Added overlayfs backend type to the lxc_container module

This commit adds the overlayfs type to the lxc_container module. In
Adding the overlayfs type the commit adds the ability to clone a
container. While cloning is not locked down to only the overlayfs
container backend it is of particular interest when using the overlayfs
backend as it provides for amazingly fast snapshots.

Changes to the resource types and documentation have been added on how
the new backend type can be used along with the clone operation.

This PR addresses a question asked on the original merged pull request
for overlayfs support which came from @fghaas on PR
"https://github.com/ansible/ansible-modules-extras/pull/123".

The overlayfs archive function is a first class function and will
allow for the containers to be backed-up using all methods which
brings support up to that of all other storage backends.

lib/ansible/modules/extras/cloud/lxc/lxc_container.py

@@ -38,6 +38,7 @@ options:
           - lvm
           - loop
           - btrfs
+          - overlayfs
         description:
           - Backend storage type for the container.
         required: false
@@ -112,6 +113,20 @@ options:
           - Set the log level for a container where *container_log* was set.
         required: false
         default: INFO
+    clone_name:
+        description:
+          - Name of the new cloned server. This is only used when state is
+            clone.
+        required: false
+    clone_snapshot:
+        choices:
+          - true
+          - false
+        description:
+          - Create a snapshot a container when cloning. This is not supported
+            by all container storage backends. Enabling this may fail if the
+            backing store does not support snapshots.
+        default: false
     archive:
         choices:
           - true
@@ -141,8 +156,12 @@ options:
           - restarted
           - absent
           - frozen
+          - clone
         description:
-          - Start a container right after it's created.
+          - Define the state of a container. If you use clone the container
+            will be stopped while the clone operation is happening and upon
+            completion of the clone the original container state will be
+            restored.
         required: false
         default: started
     container_config:
@@ -298,6 +317,47 @@ EXAMPLES = """
     archive: true
     archive_path: /opt/archives
 
+- name: Create an overlayfs container
+  lxc_container:
+    name: test-container-overlayfs
+    container_log: true
+    template: ubuntu
+    state: started
+    backing_store: overlayfs
+    template_options: --release trusty
+
+- name: Clone a container
+  lxc_container:
+    name: test-container-overlayfs
+    clone_name: test-container-clone
+    state: clone
+
+- name: Clone a container using snapshot.
+  lxc_container:
+    name: test-container-overlayfs
+    clone_name: test-container-overlayfs-clone
+    backing_store: overlayfs
+    clone_snapshot: true
+    state: clone
+
+- name: Create a new container and clone it
+  lxc_container:
+    name: test-container-new-overlayfs
+    clone_name: test-container-new-overlayfs-clone
+    backing_store: overlayfs
+    clone_snapshot: true
+    state: clone
+
+- name: Create a new container, clone it, and archive
+  lxc_container:
+    name: test-container-new-overlayfs
+    clone_name: test-container-new-overlayfs-clone
+    backing_store: overlayfs
+    clone_snapshot: true
+    state: clone
+    archive: true
+    archive_compression: gzip
+
 - name: Destroy a container.
   lxc_container:
     name: "{{ item }}"
@@ -308,6 +368,9 @@ EXAMPLES = """
     - test-container-frozen
     - test-container-lvm
     - test-container-config
+    - test-container-overlayfs
+    - test-container-clone
+    - test-container-overlayfs-clone
 """
 
 
@@ -354,6 +417,15 @@ LXC_COMMAND_MAP = {
             'directory': '--dir',
             'zfs_root': '--zfsroot'
         }
+    },
+    'clone': {
+        'variables': {
+            'backing_store': '--backingstore',
+            'lxc_path': '--lxcpath',
+            'fs_size': '--fssize',
+            'name': '--orig',
+            'clone_name': '--new'
+        }
     }
 }
 
@@ -372,6 +444,9 @@ LXC_BACKING_STORE = {
     ],
     'loop': [
         'lv_name', 'vg_name', 'thinpool', 'zfs_root'
+    ],
+    'overlayfs': [
+        'lv_name', 'vg_name', 'fs_type', 'fs_size', 'thinpool', 'zfs_root'
     ]
 }
 
@@ -391,7 +466,8 @@ LXC_ANSIBLE_STATES = {
     'stopped': '_stopped',
     'restarted': '_restarted',
     'absent': '_destroyed',
-    'frozen': '_frozen'
+    'frozen': '_frozen',
+    'clone': '_clone'
 }
 
 
@@ -505,15 +581,15 @@ class LxcContainerManagement(object):
         return num
 
     @staticmethod
-    def _container_exists(name):
+    def _container_exists(container_name):
         """Check if a container exists.
 
-        :param name: Name of the container.
+        :param container_name: Name of the container.
         :type: ``str``
         :returns: True or False if the container is found.
         :rtype: ``bol``
         """
-        if [i for i in lxc.list_containers() if i == name]:
+        if [i for i in lxc.list_containers() if i == container_name]:
             return True
         else:
             return False
@@ -546,6 +622,7 @@ class LxcContainerManagement(object):
         """
 
         # Remove incompatible storage backend options.
+        variables = variables.copy()
         for v in LXC_BACKING_STORE[self.module.params['backing_store']]:
             variables.pop(v, None)
 
@@ -658,6 +735,83 @@ class LxcContainerManagement(object):
                 self._container_startup()
                 self.container.freeze()
 
+    def _clone(self, count=0):
+        """Clone a new LXC container from an existing container.
+
+        This method will clone an existing container to a new container using
+        the `clone_name` variable as the new container name. The method will
+        create a container if the container `name` does not exist.
+
+        Note that cloning a container will ensure that the original container
+        is "stopped" before the clone can be done. Because this operation can
+        require a state change the method will return the original container
+        to its prior state upon completion of the clone.
+
+        Once the clone is complete the new container will be left in a stopped
+        state.
+        """
+
+        self.check_count(count=count, method='clone')
+        if self._container_exists(container_name=self.container_name):
+            # Ensure that the state of the original container is stopped
+            container_state = self._get_state()
+            if container_state != 'stopped':
+                self.state_change = True
+                self.container.stop()
+
+            build_command = [
+                self.module.get_bin_path('lxc-clone', True),
+            ]
+
+            build_command = self._add_variables(
+                variables_dict=self._get_vars(
+                    variables=LXC_COMMAND_MAP['clone']['variables']
+                ),
+                build_command=build_command
+            )
+
+            # Load logging for the instance when creating it.
+            if self.module.params.get('clone_snapshot') in BOOLEANS_TRUE:
+                build_command.append('--snapshot')
+
+            rc, return_data, err = self._run_command(build_command)
+            if rc != 0:
+                message = "Failed executing lxc-clone."
+                self.failure(
+                    err=err, rc=rc, msg=message, command=' '.join(
+                        build_command
+                    )
+                )
+            else:
+                self.state_change = True
+                # Restore the original state of the origin container if it was
+                # not in a stopped state.
+                if container_state == 'running':
+                    self.container.start()
+                elif container_state == 'frozen':
+                    self.container.start()
+                    self.container.freeze()
+
+            # Change the container name context to the new cloned container
+            # This enforces that the state of the new cloned container will be
+            # "stopped".
+            self.state = 'stopped'
+            self.container_name = self.module.params['clone_name']
+            self.container = self.get_container_bind()
+
+            # Return data
+            self._execute_command()
+
+            # Perform any configuration updates
+            self._config()
+
+            # Check if the container needs to have an archive created.
+            self._check_archive()
+        else:
+            self._create()
+            count += 1
+            self._clone(count)
+
     def _create(self):
         """Create a new LXC container.
 
@@ -712,9 +866,9 @@ class LxcContainerManagement(object):
 
         rc, return_data, err = self._run_command(build_command)
         if rc != 0:
-            msg = "Failed executing lxc-create."
+            message = "Failed executing lxc-create."
             self.failure(
-                err=err, rc=rc, msg=msg, command=' '.join(build_command)
+                err=err, rc=rc, msg=message, command=' '.join(build_command)
             )
         else:
             self.state_change = True
@@ -754,7 +908,7 @@ class LxcContainerManagement(object):
         :rtype: ``str``
         """
 
-        if self._container_exists(name=self.container_name):
+        if self._container_exists(container_name=self.container_name):
             return str(self.container.state).lower()
         else:
             return str('absent')
@@ -819,7 +973,7 @@ class LxcContainerManagement(object):
         """
 
         for _ in xrange(timeout):
-            if not self._container_exists(name=self.container_name):
+            if not self._container_exists(container_name=self.container_name):
                 break
 
             # Check if the container needs to have an archive created.
@@ -855,7 +1009,7 @@ class LxcContainerManagement(object):
         """
 
         self.check_count(count=count, method='frozen')
-        if self._container_exists(name=self.container_name):
+        if self._container_exists(container_name=self.container_name):
             self._execute_command()
 
             # Perform any configuration updates
@@ -889,7 +1043,7 @@ class LxcContainerManagement(object):
         """
 
         self.check_count(count=count, method='restart')
-        if self._container_exists(name=self.container_name):
+        if self._container_exists(container_name=self.container_name):
             self._execute_command()
 
             # Perform any configuration updates
@@ -916,7 +1070,7 @@ class LxcContainerManagement(object):
         """
 
         self.check_count(count=count, method='stop')
-        if self._container_exists(name=self.container_name):
+        if self._container_exists(container_name=self.container_name):
             self._execute_command()
 
             # Perform any configuration updates
@@ -943,7 +1097,7 @@ class LxcContainerManagement(object):
         """
 
         self.check_count(count=count, method='start')
-        if self._container_exists(name=self.container_name):
+        if self._container_exists(container_name=self.container_name):
             container_state = self._get_state()
             if container_state == 'running':
                 pass
@@ -1010,18 +1164,18 @@ class LxcContainerManagement(object):
         all_lvms = [i.split() for i in stdout.splitlines()][1:]
         return [lv_entry[0] for lv_entry in all_lvms if lv_entry[1] == vg]
 
-    def _get_vg_free_pe(self, name):
+    def _get_vg_free_pe(self, vg_name):
         """Return the available size of a given VG.
 
-        :param name: Name of volume.
-        :type name: ``str``
+        :param vg_name: Name of volume.
+        :type vg_name: ``str``
         :returns: size and measurement of an LV
         :type: ``tuple``
         """
 
         build_command = [
             'vgdisplay',
-            name,
+            vg_name,
             '--units',
             'g'
         ]
@@ -1030,7 +1184,7 @@ class LxcContainerManagement(object):
             self.failure(
                 err=err,
                 rc=rc,
-                msg='failed to read vg %s' % name,
+                msg='failed to read vg %s' % vg_name,
                 command=' '.join(build_command)
             )
 
@@ -1039,17 +1193,17 @@ class LxcContainerManagement(object):
         _free_pe = free_pe[0].split()
         return float(_free_pe[-2]), _free_pe[-1]
 
-    def _get_lv_size(self, name):
+    def _get_lv_size(self, lv_name):
         """Return the available size of a given LV.
 
-        :param name: Name of volume.
-        :type name: ``str``
+        :param lv_name: Name of volume.
+        :type lv_name: ``str``
         :returns: size and measurement of an LV
         :type: ``tuple``
         """
 
         vg = self._get_lxc_vg()
-        lv = os.path.join(vg, name)
+        lv = os.path.join(vg, lv_name)
         build_command = [
             'lvdisplay',
             lv,
@@ -1083,7 +1237,7 @@ class LxcContainerManagement(object):
         """
 
         vg = self._get_lxc_vg()
-        free_space, messurement = self._get_vg_free_pe(name=vg)
+        free_space, messurement = self._get_vg_free_pe(vg_name=vg)
 
         if free_space < float(snapshot_size_gb):
             message = (
@@ -1186,25 +1340,25 @@ class LxcContainerManagement(object):
 
         return archive_name
 
-    def _lvm_lv_remove(self, name):
+    def _lvm_lv_remove(self, lv_name):
         """Remove an LV.
 
-        :param name: The name of the logical volume
-        :type name: ``str``
+        :param lv_name: The name of the logical volume
+        :type lv_name: ``str``
         """
 
         vg = self._get_lxc_vg()
         build_command = [
             self.module.get_bin_path('lvremove', True),
             "-f",
-            "%s/%s" % (vg, name),
+            "%s/%s" % (vg, lv_name),
         ]
         rc, stdout, err = self._run_command(build_command)
         if rc != 0:
             self.failure(
                 err=err,
                 rc=rc,
-                msg='Failed to remove LVM LV %s/%s' % (vg, name),
+                msg='Failed to remove LVM LV %s/%s' % (vg, lv_name),
                 command=' '.join(build_command)
             )
 
@@ -1216,31 +1370,71 @@ class LxcContainerManagement(object):
         :param temp_dir: path to the temporary local working directory
         :type temp_dir: ``str``
         """
+        # This loop is created to support overlayfs archives. This should
+        # squash all of the layers into a single archive.
+        fs_paths = container_path.split(':')
+        if 'overlayfs' in fs_paths:
+            fs_paths.pop(fs_paths.index('overlayfs'))
+
+        for fs_path in fs_paths:
+            # Set the path to the container data
+            fs_path = os.path.dirname(fs_path)
+
+            # Run the sync command
+            build_command = [
+                self.module.get_bin_path('rsync', True),
+                '-aHAX',
+                fs_path,
+                temp_dir
+            ]
+            rc, stdout, err = self._run_command(
+                build_command,
+                unsafe_shell=True
+            )
+            if rc != 0:
+                self.failure(
+                    err=err,
+                    rc=rc,
+                    msg='failed to perform archive',
+                    command=' '.join(build_command)
+                )
+
+    def _unmount(self, mount_point):
+        """Unmount a file system.
+
+        :param mount_point: path on the file system that is mounted.
+        :type mount_point: ``str``
+        """
 
         build_command = [
-            self.module.get_bin_path('rsync', True),
-            '-aHAX',
-            container_path,
-            temp_dir
+            self.module.get_bin_path('umount', True),
+            mount_point,
         ]
-        rc, stdout, err = self._run_command(build_command, unsafe_shell=True)
+        rc, stdout, err = self._run_command(build_command)
         if rc != 0:
             self.failure(
                 err=err,
                 rc=rc,
-                msg='failed to perform archive',
+                msg='failed to unmount [ %s ]' % mount_point,
                 command=' '.join(build_command)
             )
 
-    def _unmount(self, mount_point):
-        """Unmount a file system.
+    def _overlayfs_mount(self, lowerdir, upperdir, mount_point):
+        """mount an lv.
 
+        :param lowerdir: name/path of the lower directory
+        :type lowerdir: ``str``
+        :param upperdir: name/path of the upper directory
+        :type upperdir: ``str``
         :param mount_point: path on the file system that is mounted.
         :type mount_point: ``str``
         """
 
         build_command = [
-            self.module.get_bin_path('umount', True),
+            self.module.get_bin_path('mount', True),
+            '-t overlayfs',
+            '-o lowerdir=%s,upperdir=%s' % (lowerdir, upperdir),
+            'overlayfs',
             mount_point,
         ]
         rc, stdout, err = self._run_command(build_command)
@@ -1248,8 +1442,8 @@ class LxcContainerManagement(object):
             self.failure(
                 err=err,
                 rc=rc,
-                msg='failed to unmount [ %s ]' % mount_point,
-                command=' '.join(build_command)
+                msg='failed to mount overlayfs:%s:%s to %s -- Command: %s'
+                    % (lowerdir, upperdir, mount_point, build_command)
             )
 
     def _container_create_tar(self):
@@ -1278,13 +1472,15 @@ class LxcContainerManagement(object):
 
         # Test if the containers rootfs is a block device
         block_backed = lxc_rootfs.startswith(os.path.join(os.sep, 'dev'))
+
+        # Test if the container is using overlayfs
+        overlayfs_backed = lxc_rootfs.startswith('overlayfs')
+
         mount_point = os.path.join(work_dir, 'rootfs')
 
         # Set the snapshot name if needed
         snapshot_name = '%s_lxc_snapshot' % self.container_name
 
-        # Set the path to the container data
-        container_path = os.path.dirname(lxc_rootfs)
         container_state = self._get_state()
         try:
             # Ensure the original container is stopped or frozen
@@ -1295,7 +1491,7 @@ class LxcContainerManagement(object):
                     self.container.stop()
 
             # Sync the container data from the container_path to work_dir
-            self._rsync_data(container_path, temp_dir)
+            self._rsync_data(lxc_rootfs, temp_dir)
 
             if block_backed:
                 if snapshot_name not in self._lvm_lv_list():
@@ -1304,7 +1500,7 @@ class LxcContainerManagement(object):
 
                     # Take snapshot
                     size, measurement = self._get_lv_size(
-                        name=self.container_name
+                        lv_name=self.container_name
                     )
                     self._lvm_snapshot_create(
                         source_lv=self.container_name,
@@ -1325,25 +1521,33 @@ class LxcContainerManagement(object):
                             ' up old snapshot of containers before continuing.'
                             % snapshot_name
                     )
-
-            # Restore original state of container
-            if container_state == 'running':
-                if self._get_state() == 'frozen':
-                    self.container.unfreeze()
-                else:
-                    self.container.start()
+            elif overlayfs_backed:
+                lowerdir, upperdir = lxc_rootfs.split(':')[1:]
+                self._overlayfs_mount(
+                    lowerdir=lowerdir,
+                    upperdir=upperdir,
+                    mount_point=mount_point
+                )
 
             # Set the state as changed and set a new fact
             self.state_change = True
             return self._create_tar(source_dir=work_dir)
         finally:
-            if block_backed:
+            if block_backed or overlayfs_backed:
                 # unmount snapshot
                 self._unmount(mount_point)
 
+            if block_backed:
                 # Remove snapshot
                 self._lvm_lv_remove(snapshot_name)
 
+            # Restore original state of container
+            if container_state == 'running':
+                if self._get_state() == 'frozen':
+                    self.container.unfreeze()
+                else:
+                    self.container.start()
+
             # Remove tmpdir
             shutil.rmtree(temp_dir)
 
@@ -1453,6 +1657,14 @@ def main():
                 choices=[n for i in LXC_LOGGING_LEVELS.values() for n in i],
                 default='INFO'
             ),
+            clone_name=dict(
+                type='str',
+                required=False
+            ),
+            clone_snapshot=dict(
+                choices=BOOLEANS,
+                default='false'
+            ),
             archive=dict(
                 choices=BOOLEANS,
                 default='false'
@@ -1480,4 +1692,3 @@ def main():
 # import module bits
 from ansible.module_utils.basic import *
 main()
-