Initial commit

auto-update-r53.py

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+#!/usr/bin/python
+#
+# Dynamically update DNS records when the EC2 instance boots.
+# Requires boto3 installed on the instance.
+# Requries an IAM policy attached to an instance role.
+#
+
+import urllib2
+from boto3.session import Session
+import boto3
+import datetime
+
+def getRegion():
+    url = "http://169.254.169.254/2009-04-04/meta-data/placement/availability-zone"
+    try:
+        resp = urllib2.urlopen(urllib2.Request(url))
+        # Region will be a string like eu-central-1a. This chops the last character off.
+        region = resp.read()[:-1]
+    except urllib2.HTTPError as e:
+        if e.code == 404:
+            return None
+        if e.code == 500:
+            return None
+        raise
+
+    return region
+
+def getInstanceId():
+    url = "http://169.254.169.254/2009-04-04/meta-data/instance-id"
+    try:
+        resp = urllib2.urlopen(urllib2.Request(url))
+        instanceid = resp.read()
+    except urllib2.HTTPError as e:
+        if e.code == 404:
+            return None
+        if e.code == 500:
+            return None
+        raise
+
+    return instanceid
+
+def getPublicIP():
+    url = "http://169.254.169.254/2009-04-04/meta-data/public-ipv4"
+    try:
+        resp = urllib2.urlopen(urllib2.Request(url))
+        value = resp.read()
+    except urllib2.HTTPError as e:
+        if e.code == 404:
+            return None
+        if e.code == 500:
+            return None
+        raise
+
+    return value
+
+# Get region and instance ID
+myregion = getRegion()
+myinstance = getInstanceId()
+myipv4 = getPublicIP()
+
+if( myregion == None or myinstance == None or myipv4 == None):
+    print "ERROR: Could not get instance metadata. Abort."
+    exit( -1 )
+
+# Connect to EC2 and get the instance handle for this instance
+ec2 = boto3.resource('ec2', region_name=myregion)
+instance = ec2.Instance(myinstance)
+
+# Grab the tags associated with this instance
+mytags = instance.tags
+dnsname = None
+
+# Get host tag or bail
+for tag in instance.tags:
+    if( tag['Key'] == 'dnsname'):
+        dnsname = tag['Value']
+
+if (dnsname == None):
+    print "Did not find dnsname tag. "
+    exit( -1 )
+
+# Get just the domain part of dnsname
+myzone = dnsname.partition(".")[2]
+
+# Get zoneid for zone or bail
+session = Session(region_name=myregion)
+client = session.client('route53')
+# Note: if you have more than 100 hosted zones, there's a chance that
+# the zone you need won't be returned in response to the first call
+# to list_hosted_zones(). The next loop will fail to find your zone.
+#
+# If this applies to you, you have to rewrite this section to use
+# pagination to iterate over the collection of returned domains,
+# looking for the one you want. That extension is left as an
+# exercise for the reader.
+myzoneid = None
+zones = client.list_hosted_zones()
+
+# Route53 will return zones in canonical form with the trailing dot.
+# e.g.: "ec2.example.com."
+# It's likely that people will enter dnsnames in the tags without the
+# trailing dot, so this helps make the match either way.
+for zone in zones['HostedZones']:
+    if( (zone['Name'] == myzone) or (zone['Name'] == myzone + ".")):
+        myzoneid = zone['Id']
+
+if( myzoneid == '' ):
+    # didn't find the zone
+    print "ERROR: Did not find " + myzone + " among the hosted zones."
+    exit( -1 )
+
+# Create record set update
+print "setting " + dnsname + " to " + myipv4
+now = datetime.datetime.now()
+
+response = client.change_resource_record_sets(
+    HostedZoneId=myzoneid,
+    ChangeBatch={
+        'Comment': 'Instance ' + myinstance + ' boot at ' + now.strftime("%Y-%m-%d %H:%M"),
+        'Changes': [
+            {
+                'Action': 'UPSERT',
+                'ResourceRecordSet': {
+                    'TTL': 300,
+                    'Name': dnsname,
+                    'Type': 'A',
+                    'ResourceRecords': [
+                        {
+                            'Value': myipv4
+                        },
+                    ]
+                }
+            },
+        ]
+    }
+)
+
+# Check for error.
+if( response['ResponseMetadata']['HTTPStatusCode'] != 200 ):
+    print "ERROR updating Route53"
+    print response
+    exit( -1 )

dns-update-policy.json

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+{
+    "Version": "2012-10-17",
+    "Statement": [
+        {
+            "Action": [
+                "route53:ChangeResourceRecordSets",
+                "route53:GetHostedZone",
+                "route53:ListResourceRecordSets"
+            ],
+            "Effect": "Allow",
+            "Resource": [
+                "arn:aws:route53:::hostedzone/[ZONEID]",
+            ]
+        },
+        {
+            "Action": [
+                "route53:ListHostedZones",
+                "ec2:DescribeInstances"
+            ],
+            "Effect": "Allow",
+            "Resource": [
+                "*"
+            ]
+        }
+    ]
+}