Ensure GCP VPC flow logs for the subnet is set to On

Error: GCP VPC flow logs for the subnet is set to Off

Bridgecrew Policy ID: BC_GCP_LOGGING_1
Checkov Check ID: CKV_GCP_26
Severity: MEDIUM

GCP VPC flow logs for the subnet is set to Off


Flow Logs capture information about IP traffic going to and from network interfaces. This information can be used to detect anomalous traffic and insight about security workflows. You can view and retrieve flow log data in Stackdriver Logging.

VPC networks and subnetworks provide logically isolated and secure network partitions to launch Google Cloud Platform (GCP) resources. When Flow Logs are enabled for a subnet, VMs within that subnet report on all Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) flows. Each VM samples the inbound and outbound TCP and UDP flows it sees, whether the flow is to or from another VM, a host in the on-premises datacenter, a Google service, or a host on the Internet. If two GCP VMs are communicating and both are in subnets that have VPC Flow Logs enabled, both VMs report the flows.

We recommended you set Flow Logs to On to capture this data. Because the volume of logs may be high, you may wish to enable flow logs only for business-critical VPC Network Subnets.

Flow Logs supports the following use cases:

  • Network monitoring
  • Understanding network usage and optimizing network traffic expenses
  • Network forensics
  • Real-time security analysis

Fix - Runtime

GCP Console

  1. Open the VPC network GCP Console https://console.cloud.google.com/networking/networks/list.
  2. Click the name of a subnet to display the Subnet details page.
  3. Click the EDIT button.
  4. Set Flow Logs to On.
  5. Click Save.

CLI Command

To set Private Google access for a network subnet, run the following command:

gcloud compute networks subnets update [SUBNET_NAME] 
--region [REGION] 

Fix - Buildtime


  • Resource: google_compute_subnetwork
  • Argument: log_config
resource "google_compute_subnetwork" "example" {
  name          = "log-test-subnetwork"
  ip_cidr_range = ""
  region        = "us-central1"
  network       = google_compute_network.custom-test.id

+ log_config {
    aggregation_interval = "INTERVAL_10_MIN"
    flow_sampling        = 0.5
    metadata             = "INCLUDE_ALL_METADATA"