OPS-1385 role for mounting/formatting volumes

This implements a role that consumes a volume list of dicts and ensures
those are all mounted in the expected location on your system as well as
formatting any drives with the wrong fstype.

As a safety feature, it defaults to being unwilling to unmount drives
(since that might result in data loss or mismanagement) and there is a
flag you can -e to enable it.

It is assumed you will run this role passing along your volume list from
your main playbook and secure vars.

playbooks/roles/mount_ebs/defaults/main.yml

+# Expects a list of dicts with these keys
+#  - device: /dev/xvdk
+#    mount: /edx/var/mongo
+#    options: "defaults,noatime"
+#    fstype: ext4
+# While mount, options and fstype are pretty standard in our app, the device names
+# will be highly dependent on how you stand up your instances.
+#
+# Additionally - order is important if you have child directories.  If you want to mount
+# /edx/var/mongo and /edx/var/mongo/mongodb/journal, you must specify them in that order,
+# otherwise this role will mount /edx/var/mongo over the top of /edx/var/mongo/mongodb/journal
+# which is not what you wanted.
+volumes: []
+
+UNMOUNT_DISKS: false

playbooks/roles/mount_ebs/tasks/main.yml

+#
+# edX Configuration
+#
+# github:     https://github.com/edx/configuration
+# wiki:       https://github.com/edx/configuration/wiki
+# code style: https://github.com/edx/configuration/wiki/Ansible-Coding-Conventions
+# license:    https://github.com/edx/configuration/blob/master/LICENSE.TXT
+#
+#
+#
+# Tasks for role mount_dbs
+#
+# Overview:
+#
+# This role ensures that the correct EBS volumes are mounted to the right locations.
+# If the volumes are already mounted to the correct place, this role does nothing.
+
+# This task will be skipped if UNMOUNT_DISKS is false, causing the next task
+# to error if the disk has the wrong fstype but is already mounted
+- name: Unmount disk if fstype is wrong
+  mount:
+    name: "{{ (ansible_mounts | selectattr('device', 'equalto', item.device) | first | default({'mount': None})).mount }}"
+    src: "{{ (ansible_mounts | selectattr('device', 'equalto', item.device) | first | default({'device': None})).device }}"
+    fstype: "{{ (ansible_mounts | selectattr('device', 'equalto', item.device) | first | default({'fstype': None})).fstype }}"
+    state: unmounted
+  when: "{{ UNMOUNT_DISKS and (ansible_mounts | selectattr('device', 'equalto', item.device) | first | default({'fstype': None})).fstype != item.fstype }}"
+  with_items: volumes
+
+# Noop & reports "ok" if fstype is correct
+# Errors if fstype is wrong and disk is mounted (hence above task)
+- name: Create filesystem
+  filesystem:
+    dev: "{{ item.device }}"
+    fstype: "{{ item.fstype }}"
+    # Necessary because AWS gives some ephemeral disks the wrong fstype by default
+    force: true
+  with_items: volumes
+
+# This can fail if one volume is mounted on a child directory as another volume
+# and it attempts to unmount the parent first.  This is generally fixable by rerunning.
+# Order is super dependent here, but we're iterating ansible_mounts (in order to identify
+# all current mounts in the system) not volumes, which would be reversible.
+# Possibly fixable by saving this list of unmounts off and comparing it to volumes, but this
+# task rarely runs, since on server setup, the disks are unmounted, and in we won't
+# be unmounting disks unless you set UNMOUNT_DISKS to true.
+- name: Unmount disks mounted to the wrong place
+  mount:
+    name: "{{ item.mount }}"
+    src: "{{ item.device }}"
+    fstype: "{{ item.fstype }}"
+    state: unmounted
+  when: >
+    UNMOUNT_DISKS and
+    volumes | selectattr('device', 'equalto', item.device) | list | length != 0 and
+    (volumes | selectattr('device', 'equalto', item.device) | first).mount != item.mount
+  with_items: ansible_mounts
+# fail here if you attempted to unmount something instead of unmounting it
+# Meaning UNMOUNT disks is false, but the volumes indicates we should be fiddling mounts
+
+- name: Mount disks
+  mount:
+    name: "{{ item.mount }}"
+    src: "{{ item.device }}"
+    state: mounted
+    fstype: "{{ item.fstype }}"
+    opts: "{{ item.options }}"
+  with_items: volumes