ec2_vol supports name / id to mount volume on instance

* volume_size no longer required if name/id are provided
* id is volume-id
* name is volume Name tag
* special checking is provided

cloud/ec2_vol

@@ -46,6 +46,18 @@ options:
     required: false
     default: null 
     aliases: []
+  name:
+    description:
+      - volume Name tag if you wish to attach an existing volume (requires instance)
+    required: false
+    default: null
+    aliases: []
+  name:
+    description:
+      - volume id if you wish to attach an existing volume (requires instance)
+    required: false
+    default: null
+    aliases: []
   volume_size:
     description:
       - size of volume (in GB) to create.
@@ -122,6 +134,26 @@ EXAMPLES = '''
     volume_size: 5
     with_items: ec2.instances
     register: ec2_vol
+
+# Idempotent playbook example combined with single instance launch
+# Volume must exist in the same zone; will not do anything if it is
+# already attached.
+- local_action: 
+    module: ec2 
+    keypair: "{{ keypair }}"
+    image: "{{ image }}"
+    zone: YYYYYY
+    id: my_instance
+    wait: yes 
+    count: 1
+    register: ec2
+- local_action: 
+    module: ec2_vol 
+    instance: "{{ item.id }}" 
+    name: my_existing_volume_Name_tag
+    device_name: /dev/xvdf
+    with_items: ec2.instances
+    register: ec2_vol
 '''
 
 # Note: this module needs to be made idempotent. Possible solution is to use resource tags with the volumes.
@@ -142,7 +174,9 @@ def main():
     module = AnsibleModule(
         argument_spec = dict(
             instance = dict(),
-            volume_size = dict(required=True),
+            id = dict(),
+            name = dict(),
+            volume_size = dict(),
             iops = dict(),
             device_name = dict(),
             region = dict(aliases=['aws_region', 'ec2_region'], choices=AWS_REGIONS),
@@ -154,20 +188,27 @@ def main():
         )
     )
 
+    id = module.params.get('id')
+    name = module.params.get('name')
     instance = module.params.get('instance')
     volume_size = module.params.get('volume_size')
     iops = module.params.get('iops')
     device_name = module.params.get('device_name')
     zone = module.params.get('zone')
     snapshot = module.params.get('snapshot')
-   
+
     ec2 = ec2_connect(module)
 
+    if id and name:
+        module.fail_json(msg="Both id and name cannot be specified")
+
+    if not (id or name or volume_size):
+        module.fail_json(msg="Cannot specify volume_size and either one of name or id")
+
     # Here we need to get the zone info for the instance. This covers situation where 
     # instance is specified but zone isn't.
     # Useful for playbooks chaining instance launch with volume create + attach and where the
     # zone doesn't matter to the user.
-
     if instance:
         reservation = ec2.get_all_instances(instance_ids=instance)
         inst = reservation[0].instances[0]
@@ -189,14 +230,51 @@ def main():
         volume_type = 'standard'
 
     # If no instance supplied, try volume creation based on module parameters.
+    if name or id:
+        if not instance:
+            module.fail_json(msg = "If name or id is specified, instance must also be specified")
+        if iops or volume_size:
+            module.fail_json(msg = "Parameters are not compatible: [id or name] and [iops or volume_size]")
+
+        filters = {}
+        volume_ids = None
+        if zone:
+            filters['availability_zone'] = zone
+        if name:
+            filters = {'tag:Name': name}
+        if id:
+            volume_ids = [id]
+        try:
+            vols = ec2.get_all_volumes(volume_ids=volume_ids, filters=filters)
+        except boto.exception.BotoServerError, e:
+            module.fail_json(msg = "%s: %s" % (e.error_code, e.error_message))
+
+        if not vols:
+            module.fail_json(msg = "Could not find volume in zone (if specified): %s" % name or id)
+        if len(vols) > 1:
+            module.fail_json(msg =
+               "Found more than one volume in zone (if specified) with name: %s" % name)
 
-    try:
-        volume = ec2.create_volume(volume_size, zone, snapshot, volume_type, iops)
-        while volume.status != 'available':
-            time.sleep(3)
-            volume.update()
-    except boto.exception.BotoServerError, e:
-        module.fail_json(msg = "%s: %s" % (e.error_code, e.error_message))
+        volume = vols.pop()
+        if volume.attachment_state() is not None:
+            adata = volume.attach_data
+            if adata.instance_id != instance:
+                module.fail_json(msg = "Volume %s is already attached to another instance: %s"
+                                 % (name or id, adata.instance_id))
+            else:
+                module.exit_json(msg="Volume %s is already mapped on instance %s: %s" %
+                                 (name or id, adata.instance_id, adata.device),
+                                 volume_id=id,
+                                 device=adata.device,
+                                 changed=False)
+    else:
+        try:
+            volume = ec2.create_volume(volume_size, zone, snapshot, volume_type, iops)
+            while volume.status != 'available':
+                time.sleep(3)
+                volume.update()
+        except boto.exception.BotoServerError, e:
+            module.fail_json(msg = "%s: %s" % (e.error_code, e.error_message))
 
     # Attach the created volume.
 
@@ -207,16 +285,15 @@ def main():
                 time.sleep(3)
                 volume.update()
         except boto.exception.BotoServerError, e:
-            module.fail_json(msg = "%s: %s" % (e.error_code, e.error_message))           
-   
+            module.fail_json(msg = "%s: %s" % (e.error_code, e.error_message))
+
     # If device_name isn't set, make a choice based on best practices here:
     # http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/block-device-mapping-concepts.html
-    
+
     # In future this needs to be more dynamic but combining block device mapping best practices
     # (bounds for devices, as above) with instance.block_device_mapping data would be tricky. For me ;)
 
     # Use password data attribute to tell whether the instance is Windows or Linux
-
     if device_name is None and instance:
         try:
             if not ec2.get_password_data(inst.id):