OpenStack REST API

There are some high quality resources that already cover the OpenStack API, so this is a YEA (yet another example) post. See the resources section below for some helpful links.

OpenStack APIs provide access to all OpenStack components, such as nova (compute), glance (VM images), swift (object storage), cinder (block storage), keystone (authentication) and neutron (networking). Authentication tokens are valid for a fixed duration, after which they expire and must be replaced. Each service requires it’s own token. Services that are hosted on the same logical server are typically accessible over different ports.

OpenStack APIs are RESTful, which means there are many ways to use them. In this post I’ll demonstrate three approaches that should provide clarity into their structure.

  • Command Line Interface (CLI)
  • cURL
  • REST Client

In this post I don’t cover programming against the REST APIs, but instead focus just on how they work. This work builds on my OpenStack development post.

Command Line Interface (CLI)

Command Line Interfaces used to manage OpenStack components make use of the REST APIs behind the scenes: a rather smart design choice on the part of the OpenStack community. This brings consistency to OpenStack management efforts and discourages disparity between standard tooling (CLI) and custom tooling (direct API access).

Credentials are required to access the REST APIs. For the command line client, these credentials are stored as environment variables. If you’re using DevStack, you can use the openrc script to automatically setup your environment.

source openrc admin admin

Some clients support a debug option that will output full details about the request and response cycle. Raw request and response details can be helpful when learning the APIs or creating programmatic access libraries that wrap the APIs. Here’s an example that will list the flavors available.

$ nova --debug flavor-list
REQ: curl -i '' -X POST -H "Accept: application/json" -H "Content-Type: application/json" -H "User-Agent: python-novaclient" -d '{"auth": {"tenantName": "admin", "passwordCredentials": {"username": "admin", "password": "{SHA1}95397c42a173838417806ce19d78f133ae6baa24"}}}'
INFO (connectionpool:258) Starting new HTTP connection (1):
DEBUG (connectionpool:375) Setting read timeout to 600.0
DEBUG (connectionpool:415) "POST HTTP/1.1" 200 6823
RESP: [200] CaseInsensitiveDict({'content-length': '6823', 'proxy-connection': 'Keep-Alive', 'vary': 'X-Auth-Token', 'server': 'Apache/2.4.7 (Ubuntu)', 'connection': 'Keep-Alive', 'date': 'Thu, 21 Aug 2014 19:09:21 GMT', 'content-type': 'application/json'})
RESP BODY: {"access": {"token": {"issued_at": "2014-08-21T19:09:21.692110", "expires": "2014-08-21T20:09:21Z", "id": "{SHA1}99ff604f28f5706bfd82a00c21e099cba7fafab2", "tenant": {"enabled": true, "description": null, "name": "admin", "id": "32c13e88d51e49179c28520f688fa74d"}}, "serviceCatalog": [{"endpoints_links": [], "endpoints": [{"adminURL": "", "region": "RegionOne", "publicURL": "", "internalURL": "", "id": "03d570ce41c04daeb7ffa274c20435f0"}], "type": "compute", "name": "nova"}, {"endpoints_links": [], "endpoints": [{"adminURL": "", "region": "RegionOne", "publicURL": "", "internalURL": "", "id": "20d2caebf4814e1bb2c05f30a4802a2c"}], "type": "volumev2", "name": "cinderv2"}, {"endpoints_links": [], "endpoints": [{"adminURL": "", "region": "RegionOne", "publicURL": "", "internalURL": "", "id": "47f43a622264422f8980f3b0fbac5f00"}], "type": "computev3", "name": "novav3"}, {"endpoints_links": [], "endpoints": [{"adminURL": "", "region": "RegionOne", "publicURL": "", "internalURL": "", "id": "149e00e61cc543cf94ae6162f79d9f00"}], "type": "s3", "name": "s3"}, {"endpoints_links": [], "endpoints": [{"adminURL": "", "region": "RegionOne", "publicURL": "", "internalURL": "", "id": "1b7a45b6d1c840978491250fd1a67204"}], "type": "image", "name": "glance"}, {"endpoints_links": [], "endpoints": [{"adminURL": "", "region": "RegionOne", "publicURL": "", "internalURL": "", "id": "0b8abc323d884a0aa657bcb2f0274ee5"}], "type": "cloudformation", "name": "heat-cfn"}, {"endpoints_links": [], "endpoints": [{"adminURL": "", "region": "RegionOne", "publicURL": "", "internalURL": "", "id": "63675bf8e9a04d199cffafb7b8354b05"}], "type": "volume", "name": "cinder"}, {"endpoints_links": [], "endpoints": [{"adminURL": "", "region": "RegionOne", "publicURL": "", "internalURL": "", "id": "520de40a96ea47c4a08c3ae5e0a8243c"}], "type": "ec2", "name": "ec2"}, {"endpoints_links": [], "endpoints": [{"adminURL": "", "region": "RegionOne", "publicURL": "", "internalURL": "", "id": "0dcff3f004ff4c9b9b96d012e47d2edb"}], "type": "orchestration", "name": "heat"}, {"endpoints_links": [], "endpoints": [{"adminURL": "", "region": "RegionOne", "publicURL": "", "internalURL": "", "id": "6f43e35702844e149dde900124c352bf"}], "type": "identity", "name": "keystone"}], "user": {"username": "admin", "roles_links": [], "id": "b9936b16c5d343588f5a19d31a55c1ea", "roles": [{"name": "_member_"}, {"name": "heat_stack_owner"}, {"name": "admin"}], "name": "admin"}, "metadata": {"is_admin": 0, "roles": ["9fe2ff9ee4384b1894a90878d3e92bab", "c28444beb7e64b4ea2ea223a6efcba6a", "3ea10423929b47779f977e11015fe480"]}}}
REQ: curl -i '' -X GET -H "Accept: application/json" -H "User-Agent: python-novaclient" -H "X-Auth-Project-Id: admin" -H "X-Auth-Token: {SHA1}99ff604f28f5706bfd82a00c21e099cba7fafab2"
INFO (connectionpool:258) Starting new HTTP connection (1):
DEBUG (connectionpool:375) Setting read timeout to 600.0
DEBUG (connectionpool:415) "GET HTTP/1.1" 200 3337
RESP: [200] CaseInsensitiveDict({'content-length': '3337', 'proxy-connection': 'Keep-Alive', 'x-compute-request-id': 'req-802ef8c9-d4a3-41e5-a93d-7ab2120089db', 'connection': 'Keep-Alive', 'date': 'Thu, 21 Aug 2014 19:09:24 GMT', 'content-type': 'application/json', 'age': '0'})
RESP BODY: {"flavors": [{"name": "m1.tiny", "links": [{"href": "", "rel": "self"}, {"href": "", "rel": "bookmark"}], "ram": 512, "OS-FLV-DISABLED:disabled": false, "vcpus": 1, "swap": "", "os-flavor-access:is_public": true, "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 0, "disk": 1, "id": "1"}, {"name": "m1.small", "links": [{"href": "", "rel": "self"}, {"href": "", "rel": "bookmark"}], "ram": 2048, "OS-FLV-DISABLED:disabled": false, "vcpus": 1, "swap": "", "os-flavor-access:is_public": true, "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 0, "disk": 20, "id": "2"}, {"name": "m1.medium", "links": [{"href": "", "rel": "self"}, {"href": "", "rel": "bookmark"}], "ram": 4096, "OS-FLV-DISABLED:disabled": false, "vcpus": 2, "swap": "", "os-flavor-access:is_public": true, "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 0, "disk": 40, "id": "3"}, {"name": "m1.large", "links": [{"href": "", "rel": "self"}, {"href": "", "rel": "bookmark"}], "ram": 8192, "OS-FLV-DISABLED:disabled": false, "vcpus": 4, "swap": "", "os-flavor-access:is_public": true, "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 0, "disk": 80, "id": "4"}, {"name": "m1.nano", "links": [{"href": "", "rel": "self"}, {"href": "", "rel": "bookmark"}], "ram": 64, "OS-FLV-DISABLED:disabled": false, "vcpus": 1, "swap": "", "os-flavor-access:is_public": true, "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 0, "disk": 0, "id": "42"}, {"name": "m1.heat", "links": [{"href": "", "rel": "self"}, {"href": "", "rel": "bookmark"}], "ram": 512, "OS-FLV-DISABLED:disabled": false, "vcpus": 1, "swap": "", "os-flavor-access:is_public": true, "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 0, "disk": 0, "id": "451"}, {"name": "m1.xlarge", "links": [{"href": "", "rel": "self"}, {"href": "", "rel": "bookmark"}], "ram": 16384, "OS-FLV-DISABLED:disabled": false, "vcpus": 8, "swap": "", "os-flavor-access:is_public": true, "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 0, "disk": 160, "id": "5"}, {"name": "m1.micro", "links": [{"href": "", "rel": "self"}, {"href": "", "rel": "bookmark"}], "ram": 128, "OS-FLV-DISABLED:disabled": false, "vcpus": 1, "swap": "", "os-flavor-access:is_public": true, "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 0, "disk": 0, "id": "84"}]}
| ID  | Name      | Memory_MB | Disk | Ephemeral | Swap_MB | VCPUs | RXTX_Factor | Is_Public |
| 1   | m1.tiny   | 512       | 1    | 0         |         | 1     | 1.0         | True      |
| 2   | m1.small  | 2048      | 20   | 0         |         | 1     | 1.0         | True      |
| 3   | m1.medium | 4096      | 40   | 0         |         | 2     | 1.0         | True      |
| 4   | m1.large  | 8192      | 80   | 0         |         | 4     | 1.0         | True      |
| 42  | m1.nano   | 64        | 0    | 0         |         | 1     | 1.0         | True      |
| 451 | m1.heat   | 512       | 0    | 0         |         | 1     | 1.0         | True      |
| 5   | m1.xlarge | 16384     | 160  | 0         |         | 8     | 1.0         | True      |
| 84  | m1.micro  | 128       | 0    | 0         |         | 1     | 1.0         | True      |

The first two sections are calls the REST APIs, first for the keystone service to Authenticate and receive a token. Responses come as JSON due to the Accept header of application/json. If you look closely, you’ll see that the response actually included an access token and entry point URLs for each of the services that are integrated with keystone. These make up the ServiceCatalog and in this case there are ten.

The second section is the actual call to the nova API. In this case it returns a list of eight flavors. The final section is a tabular view of the JSON response created by the nova command line client.


If you look closely at the debug output of the examples above, you’ll see that the command line clients use cURL to make HTTP requests. We can already see what the authentication call looks like. Calls directly to cURL look similar. For example, here I call the keystone service to get a list of tenants.

$ curl -i -X GET -H "User-Agent: linux-command-line" -H "X-Auth-Token: TOKEN"
HTTP/1.1 200 OK
Date: Thu, 21 Aug 2014 20:05:39 GMT
Server: Apache/2.4.7 (Ubuntu)
Vary: X-Auth-Token
Content-Length: 546
Content-Type: application/json
Proxy-Connection: Keep-Alive
Connection: Keep-Alive
{"tenants_links": [], "tenants": [{"description": null, "enabled": true, "id": "1b7f733fa1394b9fb96838d3d7c6feea", "name": "service"}, {"description": null, "enabled": true, "id": "298cfcec9e9e49858e9b8e83d6b7d14e", "name": "demo"}, {"description": null, "enabled": true, "id": "32c13e88d51e49179c28520f688fa74d", "name": "admin"}, {"description": null, "enabled": true, "id": "8536da0aee8149d48e1fe6078dade4bf", "name": "alt_demo"}, {"description": null, "enabled": true, "id": "e66e6a80a6014dd28c7b4c1fcad19448", "name": "invisible_to_admin"}]}

REST Client

On Windows, the tool Fiddler can be used to create REST calls. When fiddler is first started, you may need to turn off capturing of traffic. You can do this from the File menu or by pressing F12. In the right side of the window, choose the composer tab. There you can provide the URL, headers and other HTTP request details. Below you can see a call to Keystone for tokens.


The response can be viewed by selecting the resulting request in the left pane and choosing the Inspectors tab in the right pane. The results can be viewed raw, as shown here.


Fiddler also provides various parsers, including JSON, to make the content easier to visualize.



The quality of the documentation available for OpenStack APIs is really amazing. Here are a couple of starting points for you.

Twitter Digg Delicious Stumbleupon Technorati Facebook Email

About Daniel Watrous

I'm a Software & Electrical Engineer and online entrepreneur.

No comments yet... Be the first to leave a reply!

Leave a Reply