Evacuate instances

If a cloud compute node fails due to a hardware malfunction or another reason, you can evacuate instances to make them available again. You can choose evacuation parameters for your use case.

To preserve user data on server disk, you must configure shared storage on the target host. Also, you must validate that the current VM host is down; otherwise, the evacuation fails with an error.

To list hosts and find a different host for the evacuated instance, run:
```
$ nova host-list
```
Evacuate the instance. You can pass the instance password to the command by using the --password <pwd> option. If you do not specify a password, one is generated and printed after the command finishes successfully. The following command evacuates a server without shared storage from a host that is down to the specified host_b:
```
$ nova evacuate evacuated_server_name host_b 
```
The instance is booted from a new disk, but preserves its configuration including its ID, name, uid, IP address, and so on. The command returns a password:
```
+-----------+--------------+
| Property  |    Value     |
+-----------+--------------+
| adminPass | kRAJpErnT4xZ |
+-----------+--------------+
```
To preserve the user disk data on the evacuated server, deploy OpenStack Compute with a shared file system. To configure your system, see Configure migrations in OpenStack Configuration Reference. In the following example, the password remains unchanged:
```
$ nova evacuate evacuated_server_name host_b --on-shared-storage    
```

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