The design document for the API can be found below. This document contains the API as of the current release:


There are two top-level concepts in today’s API: Policies and Data-sources.

  • Policies have rules that describe the permitted states of the cloud, along with tables representing abstractions of the cloud state.
  • Data-sources have tables representing the current state of the cloud.
  • The tables of both policies and data-sources have rows that describe their contents.

1. Policy (/v1/)

You can create and delete policies. Two policies are provided by the system, and you are not permitted to delete them: classification and action. A policy has the following fields:

  • name: a unique name that is human-readable

  • abbreviation: a shorter name that appears in traces

  • description: an explanation of this policy’s purpose

  • kind: kind of policy. Supported kinds are -
    1. nonrecursive,
    2. action,
    3. database,
    4. materialized

    The default is nonrecursive and unless you are writing action descriptions for use with simulate you should always use the default.

Op URL Result
GET …/policies List policies
GET …/policies/<policy-id> Read policy properties
POST …/policies Create new policy
POST …/policies/<policy-id> Policy action (simulate)
DELETE …/policies/<policy-id> Delete policy

Create new policy

Create new policy with empty rule set

This operation creates a new policy with an empty rule set, presumably to be populated later with rules.


POST: .../policies with the following request body:

  "name": "policy_name_1"

Create new policy from policy library

This operation activates a policy from the policy library.

Specify the the name of the library policy library_policy parameter.


POST: .../policies?library_policy=DisallowedServerImages with empty request body.

Create new policy with rules

This operation creates a new policy along with the specified policy rules.


POST: .../policies with the following request body:

  "name": "policy_name_2",
  "rules": [
    {"rule": "multiple_ip(port_id) :- port(port_id, ip1), port(port_id, ip2), not equal(ip1, ip2)",
     "comment": "ports with multiple IP addresses"},
    {"rule": "single_id(port_id) :- port(port_id, ip), not multiple_ip(port_id)"}

Policy action

You can utilize the simulation API call, which answers hypothetical questions: if we were to change the state of the cloud in this way, what would the answer to this query be? See Monitoring and Enforcement for more details and examples:

POST .../policies/<policy-id>
  [&delta=true]                    # return just change in <query>
  [&trace=true]                    # also return explanation of result

Request Body
  "query" : "<query>",                 # string query like: 'error(x)'
  "sequence": "<sequence>",            # changes to state like: 'p+(1) p-(2)'
  "action_policy" : "<action_policy>"  # name of a policy: 'action'

2. Policy Rules (/v1/policies/<policy-id>/…)

Each policy is a collection of rules. Congress supports the usual CRUD operations for changing that collection. A rule has the following fields:

  • ID: a unique identifier
  • name: a human-friendly identifier
  • rule: a string representing the actual rule as described in Policy
  • comment: description or comment related to the rule
Op URL Result
GET …/rules List policy rules
POST …/rules Create policy rule
GET …/rules/<rule-id> Read policy rule
DELETE …/rules/<rule-id> Delete policy rule

3. Policy Tables (/v1/policies/<policy-id>/…)

All the tables mentioned in the rules of a policy can be queried via the API. They have only an ID field.

Op URL Result
GET …/tables List tables
GET …/tables/<table-id> Read table properties

4. Policy Table Rows (/v1/policies/<policy-id>/tables/<table-id>/…)

Rules are used to instruct Congress how to create new tables from existing tables. Congress allows you to query the actual contents of tables at any point in time. Congress will also provide a trace of how it computed a table, to help policy authors understand why certain rows belong to the table and others do not.

Op URL Result
GET …/rows List rows
GET …/rows?trace=true List rows with explanation (use ‘printf’ to display)

5. Drivers (/v1/system/)

A driver is a piece of code that once instantiated and configured interacts with a specific cloud service like Nova or Neutron. A driver has the following fields.

  • ID: a human-friendly unique identifier
  • description: an explanation of which type of cloud service this driver interacts with
Op URL Result
GET …/drivers List drivers
GET …/drivers/<driver-id> Read driver properties

Drivers were deprecated in Liberty, but the design changed slightly so that we could retain them.

6. Data sources (/v1/)

A data source is an instantiated and configured driver that interacts with a particular instance of a cloud service (like Nova or Neutron). You can construct multiple datasources using the same driver. For example, if you have two instances of Neutron running, one in production and one in test and you want to write policy over both of them, you would create two datasources using the Neutron driver and give them different names and configuration options. For example, you might call one datasource ‘neutron_prod’ and the other ‘neutron_test’ and configure them with different IP addresses.

A datasource has the following fields.

  • ID: a unique identifier
  • name: a human-friendly unique that is unique across datasources and policies
  • driver: the name of the driver code that this datasource is running
  • config: a dictionary capturing the configuration of this datasource
  • description: an explanation of the purpose of this datasource
  • enabled: whether or not this datasource is functioning (which is always True)
Op URL Result
GET …/data-sources List data sources
POST …/data-sources Create data source
DELETE …/data-sources/<ds-id> Delete data source
GET …/data-sources/<ds-id>/schema Show schema (tables and table-columns)
GET …/data-sources/<ds-id>/status Show data source status
GET …/data-sources/<ds-id>/actions List supported data source actions

7. Data source Tables (/v1/data-sources/<ds-id>/…)

Each data source maintains a collection of tables (very similar to a Policy). The list of available tables for each data source is available via the API. A table just has an ID field.

Op URL Result
GET …/tables List data sources
GET …/tables/<table-id> Read data source properties
GET …/tables/<table-id>/spec Show a table schema

8. Data source Table Rows (/v1/data-sources/<ds-id>/tables/<table-id>/…)

The contents of each data source table (the rows of each table) can be queried via the API as well. A row has just a Data field, which is a list of values.

Op URL Result
GET …/rows List rows

9. Versions (/)

You can see the supported API versions.

Op URL Result
GET …/ List supported versions
GET …/<version-id> Read version
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