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3.7. Configure the Compute API

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.

Configure Compute API password handling

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.

Configure Compute API rate limiting

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 403 Forbidden.
Rate limiting is not available for the EC2 API.

Define limits

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.

Default limits

Normally, you install OpenStack Compute with the following limits enabled:

Table 3.5. Default API rate limits

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

Configure and change limits

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 = faultwrap authtoken keystonecontext ratelimit osapi_compute_app_v2

pipeline = faultwrap authtoken keystonecontext ratelimit osapi_volume_app_v1

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:
  1. HTTP method
  2. friendly URI
  3. regex
  4. limit
  5. interval
The following example shows the default rate-limiting values:
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)

Configuration reference

The Compute API configuration options are documented in Table 3.9, “Description of API configuration options”.