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Allow users to opt-out of changing instance name tags #36

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Allow users to opt-out of changing instance name tags #36

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55b82e1
Allow users to opt-out of changing instance name tags
mbillow Jul 12, 2021
e7e0553
Switch to checking a tag on the ASG to determine behavior
mbillow Aug 10, 2021
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17 changes: 17 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,17 @@ module "clever_name_autoscale_dns" {
}
```

By default, this module will also update the `Name` tag of your instance to match the short name of your pattern. If
you want to opt-out of this behavior, you can add an additional tag to your auto scaling group:

```hcl
tag {
key = "asg:update_instance_name"
value = "false"
propagate_at_launch = true
}
```

## How does it work?

The module sets up the following
Expand Down Expand Up @@ -108,6 +119,12 @@ resource "aws_autoscaling_group" "my_asg" {
value = "${var.hostname_prefix}-#instanceid.${var.vpc_name}.testing@${var.internal_zone_id}"
propagate_at_launch = true
}

# tag {
# key = "asg:update_instance_name"
# value = "false"
# propagate_at_launch = true
# }
}

module "autoscale_dns" {
Expand Down
22 changes: 15 additions & 7 deletions lambda/autoscale/autoscale.py
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@
route53 = boto3.client('route53')

HOSTNAME_TAG_NAME = "asg:hostname_pattern"
UPDATE_INSTANCE_TAG_NAME = "asg:update_instance_name"

LIFECYCLE_KEY = "LifecycleHookName"
ASG_KEY = "AutoScalingGroupName"
Expand Down Expand Up @@ -45,21 +46,25 @@ def fetch_ip_from_route53(hostname, zone_id):
return ip_address

# Fetches relevant tags from ASG
# Returns tuple of hostname_pattern, zone_id
# Returns dict of tags
def fetch_tag_metadata(asg_name):
logger.info("Fetching tags for ASG: %s", asg_name)

tag_value = autoscaling.describe_tags(
tags = autoscaling.describe_tags(
Filters=[
{'Name': 'auto-scaling-group','Values': [asg_name]},
{'Name': 'key','Values': [HOSTNAME_TAG_NAME]}
{'Name': 'key','Values': [HOSTNAME_TAG_NAME, UPDATE_INSTANCE_TAG_NAME]}
],
MaxRecords=1
)['Tags'][0]['Value']

logger.info("Found tags for ASG %s: %s", asg_name, tag_value)
tag_values = {
tag['Key']: tag['Value'] for tag in tags
}

return tag_value.split("@")
logger.info("Found tags for ASG %s: %s", asg_name, tag_values)

return tag_values

# Builds a hostname according to pattern
def build_hostname(hostname_pattern, instance_id):
Expand Down Expand Up @@ -119,13 +124,16 @@ def process_message(message):
asg_name = message['AutoScalingGroupName']
instance_id = message['EC2InstanceId']

hostname_pattern, zone_id = fetch_tag_metadata(asg_name)
asg_tag_metadata = fetch_tag_metadata(asg_name)

hostname_pattern, zone_id = asg_tag_metadata[HOSTNAME_TAG_NAME].split("@")
hostname = build_hostname(hostname_pattern, instance_id)

if operation == "UPSERT":
ip = fetch_ip_from_ec2(instance_id)

update_name_tag(instance_id, hostname)
if asg_tag_metadata.get(UPDATE_INSTANCE_TAG_NAME, "true") == "true":
update_name_tag(instance_id, hostname)
else:
ip = fetch_ip_from_route53(hostname, zone_id)

Expand Down