Debugging Nova Command line Client

These instructions assume you have installed Nova command client in a Linux environment. If you have other operating systems, the debugging process might be a slightly different, however, the general rules should still apply.

Nova command line client is very much like other Linux commands, it outputs errors in the standard output, which is the monitor.

If you get an error, you can always read the error message and generally it give you very good hints about what might be wrong.

For example, if you execute nova service-list on the command line without authentication, the error message might look like this:

ERROR: You must provide a username via either --os-username or env[OS_USERNAME]

The above message indicates you need to be authenticated before you can use the API. The authentication requires some environment variables to be set. To set these environment variables you can either source the script file obtained from NeCTAR Dashboard or you can override it by using command line options.

You can always execute man nova or simply nova to get more help information and to learn each supported options.

If you find a useful command, you can also execute nova help command, this will give your more specific help for the command.

Debugging Nova Python API

Debugging Nova Python API takes more effects as it depends on how familiar with Python programming and what development environment you use.

The below provides some basic information about how you debug the Nova Python API.

You can debug your python code using Python debugger called pdb and you can find more information here.

The below code uses pdb debuuger to debug a python file contains clinet python API code.

pdb file_name.py

Once you executed the above code, the command line will be stopped on the first line of code and you can use some commands to control the execution flow.

Some useful ones to use are:

Debugging Via HTTP

The both of command line API and python API are restful web service client. Thus the requests are all made by using HTTP and you can always refer to OpenStack Service End for further references about what should be presented in the HTTP requests. The Nova API uses requests library to send and receive HTTP requests/responses.

For command line client, you can add --debug option to print out HTTP request header and HTTP response header, which give you a lot of more insight information. To verify parameters in the request header, you can refer to OpenStack service API to see what are expected.

To enable debugging information on the standard out for Python API, you can add the below code:

import logging
logger = logging.getLogger("novaclient")
logging.basicConfig(level=logging.DEBUG)

The will print the same output as adding --debug option for command line API.

Debugging via Source Code

If the above techniques are still not helpful, you can always look at the source code to find the problems.

The below source file structure is based on the installation in Ubuntu.

The command line nova command is located in '/usr/bin/nova'. By looking at this file, you should get a idea of how the various options are interpreted. This file acts as an interface for Python API.

The Python API files are located under '/usr/lib/python2.7/dist-packages/novaclient' and the most important file to look at is 'client.py'. This file does all the request preparation, sending request and receiving response. It is also used by the command line Nova client.