Collect Custom DNS logs

Supported in:

Google secops SIEM

This document explains how to ingest Custom DNS logs to Google Security Operations using Google Cloud Storage V2.

Custom DNS is a generic log type for DNS server logs from custom or unsupported DNS implementations. It captures DNS query and response data including domains, record types, and client information. Because these logs come from non-standard DNS sources, you must export them to a Google Cloud Storage (GCS) bucket, and then configure a Google SecOps feed to ingest them.

Before you begin

Make sure you have the following prerequisites:

• A Google SecOps instance
• A Google Cloud project with Cloud Storage API enabled
• Permissions to create and manage GCS buckets
• Permissions to manage IAM policies on GCS buckets
• A DNS server or service generating logs in a supported format (JSON recommended)
• Administrative access to the DNS server to configure log exports

Create a Google Cloud Storage bucket

1. Go to the Google Cloud Console.
2. Select your project or create a new one.
3. In the navigation menu, go to Cloud Storage > Buckets.
4. Click Create bucket.

5. Provide the following configuration details:

   Setting	Value
   Name your bucket	Enter a globally unique name (for example, custom-dns-logs)
   Location type	Choose based on your needs (Region, Dual-region, Multi-region)
   Location	Select the location closest to your Google SecOps instance (for example, us-central1)
   Storage class	Standard (recommended for frequently accessed logs)
   Access control	Uniform (recommended)
   Protection tools	Optional: Enable object versioning or retention policy

6. Click Create.

   Note: Record the bucket name. You will use it when configuring the Google SecOps feed.

Configure an automated export of DNS logs to GCS

The method for exporting DNS logs depends on your DNS server implementation. Choose the approach that best matches your environment.

Option 1: Cloud Logging sink (for DNS servers on GCE)

If your DNS server runs on a Google Compute Engine instance and logs to Cloud Logging, create a log sink to export DNS logs directly to GCS.

1. In the GCP Console, go to Logging > Log Router.
2. Click Create Sink.

3. Provide the following configuration details:

   Setting	Value
   Sink name	custom-dns-to-gcs
   Sink destination	Cloud Storage bucket
   Bucket	custom-dns-logs
   Inclusion filter	A filter matching your DNS log entries (for example, resource.type="gce_instance" AND logName="projects/YOUR_PROJECT_ID/logs/dns")

4. Click Create Sink.

   Note: The log sink automatically writes matching log entries to the GCS bucket as JSON files. No additional scheduling is needed.

Option 2: Cloud Scheduler with Cloud Build (for on-premises DNS servers)

Use Cloud Build triggered by Cloud Scheduler to run a containerized export job that collects DNS logs from a remote server and writes them to GCS.

1. Create a service account for the export job:

   1. In the GCP Console, go to IAM & Admin > Service Accounts.
   2. Click Create Service Account.
   3. Provide the following configuration details:
      • Service account name: Enter dns-log-export-sa
      • Service account description: Enter Service account for automated DNS log export to GCS
   4. Click Create and Continue.
   5. Add the following roles:
      • Storage Object Admin (to write files to GCS)
      • Cloud Build Editor (to run Cloud Build jobs)
   6. Click Done.

2. Create a Cloud Build configuration file (cloudbuild.yaml):

   steps:
     - name: 'gcr.io/cloud-builders/gcloud'
       entrypoint: 'bash'
       args:
         - '-c'
         - |
           # Collect DNS logs from your server
           # Replace with the actual command for your environment
           # Example: pull logs via syslog-ng, rsync from remote server, or query DNS log API
           curl -s -H "Authorization: Bearer $${API_TOKEN}" \
             "https://your-dns-server.example.com/api/logs?format=json" \
             -o /workspace/dns_logs.json
           # Upload to GCS
           gcloud storage cp /workspace/dns_logs.json \
             gs://${_BUCKET_NAME}/dns/dns_logs_$(date -u +%Y%m%d_%H%M%S).json
   substitutions:
     _BUCKET_NAME: 'custom-dns-logs'
   

   Note: Replace the curl command with the actual command for your DNS server. For example, use scp to copy log files from a remote server, or use an API call to query a DNS management platform.

3. Create a Cloud Scheduler job to trigger the build:

   1. In the GCP Console, go to Cloud Scheduler.
   2. Click Create Job.

   3. Provide the following configuration details:

      Setting	Value
      Name	dns-log-export-hourly
      Region	Select the same region as your GCS bucket
      Frequency	0 * * * * (every hour)
      Timezone	UTC (recommended)
      Target type	HTTP
      URL	https://cloudbuild.googleapis.com/v1/projects/YOUR_PROJECT_ID/builds
      HTTP method	POST
      Auth header	Add OAuth token
      Service account	dns-log-export-sa@YOUR_PROJECT_ID.iam.gserviceaccount.com

   4. Click Create.

Option 3: Storage Transfer Service (for on-premises file systems)

If DNS logs are written to a local file system, use Storage Transfer Service with a Transfer Agent to move them to GCS.

1. In the GCP Console, go to Storage Transfer Service.
2. Click Create transfer job.
3. Select POSIX filesystem as the source.
4. Follow the instructions to install the Storage Transfer Agent on the DNS server or a machine with access to the DNS log files.

5. Configure the transfer job:

   Setting	Value
   Source directory	Path to the DNS log file directory
   Destination bucket	custom-dns-logs
   Destination path	dns/
   Schedule	Set a recurring schedule (for example, every hour)

6. Click Create.

Retrieve the Google SecOps service account

1. Go to SIEM Settings > Feeds.
2. Click Add New Feed.
3. Click Configure a single feed.
4. In the Feed name field, enter a name for the feed (for example, Custom DNS Logs).
5. Select Google Cloud Storage V2 as the Source type.
6. Select Custom DNS as the Log type.
7. Click Get Service Account.

8. A unique service account email will be displayed, for example:

   [e-mail]
   

9. Copy this email address for use in the next step.

   Note: Each Google SecOps instance has a unique service account. Do not use service accounts from other documentation or examples.

Grant IAM permissions to the Google SecOps service account

The Google SecOps service account needs Storage Object Viewer role on your GCS bucket.

1. Go to Cloud Storage > Buckets.
2. Click on your bucket name (for example, custom-dns-logs).
3. Go to the Permissions tab.
4. Click Grant access.
5. Provide the following configuration details:
   • Add principals: Paste the Google SecOps service account email (for example, [e-mail]).
   • Assign roles: Select Storage Object Viewer.

6. Click Save.

   Note: If you plan to use the deletion option "Delete transferred files" or "Delete transferred files and empty directories," grant Storage Object Admin role instead of Storage Object Viewer.

Configure the Google SecOps feed

1. Go to SIEM Settings > Feeds.
2. Click Add New Feed.
3. Click Configure a single feed.
4. In the Feed name field, enter a name for the feed (for example, Custom DNS Logs).
5. Select Google Cloud Storage V2 as the Source type.
6. Select Custom DNS as the Log type.
7. Click Next.

8. Specify values for the following input parameters:

   • Storage bucket URI: Enter the GCS bucket URI:

     gs://custom-dns-logs/dns/
     

     • Replace custom-dns-logs with your GCS bucket name.
     • Replace dns with your configured prefix path.
   Note: Always include the trailing slash (/) at the end of the URI.

   • Source deletion option: Select the deletion option according to your preference:

     • Never: Never deletes any files after transfers (recommended for testing).

     • Delete transferred files and empty directories: Deletes files and empty directories after successful transfer.

       Note: If you select a deletion option, the Google SecOps service account must have Storage Object Admin role instead of Storage Object Viewer. Update IAM permissions accordingly.

   • Maximum File Age: Include files modified in the last number of days (default is 180 days).

   • Asset namespace: The asset namespace.

   • Ingestion labels: The label to be applied to the events from this feed.

9. Click Next.

10. Review your new feed configuration in the Finalize screen, and then click Submit.

UDM mapping table

Log Field	UDM Mapping	Logic
receiveTimestamp	metadata.event_timestamp	Parsed as RFC3339
message	metadata.event_type	Mapped: "dns_query" → NETWORK_DNS
jsonPayload.msg	metadata.product_event_type	Directly mapped
insertId	metadata.product_log_id	Directly mapped
message	metadata.product_name	Mapped: "dns_query" → Custom DNS
message	metadata.vendor_name	Mapped: "dns_query" → CUSTOM
message	network.application_protocol	Mapped: "dns_query" → DNS
dns_answers	network.dns.answers	Merged
message	network.dns.answers	Mapped: "dns_query" → dns_answers
dns_question	network.dns.questions	Merged
message	network.dns.questions	Mapped: "dns_query" → dns_question
dns.response_code	network.dns.response_code	Renamed/mapped
message	principal.hostname	Mapped: "dns_query" → jsonPayload.dns_query.server
jsonPayload.dns_query.server	principal.ip	Merged
message	principal.ip	Mapped: "dns_query" → jsonPayload.dns_query.server
message	security_result	Mapped: "dns_query" → security_result
logName	security_result.category_details	Merged
message	security_result.category_details	Mapped: "dns_query" → logName
message	security_result.severity	Mapped: "dns_query" → INFORMATIONAL, "dns_query" → MEDIUM, "dns_query" → HIGH
labels.application	target.application	Directly mapped
message	target.hostname	Mapped: "dns_query" → jsonPayload.dns_query.server
jsonPayload.dns_query.server	target.ip	Merged
message	target.ip	Mapped: "dns_query" → jsonPayload.dns_query.server
component_label	target.labels	Merged
instance_group_label	target.labels	Merged
message	target.labels	Mapped: "dns_query" → component_label, "dns_query" → instance_group_label
labels.region	target.location.country_or_region	Directly mapped
resource.labels.zone	target.resource.attribute.cloud.availability_zone	Directly mapped
message	target.resource.attribute.cloud.environment	Mapped: "dns_query" → GOOGLE_CLOUD_PLATFORM
resource.labels.project_id	target.resource.attribute.cloud.project.id	Directly mapped
message	target.resource.resource_type	Mapped: "dns_query" → VIRTUAL_MACHINE
N/A	metadata.event_type	Constant: NETWORK_DNS
N/A	metadata.product_name	Constant: Custom DNS
N/A	metadata.vendor_name	Constant: CUSTOM
N/A	network.application_protocol	Constant: DNS
N/A	principal.hostname	Constant: jsonPayload.dns_query.server
N/A	security_result.severity	Constant: INFORMATIONAL
N/A	target.hostname	Constant: jsonPayload.dns_query.server
N/A	target.resource.attribute.cloud.environment	Constant: GOOGLE_CLOUD_PLATFORM
N/A	target.resource.resource_type	Constant: VIRTUAL_MACHINE

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