openstack server resize

OpenStack Server Resize

1. Introduction

OpenStack is an open-source cloud computing platform that allows users to deploy and manage virtual machines and other resources. One of the key features of OpenStack is the ability to resize servers, which enables users to change the flavor (an instance type that determines the virtual hardware resources) of a running server without stopping or rebooting it.

In this article, we will explore the process of resizing an OpenStack server using the OpenStack Python SDK. We will cover the steps involved in resizing a server and provide code examples along the way. Additionally, we will create a flowchart to visualize the resizing process and a class diagram to illustrate the relevant classes and their relationships.

2. Resizing an OpenStack Server

Resizing an OpenStack server involves the following steps:

Step 1: Authenticate with OpenStack

Before interacting with the OpenStack API, we need to authenticate ourselves using our credentials. This can be done using the "keystoneauth1" library, which provides authentication plugins for different authentication methods. Here is an example of authenticating with OpenStack using the "password" authentication method:

from keystoneauth1 import loading, session

# Create an authentication plugin
loader = loading.get_plugin_loader('password')
auth = loader.load_from_options(auth_url='http://<keystone-url>/v3',
                                username='<username>',
                                password='<password>',
                                project_name='<project-name>',
                                user_domain_name='<user-domain-name>',
                                project_domain_name='<project-domain-name>')

# Create a session using the authentication plugin
sess = session.Session(auth=auth)

Step 2: Retrieve the Server

Next, we need to retrieve the server that we want to resize. We can use the "nova" client from the OpenStack SDK to query the server by its ID:

from novaclient import client

# Create a nova client
nova = client.Client('2.1', session=sess)

# Retrieve the server by ID
server = nova.servers.get('<server-id>')

Step 3: Check Resize Eligibility

Before resizing a server, it's important to check if the server meets the requirements for resizing. This includes verifying if the server is in a running state and if the desired flavor is available. We can use the "nova" client to perform these checks:

# Check if the server is in a running state
if server.status != 'ACTIVE':
    raise Exception('Server must be in the "ACTIVE" state.')

# Check if the desired flavor is available
available_flavors = nova.flavors.list()
desired_flavor = 'm2.medium'  # Replace with the desired flavor name

if desired_flavor not in [flavor.name for flavor in available_flavors]:
    raise Exception('Desired flavor is not available.')

Step 4: Resize the Server

Once we have verified the eligibility, we can proceed with resizing the server. We need to call the resize method on the server instance and provide the ID or name of the desired flavor. Here is an example of resizing a server:

# Resize the server
server.resize(desired_flavor)

Step 5: Confirm the Resize

After initiating the resize, we need to confirm the resize operation to apply the changes. This can be done using the confirm_resize method on the server instance:

# Confirm the resize
server.confirm_resize()

Step 6: Verify the Resized Server

Finally, we should verify that the server has been successfully resized. We can check the server's flavor to ensure it matches our desired flavor:

# Refresh the server object to get the updated flavor
server = nova.servers.get(server.id)

# Check if the server's flavor has been updated
if server.flavor['name'] != desired_flavor:
    raise Exception('Server resize failed.')

3. Flowchart

flowchart TD
    A[Authenticate with OpenStack] --> B[Retrieve the Server]
    B --> C[Check Resize Eligibility]
    C --> D[Resize the Server]
    D --> E[Confirm the Resize]
    E --> F[Verify the Resized Server]

4. Class Diagram

classDiagram
    class OpenStackServer {
        +server_id : str
        +nova : novaclient.Client

        +__init__(server_id: str)
        +get_server() : novaclient.v2.servers.Server
        +check_eligibility() : bool
        +resize(flavor: str) : None
        +confirm_resize() : None
        +verify_resized() : None
    }

    class NovaClient {
        +sess : keystoneauth1.session.Session

        +__init__(sess: keystoneauth1.session.Session)
        +flavors : novaclient.base.ListExtension
        +servers : novaclient.base.ListExtension
        +flavors_list() : List[Flavor]
        +servers_get(server_id: str) : novaclient.v2.servers.Server
    }

    class Flavor {
        +name : str
    }

    OpenStackServer --> NovaClient
    NovaClient --> Flavor

5. Conclusion

In this article