Builds a -i list of 1 host for running management commands

playbooks/active_instances_in_asg.py

+#!/usr/bin/env python
+
+"""
+Build an ansible inventory list suitable for use by -i by finding the active
+Auto Scaling Group in an Elastic Load Balancer.  
+
+If multiple ASGs are active in the ELB, no inventory is returned.
+
+Assuming a single active ASG is found, a single machine is returned.  This inventory
+is generally used to target a single machine in a cluster to run a cmomand.
+
+Typical reponse:
+
+10.2.42.79,
+
+Typical use
+
+ansible -i $(active_instances_in_asg.py --asg stage-edx-edxapp) -m shell -a 'management command'
+
+"""
+
+import argparse
+import botocore.session
+import botocore.exceptions
+from collections import defaultdict
+from os import environ
+
+class ActiveInventory():
+
+    profile = None
+
+    def __init__(self, profile, region):
+        self.profile = profile
+        self.region  = region
+
+    def run(self,asg_name):
+        session = botocore.session.Session(profile=self.profile)
+        asg = session.create_client('autoscaling',self.region)
+        ec2 = session.create_client('ec2',self.region)
+
+        groups = asg.describe_auto_scaling_groups()
+        matching_groups = [g for g in groups['AutoScalingGroups'] for t in g['Tags'] if t['Key'] == 'Name' and t['Value'] == asg_name]
+
+        groups_to_instances = {group['AutoScalingGroupName']: [instance['InstanceId'] for instance in group['Instances']] for group in matching_groups}
+        instances_to_groups = {instance['InstanceId']: group['AutoScalingGroupName'] for group in matching_groups for instance in group['Instances'] }
+
+        # We only need to check for ASGs in an ELB if we have more than 1.
+        # If a cluster is running with an ASG out of the ELB, then there are larger problems.
+        active_groups = defaultdict(dict)
+        if len(matching_groups) > 1:
+            elb = session.create_client('elb',self.region)
+            for group in matching_groups:
+                for load_balancer_name in group['LoadBalancerNames']:
+                    instances = elb.describe_instance_health(LoadBalancerName=load_balancer_name)
+                    active_instances = [instance['InstanceId'] for instance in instances['InstanceStates'] if instance['State'] == 'InService']
+                    for instance_id in active_instances:
+                        active_groups[instances_to_groups[instance_id]] = 1 
+            if len(active_groups) > 1:
+                # When we have more than a single active ASG, we need to bail out as we don't know what ASG to pick an instance from
+                return
+        else:
+            active_groups = { g['AutoScalingGroupName']: 1 for g in matching_groups }
+
+
+        for group in active_groups.keys():
+            for group_instance in groups_to_instances[group]:
+                instance = ec2.describe_instances(InstanceIds=[group_instance])['Reservations'][0]['Instances'][0]
+                if 'PrivateIpAddress' in instance:
+                    print "{},".format(instance['PrivateIpAddress'])
+                    return # We only want a single IP
+
+
+if __name__=="__main__":
+
+    parser = argparse.ArgumentParser()
+    parser.add_argument('-p', '--profile', help='The aws profile to use when connecting.')
+    parser.add_argument('-l', '--list', help='Ansible passes this, we ignore it.', action='store_true', default=True)
+    parser.add_argument('--asg',help='Name of the ASG we want active instances from.', required=True)
+    args = parser.parse_args()
+
+    region = environ.get('AWS_REGION','us-east-1')
+
+    ActiveInventory(args.profile,region).run(args.asg)