,0 +1 @@
+---
diff --git a/roles/common/molecule/default/group_vars/parameters-optional.yml b/roles/common/molecule/default/group_vars/parameters-optional.yml
new file mode 100644
index 0000000000000000000000000000000000000000..23aa5cd33714bdcb21712593ef6ee85264e28502
--- /dev/null
+++ b/roles/common/molecule/default/group_vars/parameters-optional.yml
@@ -0,0 +1,61 @@
+---
+
+enable_backup: true
+apt_proxy: "http://10.31.127.2:3142/"
+os_users:
+  - name: user1
+  - name: user2
+    uid: 2001
+    additional_groups:
+      - group1
+      - group2
+    authorized_keys:
+      - "{{ lookup('file', 'tests/data/ssh/clientkey1.pub') }}"
+      - "{{ lookup('file', 'tests/data/ssh/clientkey2.pub') }}"
+    # Password is 'user2'.
+    password: "$6$wdXOQiMe09ugh0$VRIph2XA2QQyEYlAlH7zT4TPACDUalf/4FKpqG9JRHfKxANTcTug2ANCt450htcs0LikJfHLWofLP54jraFU61"
+  - name: user3
+    uid: 2002
+    additional_groups:
+      - group3
+    authorized_keys:
+      - "{{ lookup('file', 'tests/data/ssh/clientkey3.pub') }}"
+    # Password is 'user3'.
+    password: "$6$nmx.21uLqT$9LrUqNUgUwIM.l0KFKgr2.kDEwe2lo7IbBIhnG70AGW7GTFdWBUFnGAxH15YxikTXhDJD/uxd.NNgojEOjRvx1"
+os_groups:
+  - name: group1
+  - name: group2
+    gid: 3001
+  - name: group3
+    gid: 3002
+common_packages:
+  - units
+  - gnutls-bin
+  - "{{ 'libmariadb-client-lgpl-dev-compat' if ansible_distribution_release == 'jessie'
+  else 'libmariadbclient-dev-compat' if ansible_distribution_release == 'stretch' }}"
+  - emacs24-nox
+ca_certificates:
+  cacert1: "{{ lookup('file', 'tests/data/x509/ca1.cert.pem') }}"
+  cacert2: "{{ lookup('file', 'tests/data/x509/ca2.cert.pem') }}"
+extra_backup_patterns:
+  - /home/user1
+  - /home/user2
+incoming_connection_limit: 5/second
+incoming_connection_limit_burst: 5
+pipreqcheck_uid: 2500
+pipreqcheck_gid: 2500
+prompt_colour: cyan
+prompt_id: test
+# Purposefully set this to 3 servers to make sure we are
+# overriding the default configuration.
+ntp_servers:
+  - "0.debian.pool.ntp.org"
+  - "1.debian.pool.ntp.org"
+  - "2.debian.pool.ntp.org"
+# From backup_client role meta dependency.
+backup_encryption_key: "{{ lookup('file', 'tests/data/gnupg/backup_encryption_key') }}"
+backup_server: backup-server
+backup_server_host_ssh_public_keys:
+  - bougs-backup-server-key-1
+  - bougs-backup-server-key-2
+backup_ssh_key: "bogus-backup-client-key"
diff --git a/roles/common/molecule/default/molecule.yml b/roles/common/molecule/default/molecule.yml
index 4e1aafd942b349d48dcda9d3cef3e0f47cac0743..551efe9253b27b809664125e70d9e81774da7efe 100644
--- a/roles/common/molecule/default/molecule.yml
+++ b/roles/common/molecule/default/molecule.yml
@@ -9,6 +9,8 @@ driver:
 
 lint:
   name: yamllint
+  options:
+    config-file: ../../.yamllint.yml
 
 platforms:
   - name: helper
diff --git a/roles/common/molecule/default/playbook.yml b/roles/common/molecule/default/playbook.yml
index eb0cc6b215a3cbe3554b8d49dae65a2ba4e67604..dc3adc6f7d043986309e2cab6cbfa4186b613488 100644
--- a/roles/common/molecule/default/playbook.yml
+++ b/roles/common/molecule/default/playbook.yml
@@ -1,7 +1,7 @@
 ---
 
 - hosts: helper
-  become: yes
+  become: true
   tasks:
 
     - name: Install apt-cacher-ng
@@ -9,70 +9,7 @@
         name: apt-cacher-ng
         state: installed
 
-- hosts: parameters-mandatory
-  become: yes
+- hosts: parameters-mandatory,parameters-optional
+  become: true
   roles:
-    - role: common
-
-- hosts: parameters-optional
-  become: yes
-  roles:
-    - role: common
-      enable_backup: yes
-      apt_proxy: "http://10.31.127.2:3142/"
-      os_users:
-        - name: user1
-        - name: user2
-          uid: 2001
-          additional_groups:
-            - group1
-            - group2
-          authorized_keys:
-            - "{{ lookup('file', 'tests/data/ssh/clientkey1.pub') }}"
-            - "{{ lookup('file', 'tests/data/ssh/clientkey2.pub') }}"
-          # Password is 'user2'.
-          password: "$6$wdXOQiMe09ugh0$VRIph2XA2QQyEYlAlH7zT4TPACDUalf/4FKpqG9JRHfKxANTcTug2ANCt450htcs0LikJfHLWofLP54jraFU61"
-        - name: user3
-          uid: 2002
-          additional_groups:
-            - group3
-          authorized_keys:
-            - "{{ lookup('file', 'tests/data/ssh/clientkey3.pub') }}"
-          # Password is 'user3'.
-          password: "$6$nmx.21uLqT$9LrUqNUgUwIM.l0KFKgr2.kDEwe2lo7IbBIhnG70AGW7GTFdWBUFnGAxH15YxikTXhDJD/uxd.NNgojEOjRvx1"
-      os_groups:
-        - name: group1
-        - name: group2
-          gid: 3001
-        - name: group3
-          gid: 3002
-      common_packages:
-        - units
-        - gnutls-bin
-        - "{{ 'libmariadb-client-lgpl-dev-compat' if ansible_distribution_release == 'jessie' else 'libmariadbclient-dev-compat' if ansible_distribution_release == 'stretch' }}"
-        - emacs24-nox
-      ca_certificates:
-        cacert1: "{{ lookup('file', 'tests/data/x509/ca1.cert.pem') }}"
-        cacert2: "{{ lookup('file', 'tests/data/x509/ca2.cert.pem') }}"
-      extra_backup_patterns:
-        - /home/user1
-        - /home/user2
-      incoming_connection_limit: 5/second
-      incoming_connection_limit_burst: 5
-      pipreqcheck_uid: 2500
-      pipreqcheck_gid: 2500
-      prompt_colour: cyan
-      prompt_id: test
-      # Purposefully set this to 3 servers to make sure we are
-      # overriding the default configuration.
-      ntp_servers:
-        - "0.debian.pool.ntp.org"
-        - "1.debian.pool.ntp.org"
-        - "2.debian.pool.ntp.org"
-      # From backup_client role meta dependency.
-      backup_encryption_key: "{{ lookup('file', 'tests/data/gnupg/backup_encryption_key') }}"
-      backup_server: backup-server
-      backup_server_host_ssh_public_keys:
-        - bougs-backup-server-key-1
-        - bougs-backup-server-key-2
-      backup_ssh_key: "bogus-backup-client-key"
+    - common
diff --git a/roles/common/molecule/default/prepare.yml b/roles/common/molecule/default/prepare.yml
index da6db4aeb78655b297d2acdacfbd877e045955f3..59567b5e85a899689a70209645fc87dbbbbdcaf3 100644
--- a/roles/common/molecule/default/prepare.yml
+++ b/roles/common/molecule/default/prepare.yml
@@ -2,22 +2,22 @@
 
 - name: Prepare
   hosts: all
-  gather_facts: False
+  gather_facts: false
   tasks:
 
     - name: Install python for Ansible
       raw: test -e /usr/bin/python || (apt -y update && apt install -y python-minimal)
-      become: True
-      changed_when: False
+      become: true
+      changed_when: false
 
 - hosts: all
-  become: yes
+  become: true
   tasks:
 
     - name: Update all caches to avoid errors due to missing remote archives
       apt:
-        update_cache: yes
-      changed_when: False
+        update_cache: true
+      changed_when: false
 
     - name: Install net-tools for running Testinfra host.socket tests
       apt:
diff --git a/roles/common/tasks/main.yml b/roles/common/tasks/main.yml
index d04ee6e5e876aa8aff391764d1d3a5f43ce2b7b3..dc48754070199fb602cc1f7a2672f5d11eaad892 100644
--- a/roles/common/tasks/main.yml
+++ b/roles/common/tasks/main.yml
@@ -29,7 +29,7 @@
   lineinfile:
     dest: "/etc/login.defs"
     state: present
-    backrefs: yes
+    backrefs: true
     regexp: '^UMASK(\s+)'
     line: 'UMASK\g<1>027'
 
@@ -37,7 +37,7 @@
   lineinfile:
     dest: "/etc/adduser.conf"
     state: present
-    backrefs: yes
+    backrefs: true
     regexp: '^DIR_MODE='
     line: 'DIR_MODE=0750'
 
@@ -139,7 +139,7 @@
     uid: "{{ item.uid | default(omit) }}"
     group: "{{ item.name }}"
     groups: "{{ ','.join(item.additional_groups | default([])) }}"
-    append: yes
+    append: true
     shell: /bin/bash
     state: present
     password: "{{ item.password | default('!') }}"
@@ -308,7 +308,7 @@
   command: "/usr/bin/virtualenv --prompt '(pipreqcheck)' '/var/lib/pipreqcheck/virtualenv'"
   args:
     creates: '/var/lib/pipreqcheck/virtualenv/bin/activate'
-  become: yes
+  become: true
   become_user: "pipreqcheck"
   tags:
     # [ANSIBLE0012] Commands should not change things if nothing needs doing
@@ -353,7 +353,7 @@
     name:
       - "pip>=9.0.0,<10.0.0"
     virtualenv: "~pipreqcheck/virtualenv"
-  become: yes
+  become: true
   become_user: "pipreqcheck"
 
 - name: Install pip-tools if not present
@@ -361,14 +361,14 @@
     name: pip-tools
     state: present
     virtualenv: "~pipreqcheck/virtualenv"
-  become: yes
+  become: true
   become_user: "pipreqcheck"
 
 - name: Synchronise pip-tools virtual environment via deployed requirements file
   shell: "source ~pipreqcheck/virtualenv/bin/activate && pip-sync /etc/pip_check_requirements_upgrades/pipreqcheck/requirements.txt"
   args:
     executable: /bin/bash
-  become: yes
+  become: true
   become_user: "pipreqcheck"
   register: pipreqcheck_pip_sync
   changed_when: "pipreqcheck_pip_sync.stdout != 'Everything up-to-date'"