2019独角兽企业重金招聘Python工程师标准>>> 
好处
开始之前先说下从卷启动虚拟机的好处，不然哪有动力去看呢？
从卷启动虚拟机的好处在于创建快照是通过调用卷管理接口（cinder），因而速度非常快。通过卷创建虚拟机，然后再创建快照是比较推荐的创建虚拟机快照方式，参见5分钟玩转openstack。
但是资料中并未就如何通过卷创建虚拟机给出说明，这篇文章以命令行操作形式，给出如何实现
实现步骤
要想实现从卷启动虚拟机总共分两步：
- 基于镜像创建启动卷
- 基于启动卷创建虚拟机
基于镜像创建启动卷
首先，查看以下可用的镜像，因为我们需要基于某个镜像来创建供创建虚拟机使用的启动卷
$ openstack image list
+--------------------------------------+------------------------------------+--------+
| ID | Name | Status |
+--------------------------------------+------------------------------------+--------+
| 1d9b293e-cba0-4306-80da-a6392cabe319 | CentOS 6 i386 | ACTIVE |
| 28c077ac-1352-4821-9f2c-dbc8855e9df1 | CentOS 6 x86_64 | ACTIVE |
| 64653f86-1897-4767-bf3a-e6416b4bb074 | CentOS 7 x86_64 (10/02/15) | ACTIVE |
| 787cba9d-bdbb-4f3a-9c39-50db9688faf5 | CentOS 7 x86_64 (12/02/15) | ACTIVE |
| a1ced3fb-af70-40f6-adbe-89e6301fdfd0 | CentOS 7 x86_64 (20/10/14) | ACTIVE |
| 24adac27-ca19-48e7-90b2-c38bc480693f | CoreOS | ACTIVE |
| 4a48c61e-bf88-4d82-bf07-52796700f22f | Debian 7 (20/10/14) | ACTIVE |
| 6cfef669-4897-4d19-aa7c-6f0087d7c13b | Fedora 19 i386 | ACTIVE |
| 011c9957-920f-4446-b7bf-8d60b15c6d54 | Fedora 19 x86_64 | ACTIVE |
| 769cf0aa-c5f2-4e69-8a49-70f9c9efcd93 | Fedora 20 x86_64 (29/09/14) | ACTIVE |
| 251557ed-ffc6-407d-ac93-110892445dc6 | Fedora 21 x86_64 (02/01/14) | ACTIVE |
| 63ba4a7a-0909-4e7b-b62e-f146f0140e8b | Ubuntu 12.04 i386 | ACTIVE |
| 8b20af24-1946-4fe5-a7c3-ad908c684712 | Ubuntu 12.04 x86_64 | ACTIVE |
| d3336991-3472-4ab6-8168-cac26f0b6d50 | Ubuntu 12.04 x86_64 (29/09/14) | ACTIVE |
| 249d6dc3-235e-4021-86a1-a3636ac3f134 | Ubuntu 14.04 x86_64 (29/09/14) | ACTIVE |
| a1718edf-f2b4-436a-9c06-af2630e09908 | Windows Server 2008 R2 | ACTIVE |
| fbd2a49a-d514-442e-a541-24ff0d539646 | Windows Server 2012 R2 | ACTIVE |
+--------------------------------------+------------------------------------+--------+
然后，通过调用命令来创建启动卷
$ openstack volume create --image 249d6dc3-235e-4021-86a1-a3636ac3f134 Ubuntu-14.04-15
+---------------------+--------------------------------------+
| Property | Value |
+---------------------+--------------------------------------+
| attachments | [] |
| availability_zone | nova |
| bootable | false |
| created_at | 2015-11-11T14:23:32.710621 |
| display_description | None |
| display_name | Ubuntu-14.04 |
| encrypted | False |
| id | d86de794-60cb-4725-8e8d-e9f4e097b63e |
| image_id | 249d6dc3-235e-4021-86a1-a3636ac3f134 |
| metadata | {} |
| size | 15 |
| snapshot_id | None |
| source_volid | None |
| status | creating |
| volume_type | None |
+---------------------+--------------------------------------+
等卷创建好后，卷的bootable属性会变成true
基于启动卷创建虚拟机
准备工作包含获取一个可用的flavor和network，过程如下：
$ openstack flavor list
+--------------------------------------+------------+-----------+------+-----------+-------+-----------+
| ID | Name | RAM | Disk | Ephemeral | VCPUs | Is_Public |
+--------------------------------------+------------+-----------+------+-----------+-------+-----------+
| 1791eb32-68a1-4ec9-ac8d-e2374ca9c909 | 1 GB | 1024 | 30 | 0 | 1 | True |
| 34719f08-452d-4e8d-a29f-548d82985477 | 4 GB - HC | 4096 | 60 | 0 | 4 | True |
| 569d85f5-647c-420d-98e6-85149e6eebf6 | 32 GB - HM | 32768 | 60 | 0 | 6 | True |
| 64c94219-1452-4934-a09a-d702c9370c3d | 8 GB - HM | 8192 | 60 | 0 | 2 | True |
| 677cac99-6a5a-4c6a-9884-23338d01c04d | 2 GB | 2048 | 60 | 0 | 1 | True |
| 75518817-da1b-4fbf-bd11-dffce8e73b49 | 8 GB - HC | 8192 | 60 | 0 | 8 | True |
| 885f9496-5de5-4894-bab9-98ef88e4892c | 8 GB | 8192 | 120 | 0 | 4 | True |
| b5ae8e6f-03f3-4146-9add-6e84e6944ead | 4 GB | 4096 | 80 | 0 | 2 | True |
| baec2dce-b1ea-4898-a259-9a3bf66f6262 | 512 MB | 512 | 10 | 0 | 1 | True |
| cdb1ff78-66ea-4848-a93e-f843a75c7f59 | 16 GB - HC | 16384 | 60 | 0 | 12 | True |
| d0e71e26-1d9e-4476-bf8b-11d32dc30483 | 16 GB - HM | 16384 | 60 | 0 | 4 | True |
| e989b4c4-4aa2-4b5c-8086-d3f407fb131f | 16 GB | 16384 | 200 | 0 | 6 | True |
| f021e071-261c-43e3-b1d7-834bc714e06b | 32 GB | 32768 | 200 | 0 | 8 | True |
+--------------------------------------+------------+-----------+------+-----------+-------+-----------+
$ openstack network list
+--------------------------------------+--------------+------------------------------------------------------+
| id | name | subnets |
+--------------------------------------+--------------+------------------------------------------------------+
| 7bc79d7b-0d04-488b-9513-b4695988840e | Demo Network | 28359fd5-5858-4ad3-94f4-673a31927603 10.200.100.0/24 |
+--------------------------------------+--------------+------------------------------------------------------+
在获取到flavor和network后就可以调用命令来创建虚拟机
$ openstack server create --flavor b5ae8e6f-03f3-4146-9add-6e84e6944ead --volume 3646ab44-e6b2-41d6-85ae-cc3dfbfb8f9a --nic net-id=7bc79d7b-0d04-488b-9513-b4695988840e boot-from-vol