API validation using jsonschema


Currently, Blazar has different implementations for validating request bodies. The purpose of this blueprint is to validate the request body in the API layer using json schema validation before it is forwarded to any of the other Blazar components. Validating the request bodies sent to the Blazar server, accepting requests that fit the resource schema and rejecting requests that do not fit the schema. Depending on the content of the request body, the request should be accepted or rejected.

Problem description

Currently Blazar doesn’t have a consistent request validation layer. Some resources validate input at the resource controller and some fail out in the backend. Ideally, Blazar would have some validation in place to catch disallowed parameters and return a validation error to the user.

The end user will benefit from having consistent and helpful feedback, regardless of which resource they are interacting with.

Use Cases

As a user or developer, I want to observe consistent API validation and values passed to the Blazar API server.

Proposed change

One possible way to validate the Blazar API is to use jsonschema similar to Nova, Keystone and Glance (https://pypi.python.org/pypi/jsonschema). A jsonschema validator object can be used to check each resource against an appropriate schema for that resource. If the validation passes, the request can follow the existing flow of control through the resource manager to the backend. If the request body parameters fails the validation specified by the resource schema, a validation error wrapped in HTTPBadRequest will be returned from the server.


Before the API validation framework, we needed to add the validation code into each API method in ad-hoc. These changes would make the API method code dirty and we need to create multiple patches due to incomplete validation.

If using JSON Schema definitions instead, acceptable request formats are clear and we don’t need to do ad-hoc works in the future.

Data model impact


REST API impact

API Response code changes:

There are some occurrences where API response code will change while adding schema layer for them. For example, On current master ‘computehosts’ table has ‘hypervisor_hostname’ of maximum 255 characters in database table. While creating host user can pass ‘host’ of more than 255 characters which obviously fails with 404 HostNotFound wasting a database call. For this we can restrict the ‘host’ of maximum 255 characters only in schema definition of ‘os-hosts’. If user passes more than 255 characters, he/she will get 400 BadRequest in response.

API Response error messages:

There will be change in the error message returned to user. For example, On current master if user passes nothing for host name like “name”: “” then below error message is returned to user from blazar-api:

“Host ‘’ not found!”.

With schema validation below error message will be returned to user for this case:

Invalid input for field/attribute name. Value: <value passed by user>. ‘<value passed by user>’ is too short.

Security impact

The output from the request validation layer should not compromise data or expose private data to an external user. Request validation should not return information upon successful validation. In the event a request body is not valid, the validation layer should return the invalid values and/or the values required by the request, of which the end user should know. The parameters of the resources being validated are public information, described in the Blazar API reference document with the exception of private data. In the event the user’s private data fails validation, a check can be built into the error handling of the validator not to return the actual value of the private data.

Jsonschema documentation notes security considerations for both schemas and instances.

Better up front input validation will reduce the ability for malicious user input to exploit security bugs.

Notifications impact


Other end user impact


Performance Impact

Blazar will need some performance cost for this comprehensive request parameters validation, because the checks will be increased for API parameters which are not validated now.

Other deployer impact


Developer impact

This will require developers contributing new extensions to Blazar to have a proper schema representing the extension’s API.



Primary assignee: Asmita Singh : <asmita.singh@nttdata.com>

Work Items

  1. Initial validator implementation, which will contain common validator code designed to be shared across all resource controllers validating request bodies.

  2. Introduce validation schemas for existing API resources.

  3. Enforce validation on proposed API additions and extensions.

  4. Remove duplicated ad-hoc validation code.

  5. Add unit and end-to-end tests of related APIs.

  6. Add/Update Blazar documentation.




Some tests can be added as each resource is validated against its schema. These tests should walk through invalid request types.

Documentation Impact

  1. The Blazar API documentation will need to be updated to reflect the REST API changes.

  2. The Blazar developer documentation will need to be updated to explain how the schema validation will work and how to add json schema for new APIs.


Some useful links:



Release Name