> For the complete documentation index, see [llms.txt](https://experience-digital-transform.gitbook.io/experience-digital-transformation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://experience-digital-transform.gitbook.io/experience-digital-transformation/cloud-for-dpi/chapter-3/one-request-across-several-services.md).

# One request across several services

An IaaS request crosses several independent capabilities. Identity determines who may act and in which resource boundary. The image supplies a starting operating system. Compute schedules and creates the VM. Networking creates the port, applies traffic policy and associates an external address. Block storage creates and attaches the data volume. Each capability reports its own resource state, so an `ACTIVE` VM does not prove that the volume is attached or that the floating IP points to the VM's port.[\[1\]](https://www.openstack.org/software/project-navigator/)

OpenStack implements these capabilities as projects and services:

| General capability          | OpenStack service  | Job in the request                                                        |
| --------------------------- | ------------------ | ------------------------------------------------------------------------- |
| Identity and project access | Keystone           | Authenticates an identity and scopes its permissions.                     |
| Images                      | Glance             | Supplies the approved boot image.                                         |
| Compute                     | Nova and Placement | Select capacity and create the VM.                                        |
| Networking                  | Neutron            | Creates the port, applies security groups and associates the floating IP. |
| Block storage               | Cinder             | Creates and attaches the persistent data volume.                          |
| Browser interface           | Horizon            | Presents supported service operations through a dashboard.                |

OpenStack also includes optional services for object storage, shared file systems, load balancing, DNS, secrets and orchestration. They enter a design only when the service needs those capabilities. A product catalogue is not evidence that a capability is configured or usable in a particular cloud.[\[1\]](https://www.openstack.org/software/project-navigator/)

<figure><img src="https://1406653965-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FkZFMZ3jCMUwHtTN0sL4J%2Fuploads%2Fgit-blob-eb686e368031d4f906288ac4a45ea017d886ce31%2Ffinal.png?alt=media" alt="A VM request moves from Horizon or OpenStackClient through Keystone to Glance, Nova with Placement, Neutron, and Cinder. It results in a VM, network port, floating IP and persistent volume. Each service reports the state of the resource it manages."><figcaption><p>Figure 1. The request crosses several OpenStack services, whose resource states must be read together.</p></figcaption></figure>

Video route: [C3-I1, From an IaaS request to five resource states](https://git.vanillacore.net/giga/content/src/branch/main/chapter-3/VIDEO_SCOPES.md#user-content-c3-i1-from-an-iaas-request-to-five-resource-states).


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