Access flow logs

This page describes how to access flow logs by using Cloud Logging.

Access flow logs in the Logs Explorer

You can view VPC Flow Logs by using the Logs Explorer. In the Logs Explorer, you can use resource filters and queries to view your flow logs.

Configure IAM

To configure access control for logging, see the access control guide for Logging.

Access flow logs by using resource filters

To view all flow logs or flow logs for a specific subnet, see the following sections. You can also view these logs by using Logs Explorer queries, as described in Access flow logs by using queries.

Access all flow logs

Console

  1. In the Google Cloud console, go to the Logs Explorer page.

    Go to Logs Explorer

  2. Click All resources.

  3. In the Select resource list, click Subnetwork and then click Apply.

  4. Click Log name.

  5. In the Select log names list, click vpc_flows and then click Apply.

Access flow logs for a specific subnet

Console

  1. In the Google Cloud console, go to the Logs Explorer page.

    Go to Logs Explorer

  2. Click All resources.

  3. In the Select resource list, click Subnetwork.

  4. In the Subnetwork ID list, select the subnet and then click Apply.

  5. In the Select log names list, click vpc_flows and then click Apply.

Access flow logs by using queries

Console

  1. In the Google Cloud console, go to the Logs Explorer page.

    Go to Logs Explorer

  2. If you don't see the query editor field in the Query pane, click the Show query toggle.

  3. In the query editor field, enter a query. For example, to view flow logs for a specific subnet, enter the following query, replacing PROJECT_ID with your project ID and SUBNET_NAME with your subnetwork:

    resource.type="gce_subnetwork"
logName="projects/PROJECT_ID/logs/compute.googleapis.com%2Fvpc_flows"
resource.labels.subnetwork_name="SUBNET_NAME"

    For more examples of queries that you can run to view your flow logs, see Examples of Logs Explorer queries for VPC Flow Logs.

  4. Click Run query.

Examples of Logs Explorer queries for VPC Flow Logs

The following table provides examples of Logs Explorer queries that you can run to view your flow logs.

Logs you want to view Query
All logs 
resource.type="gce_subnetwork"
logName="projects/PROJECT_ID/logs/compute.googleapis.com%2Fvpc_flows"
Logs for a specific subnet 
resource.type="gce_subnetwork"
logName="projects/PROJECT_ID/logs/compute.googleapis.com%2Fvpc_flows"
resource.labels.subnetwork_name="SUBNET_NAME"
Logs for a specific VM 
resource.type="gce_subnetwork"
logName="projects/PROJECT_ID/logs/compute.googleapis.com%2Fvpc_flows"
jsonPayload.src_instance.vm_name="VM_NAME"
Logs for traffic to a specific subnet range 
resource.type="gce_subnetwork"
logName="projects/PROJECT_ID/logs/compute.googleapis.com%2Fvpc_flows"
ip_in_net(jsonPayload.connection.dest_ip, SUBNET_RANGE)
Logs for a specific GKE cluster 
resource.type="k8s_cluster"
logName="projects/PROJECT_ID/logs/vpc_flows"
resource.labels.cluster_name="CLUSTER_NAME"
Logs for only egress traffic from a subnet 
logName="projects/PROJECT_ID/logs/compute.googleapis.com%2Fvpc_flows" AND
jsonPayload.reporter="SRC" AND
jsonPayload.src_vpc.subnetwork_name="SUBNET_NAME" AND
(jsonPayload.dest_vpc.subnetwork_name!="SUBNET_NAME"
 OR NOT jsonPayload.dest_vpc.subnetwork_name:*)
Logs for all egress traffic from a VPC network 
logName="projects/PROJECT_ID/logs/compute.googleapis.com%2Fvpc_flows" AND
jsonPayload.reporter="SRC" AND
jsonPayload.src_vpc.vpc_name="VPC_NAME" AND
(jsonPayload.dest_vpc.vpc_name!="VPC_NAME" OR NOT jsonPayload.dest_vpc:*)
Logs for an individual destination port 
resource.type="gce_subnetwork"
logName="projects/PROJECT_ID/logs/compute.googleapis.com%2Fvpc_flows"
jsonPayload.connection.dest_port=PORT
jsonPayload.connection.protocol=PROTOCOL
Logs for multiple destination ports 
resource.type="gce_subnetwork"
logName="projects/PROJECT_ID/logs/compute.googleapis.com%2Fvpc_flows"
jsonPayload.connection.dest_port=(PORT1 OR PORT2)
jsonPayload.connection.protocol=PROTOCOL

Replace the following:

  • PROJECT_ID: the project ID.
  • SUBNET_NAME: the name of your subnetwork.
  • VM_NAME: the name of your VM.
  • SUBNET_RANGE: a CIDR range, such as 192.168.1.0/24.
  • CLUSTER_NAME: the name of your GKE cluster.
  • VPC_NAME: the name of your VPC network.
  • PORT1 and PORT2: the destination ports.
  • PROTOCOL: the communication protocol.

Route logs to BigQuery, Pub/Sub, and custom targets

You can route flow logs from Logging to a destination of your choice as described in the Routing and storage overview in the Logging documentation. Refer to the previous section for example filters.

Troubleshooting

No vpc_flows appear in Logging for the gce_subnetwork resource

  • Confirm that logging is enabled for the given subnet.
  • VPC flows are only supported for VPC networks. If you have a legacy network, you won't see any logs.
  • In Shared VPC networks, logs only appear in the host project, not the service projects. Make sure that you look for the logs in the host project.
  • Logging exclusion filters block specified logs. Make sure that there are no exclusion rules that discard VPC Flow Logs:
    1. Go to Log router.
    2. In the More actions menu for your logging bucket, click View sink details.
    3. Make sure that there are no exclusion rules that might discard VPC Flow Logs.

No RTT or byte values on some of the logs

  • RTT measurements may be missing if not enough packets were sampled to capture RTT. This is more likely to happen for low volume connections.
  • RTT values are available only for TCP flows.
  • Some packets are sent with no payload. If header-only packets were sampled, the bytes value will be 0.

Some flows are missing

  • Ingress packets are sampled after ingress VPC firewall rules. Make sure that there aren't any ingress firewall rules that deny the packets that you expect to be logged. If you're not sure whether VPC firewall rules are blocking ingress packets, you can enable Firewall Rules Logging and inspect the logs.
  • Only TCP, UDP, ICMP, ESP, and GRE protocols are supported. VPC Flow Logs does not support any other protocols.
  • Logs are sampled. Some packets in very low volume flows might be missed.

Missing GKE annotations in some logs

Make sure that your GKE cluster is a supported version.

Missing logs for some GKE flows

Make sure Intranode visibility is enabled in the cluster. Otherwise, flows between Pods on the same node are not logged.

What's next