Batfish Questions and Templates

Introduction

Questions are used to query information about a network in Batfish.

To ask a question to the Batfish service (coordinator), the client should have the template (JSON file) for that question. The question template is updated by the client with the user supplied parameters and then sent to the Batfish service in the payload for the REST API request.

So if a client is running separately from the Batfish service, corresponding template files are needed for any questions intended to be run through the client.

This directory contains the templates for two categories of questions:

1. Stable: These questions are permanent and the current plan is to support them in the future.
2. Experimental: These questions are supported currently but in the future they may be replaced/deprecated or moved to the stable directory.

Many Batfish questions use rich parameter types, the grammar for which is here.

How to run questions in Batfish Java client

Note: We recommend using Pybatfish, a powerful Python client for Batfish. The builtin Java client will deprecated soon. Pybatfish documentation has instructions and examples for loading and running questions.

Loading questions

Assumption: Batfish service (coordinator) should have been started with the path of question templates directory passed in the templatedirs parameter (see here for details)

To use a question template in the client, it needs to be loaded first. Batfish Java client provides the load-questions command to load the question templates.

To load question templates in the Java client run:

batfish> load-questions

This will load the question templates in the client and will output information about the number of questions loaded, similar to:

Loaded 191 questions
Summary: 0 (non-assertion) results;

This means that 191 questions were loaded from the Batfish service. Summary field is not relevant for this command.

Running a question

To run a question using the loaded templates, Batfish Java client provides the answer command. Run the answer command with the question name, for example:

batfish> answer ipowners

This command will run the ipOwners question on the current testrig and will fetch and print the answer on the Batfish Java client console.

Please note that answer <question-name> command treats the question-name as case-insensitive.

Loading local questions from the client

If the client wants to load its own set of questions, load-questions command can be run with the directory path containing a set of custom local question templates, for example:

batfish> load-questions ../my/local/questions

Once the local questions are loaded in the client they can also be run in the same way as the questions loaded from the Batfish service (coordinator).