Mastering the 'nova' Command in OpenStack (with examples)

The ’nova’ command is a powerful tool in the OpenStack ecosystem that allows users to manage and provision compute resources effectively. It provides the ability to list, boot, start, and stop virtual machines (VMs) or compute instances, as well as attach network interfaces to them. This makes it an essential utility for cloud administrators and users alike who are tasked with deploying and managing cloud-based environments.

Use case 1: List VMs on Current Tenant

Code:

nova list

Motivation:

This command is essential for users who want to view all active virtual machines or compute instances within their current OpenStack tenant. Listing VMs helps in quickly assessing resource utilization, monitoring the status of instances, and performing further operations like management or troubleshooting.

Explanation:

• nova: The command-line tool for interacting with the OpenStack compute service.
• list: This subcommand is used to display a list of all VMs currently running within the user’s tenant.

Example Output:

+--------------------------------------+----------+---------+------------+-------------+------------------+
| ID                                   | Name     | Status  | Task State | Power State | Networks         |
+--------------------------------------+----------+---------+------------+-------------+------------------+
| 12345678-abcd-efgh-ijkl-1234567890ab | example1 | ACTIVE  | -          | Running     | private=192.168.1.5 |
| 23456789-bcde-fghi-jklm-234567890bcd | example2 | SHUTOFF | -          | Shutdown    | private=192.168.1.8 |
+--------------------------------------+----------+---------+------------+-------------+------------------+

Use case 2: List VMs of All Tenants (Admin User Only)

Code:

nova list --all-tenants

Motivation:

For cloud administrators, having an oversight across all tenants’ VMs can be crucial for resource management, billing, and auditing purposes. By being able to list VMs across all tenants, administrators can ensure fair resource distribution and identify any anomalies or potential issues in different cloud environments.

Explanation:

• nova: The command-line tool for managing compute instances.
• list: Displays a list of all VMs.
• --all-tenants: This flag ensures that the list includes VMs from all tenants, not just the current one. This requires administrative privileges.

Example Output:

+--------------------------------------+------------+---------+------------+-------------+-----------------------+
| ID                                   | Name       | Status  | Task State | Power State | Networks              |
+--------------------------------------+------------+---------+------------+-------------+-----------------------+
| 34567890-cdef-ghij-klmn-34567890cdef | admin-vm1  | ACTIVE  | -          | Running     | admin-net=10.0.0.5    |
| 45678901-defg-hijk-lmno-45678901defg | tenant2-vm | SHUTOFF | -          | Shutdown    | tenant2-net=10.0.1.8  |
+--------------------------------------+------------+---------+------------+-------------+-----------------------+

Use case 3: Boot a VM on a Specific Host

Code:

nova boot --nic net-id=net_id --image image_id --flavor flavor --availability-zone nova:host_name vm_name

Motivation:

Booting a VM on a specific host is useful for ensuring that resources are allocated on preferred physical hosts. This can be instrumental in adherence to organizational policies, optimizing for performance, or ensuring proximity to specific resources or services for reduced latency.

Explanation:

• nova: Command tool for OpenStack compute service operations.
• boot: Subcommand to create and start a new VM instance.
• --nic net-id=net_id: Specifies the network ID to which the VM’s network interface should connect.
• --image image_id: Indicates the image ID that will be used for the instance’s root volume.
• --flavor flavor: Determines the instance’s hardware configuration, such as the amount of RAM and CPU.
• --availability-zone nova:host_name: Specifies the availability zone and the specific host where the VM should be launched.
• vm_name: The desired name of the new VM.

Example Output:

+-------------------------+--------------------------------------+
| Property                | Value                                |
+-------------------------+--------------------------------------+
| OS-EXT-AZ:availability_zone | nova:host_name                   |
| flavor                  | m1.small                             |
| id                      | 56789012-ghij-klmn-opqr-56789012ghij |
| image                   | cirros-0.4.0-x86_64-disk             |
| name                    | my_vm                                |
| status                  | BUILD                                |
+-------------------------+--------------------------------------+

Use case 4: Start a Server

Code:

nova start server

Motivation:

Starting a server is a fundamental function when performing maintenance operations or optimizing resource usage. Servers might be stopped for updates, energy savings, or addressing resource conflicts, and knowing how to start them ensures restored access to critical applications and services.

Explanation:

• nova: The OpenStack compute service command-line tool.
• start: Subcommand used to transition the specified server from a stopped state to a running state.
• server: The identifier (ID or name) of the server to be started.

Example Output:

Request to start server has been accepted.

Use case 5: Stop a Server

Code:

nova stop server

Motivation:

Stopping a server is often necessary during scheduled maintenance, when rectifying system issues, or when a server is no longer needed temporarily. This command effectively halts operations to save resources or prepare the server for a different set of tasks.

Explanation:

• nova: The command-line tool to manage OpenStack compute instances.
• stop: Subcommand used to transition a server from a running state to a stopped state.
• server: The identifier (ID or name) of the server to be stopped.

Example Output:

Request to stop server has been accepted.

Use case 6: Attach a Network Interface to a Specific VM

Code:

nova interface-attach --net-id net_id server

Motivation:

Attaching a network interface to a VM is critical when you need to expand its connectivity, provide access to additional network resources, or reconfigure its network settings. This capability allows for dynamic adjustments to meet evolving network demands without recreating or significantly altering the existing VM setup.

Explanation:

• nova: The command-line interface for OpenStack compute services.
• interface-attach: Subcommand to attach a new network interface to an existing VM.
• --net-id net_id: Specifies the network ID to which the network interface should be attached.
• server: The identifier (ID or name) of the VM to which the network interface will be added.

Example Output:

+-------------------+--------------------------------------+
| Property          | Value                                |
+-------------------+--------------------------------------+
| net_id            | net_id_value                         |
| port_id           | 89012345-ijkl-mnop-qrst-89012345ijkl |
| fixed_ips         | 10.0.0.25                            |
| mac_address       | fa:16:3e:2e:5e:55                    |
| port_state        | ACTIVE                               |
+-------------------+--------------------------------------+

Conclusion

The ’nova’ command in OpenStack serves as a comprehensive toolset for cloud administrators and users to manage compute instances effectively. From listing VMs to booting them on specific hosts and managing their network interfaces, the command covers a vast range of functionalities necessary for efficient cloud operations. Understanding these use cases and employing them effectively can significantly enhance resource management and operational efficiency in any OpenStack deployment.