The Compute API, run by the nova-api daemon, is the component of
OpenStack Compute that receives and responds to user requests,
whether they be direct API calls, or via the CLI tools or
dashboard.
The OpenStack Compute API enables users to specify an administrative password when they create or rebuild a server instance. If the user does not specify a password, a random password is generated and returned in the API response.
In practice, how the admin password is handled depends on the hypervisor in use and might require additional configuration of the instance. For example, you might have to install an agent to handle the password setting. If the hypervisor and instance configuration do not support setting a password at server create time, the password that is returned by the create API call is misleading because it was ignored.
To prevent this confusion, use the
enable_instance_password
configuration option to disable the return of the admin
password for installations that do not support setting
instance passwords.
OpenStack Compute supports API rate limiting for the OpenStack API. The rate limiting allows an administrator to configure limits on the type and number of API calls that can be made in a specific time interval.
When API rate limits are exceeded, HTTP requests return
an error with a status code of 413
Request entity too large, and
includes an HTTP Retry-After header.
The response body includes the error details and the delay
before you should retry the request.
Rate limiting is not available for the EC2 API.
To define limits, set these values:
The HTTP method used in the API call, typically one of GET, PUT, POST, or DELETE.
A human readable URI that is used as a friendly description of where the limit is applied.
A regular expression. The limit is applied to all URIs that match the regular expression and HTTP method.
A limit value that specifies the maximum count of units before the limit takes effect.
An interval that specifies time frame to which the limit is applied. The interval can be SECOND, MINUTE, HOUR, or DAY.
Rate limits are applied in relative order to the HTTP method, going from least to most specific.
Normally, you install OpenStack Compute with the following limits enabled:
| HTTP method | API URI | API regular expression | Limit |
|---|---|---|---|
| POST | any URI (*) | .* | 120 per minute |
| POST | /servers | ^/servers | 120 per minute |
| PUT | any URI (*) | .* | 120 per minute |
| GET | *changes-since* | .*changes-since.* | 120 per minute |
| DELETE | any URI (*) | .* | 120 per minute |
| GET | */os-fping | ^/os-fping | 12 per minute |
As part of the WSGI pipeline, the
etc/nova/api-paste.ini file
defines the actual limits.
To enable limits, include the
ratelimit' filter in the API pipeline
specification. If the ratelimit filter is
removed from the pipeline, limiting is disabled. You must
also define the rate limit filter. The lines appear as
follows:
[pipeline:openstack_compute_api_v2] pipeline = faultwrap authtoken keystonecontext ratelimit osapi_compute_app_v2 [pipeline:openstack_volume_api_v1] pipeline = faultwrap authtoken keystonecontext ratelimit osapi_volume_app_v1 [filter:ratelimit] paste.filter_factory = nova.api.openstack.compute.limits:RateLimitingMiddleware.factory
To modify the limits, add a limits
specification to the [filter:ratelimit]
section of the file. Specify the limits in this
order:
HTTP method
friendly URI
regex
limit
interval
The following example shows the default rate-limiting values:
[filter:ratelimit] paste.filter_factory = nova.api.openstack.compute.limits:RateLimitingMiddleware.factory limits =(POST, "*", .*, 120, MINUTE);(POST, "*/servers", ^/servers, 120, MINUTE);(PUT, "*", .*, 120, MINUTE);(GET, "*changes-since*", .*changes-since.*, 120, MINUTE);(DELETE, "*", .*, 120, MINUTE);(GET, "*/os-fping", ^/os-fping, 12, MINUTE)
The Compute API configuration options are documented in Table 2.11, “Description of configuration options for api”.
