Automatically update Google Cloud DNS during Compute Engine (GCE) instance startup or shutdown

Pre-requisites

The DNS record (A) addition or deletion to/from Cloud DNS managed zone is done using a python script. The following are necessary for successful execution of the script:

• python3 and pip3 installed
• The service account attached to the GCE instance must have access to https://www.googleapis.com/auth/cloud-platform scope
• Cloud DNS with a managed zone (public / private). If you do not have a managed zone in Cloud DNS, you can set it up by following the documentation here. Here is an example:

e.g. Create a public managed zone for example.com:

> gcloud dns managed-zones create example-com \
    --dns-name="example.com" \
    --visibility=public

e.g. Create a private managed zone for example.com:

> gcloud dns managed-zones create example-com \
    --dns-name="example.com" \
    --visibility=private

• Further, each GCE instance must also have Cloud DNS project id, managed zone as well as domain name set through metadata using keys dns-project, dns-zone and dns-domain respectively. Further, you also need to set the TTL for the DNS record by passing value (in seconds) for dns-ttl key. (e.g. --metadata dns-project=abcd,dns-zone=example-com,dns-domain=example.com,dns-ttl=3600). Please refer here for more information on setting custom metadata.

Add A record during GCE instance startup and Remove A record during GCE instance shutdown

Pass the domain, startup and shutdown scripts as part of GCE instance metadata (gcloud compute instances create command)

--metadata dns-project=project-id,dns-zone=example-com,dns-domain=example.com,dns-ttl=3600,startup-script-url=gs://cloud-dns-scripts/startup.sh,shutdown-script-url=gs://cloud-dns-scripts/shutdown.sh

End to End example

Set environment variables

export DNS_PROJECT_ID=<your-dns-project-id>
export DNS_ZONE_NAME=example-com
export DNS_DOMAIN=example.com
export DNS_TTL=3600
export INSTANCE_NAME=instance-1

Create a Cloud DNS Managed Zone (private) for example.com domain with zone name as example-com

> gcloud dns managed-zones create $DNS_ZONE_NAME \
    --dns-name=$DNS_DOMAIN \
    --visibility=private

Create a GCE instance with instance name instance-1

> gcloud compute instances create $INSTANCE_NAME \
    --image=debian-9-stretch-v20191121 \
    --image-project=debian-cloud \
    --scopes=cloud-platform	\
    --metadata dns-project=$DNS_PROJECT_ID,dns-zone=$DNS_ZONE_NAME,dns-domain=$DNS_DOMAIN,dns-ttl=$DNS_TTL,startup-script-url=gs://cloud-dns-scripts/startup.sh,shutdown-script-url=gs://cloud-dns-scripts/shutdown.sh

Run the following command and check that it returns exactly one item. Also verify that the DNS record is set correctly.

> gcloud dns record-sets list --zone=$DNS_ZONE_NAME --name="$INSTANCE_NAME.$DNS_DOMAIN" --type=A

Delete the instance-1 GCE instance

> gcloud compute instances delete instance-1

Run the following command and check that it returns 0 items.

> gcloud dns record-sets list --zone=$DNS_ZONE_NAME --name="$INSTANCE_NAME.$DNS_DOMAIN" --type=A

Delete the managed DNS zone

> gcloud dns managed-zones delete $DNS_ZONE_NAME