modified ec2 module to use EC2 idempotency via client-token attribute.

library/ec2

-#!/usr/bin/python -tt
+#!/usr/local/bin/python -tt
 # This file is part of Ansible
 #
 # Ansible is free software: you can redistribute it and/or modify
@@ -28,6 +28,12 @@ options:
     required: true
     default: null
     aliases: ['keypair']
+  id:
+    description:
+      - identifier for this instance or set of instances, so that the module will be idempotent with respect to EC2 instances.
+    required: false
+    default: null
+    aliases: []
   group:
     description:
       - security group to use with the instance
@@ -149,6 +155,7 @@ def main():
     module = AnsibleModule(
         argument_spec = dict(
             key_name = dict(required=True, aliases = ['keypair']),
+            id = dict(),
             group = dict(),
             group_id = dict(),
             instance_type = dict(aliases=['type']),
@@ -169,6 +176,7 @@ def main():
     )
 
     key_name = module.params.get('key_name')
+    id = module.params.get('id')
     group_name = module.params.get('group')
     group_id = module.params.get('group_id')
     instance_type = module.params.get('instance_type')
@@ -212,12 +220,30 @@ def main():
     except boto.exception.NoAuthHandlerFound, e:
             module.fail_json(msg = str(e))
 
+    # Lookup any instances that much our run id.
+    
+    running_instances = []
+    count_remaining = int(count)
+        
+    if id != None:
+        filter_dict = {'client-token':id, 'instance-state-name' : 'running'}
+        previous_reservations = ec2.get_all_instances(None, filter_dict )
+        for res in previous_reservations:
+            for prev_instance in res.instances:
+                running_instances.append(prev_instance)
+        count_remaining = count_remaining - len(running_instances) 
+#        module.fail_json(msg = "known running instances: %s" % (running_instances)) 
+
+    
     # Both min_count and max_count equal count parameter. This means the launch request is explicit (we want count, or fail) in how many instances we want.
 
+    
+    if count_remaining > 0:
         try:
             res = ec2.run_instances(image, key_name = key_name,
-                                min_count = count, 
-                                max_count = count,
+                                client_token=id,
+                                min_count = count_remaining, 
+                                max_count = count_remaining,
                                 monitoring_enabled = monitoring,
                                 security_groups = [group_name],
                                 instance_type = instance_type,
@@ -259,16 +285,20 @@ def main():
         if wait and wait_timeout <= time.time():
             # waiting took too long
             module.fail_json(msg = "wait for instances running timeout on %s" % time.asctime())
-    instances = []
+    
         for inst in this_res.instances:
+            running_instances.append(inst)
+        
+    instance_dict_array = []
+    for inst in running_instances:
         d = {
            'id': inst.id,
            'public_ip': inst.ip_address,
            'public_dns_name': inst.public_dns_name
             }
-        instances.append(d)
+        instance_dict_array.append(d)
 
-    module.exit_json(changed=True, instances=instances)
+    module.exit_json(changed=True, instances=instance_dict_array)
 
 # this is magic, see lib/ansible/module_common.py
 #<<INCLUDE_ANSIBLE_MODULE_COMMON>>