Getting "Creation of service was not idempotent" with boto3 ECS. Why?

Question

I am making a call to ecs.create_service like this:

createServiceResponse = ecs.create_service(
clientToken='abc123',
cluster=options.cluster,
serviceName=options.service,
desiredCount=1,
taskDefinition='relay:' + str(revision),
role='ecsServiceRole',
loadBalancers=[
    {
        'loadBalancerName': options.elb,
        'containerName': 'relay',
        'containerPort': 8080
    }
]
)

Note that the value in clientToken is abc123 at the moment, but I've tried all sorts of different strings. This document says I need to supply it to ensure idempotency (http://boto3.readthedocs.org/en/latest/reference/services/ecs.html) however I keep getting this error:

Traceback (most recent call last):
  File "./deploy.py", line 103, in <module>
    'containerPort': 8080
  File "/usr/local/lib/python2.7/site-packages/botocore/client.py", line 301, in _api_call
  return self._make_api_call(operation_name, kwargs)
  File "/usr/local/lib/python2.7/site-packages/botocore/client.py", line 386, in _make_api_call
   raise ClientError(parsed_response, operation_name)
botocore.exceptions.ClientError: An error occurred     (InvalidParameterException) when calling the CreateService operation: Creation of service was not idempotent.

Why ?

Answer 1

I figured it out.

It was because I was calling create_service on an existing service. I should have been calling update_service as follows:

ecs.update_service(

cluster=options.cluster,
service=options.service,
taskDefinition='relay:' + str(revision),    
desiredCount=1)