Discovering the EC2 API
I've been using the EC2 API quite a lot lately, while working on the
Landscape project. The
is excellent, but I want to know how it behaves when things go wrong.
What kind of failure is produced when I forget to pass a parameter?
What happens when I pass a bogus parameter? How does it behave when I
pass numbered parameters that aren't in sequence, like
Name.7=foo&Name.42=bar? How does Amazon's implementation differ from
Eucalyptus or Nova?
I couldn't find the answers I wanted in the documentation so I wrote a
simple tool to invoke a method with an arbitrary set of parameters
against an EC2 API endpoint. After sending the request, it prints the
HTTP status code and response to the screen. It's called
txaws-discover and is part of the
txAWS project. For example, to run the
DescribeRegions method simply provide credentials, an endpoint, the
method name and whatever parameters you want to pass with it:
txaws-discover --key NUJOZS2V6RWQUJ3G8JUT \ --secret +Ki9Wk5Y4kudFh1EcnB3hthC9PtVU+CcfMJZ4DVl \ --endpoint https://ec2.us-east-1.amazonaws.com \ --action DescribeRegions \ --RegionName.0 us-west-1
This command produces the following output:
HTTP status code: 200 <DescribeRegionsResponse xmlns="http://ec2.amazonaws.com/doc/2008-12-01/"> <requestId>1e9beacc-0044-4ad6-bd2c-c615351ae46d</requestId> <regionInfo> <item> <regionName>us-west-1</regionName> <regionEndpoint>ec2.us-west-1.amazonaws.com</regionEndpoint> </item> </regionInfo> </DescribeRegionsResponse>
The credentials and API endpoint can be defined in environment
variables to make
txaws-discover easier to use:
export AWS_ACCESS_KEY_ID=NUJOZS2V6RWQUJ3G8JUT export AWS_SECRET_ACCESS_KEY=+Ki9Wk5Y4kudFh1EcnB3hthC9PtVU+CcfMJZ4DVl export AWS_ENDPOINT=https://ec2.us-east-1.amazonaws.com
With those defined, the command above can be shortened:
txaws-discover --action DescribeRegions --RegionName.0 us-west-1
It's in lp:txaws and has proven to be very helpful as a learning tool.