Flow log records

A flow log record represents a network flow in your VPC. By default, each record captures a network internet protocol (IP) traffic flow (characterized by a 5-tuple on a per network interface basis) that occurs within an aggregation interval, also referred to as a capture window.

Each record is a string with fields separated by spaces. A record includes values for the different components of the IP flow, for example, the source, destination, and protocol.

When you create a flow log, you can use the default format for the flow log record, or you can specify a custom format.

Aggregation interval

The aggregation interval is the period of time during which a particular flow is captured and aggregated into a flow log record. By default, the maximum aggregation interval is 10 minutes. When you create a flow log, you can optionally specify a maximum aggregation interval of 1 minute. Flow logs with a maximum aggregation interval of 1 minute produce a higher volume of flow log records than flow logs with a maximum aggregation interval of 10 minutes.

When a network interface is attached to a Nitro-based instance, the aggregation interval is always 1 minute or less, regardless of the specified maximum aggregation interval.

After data is captured within an aggregation interval, it takes additional time to process and publish the data to CloudWatch Logs or Amazon S3. The flow log service typically delivers logs to CloudWatch Logs in about 5 minutes and to Amazon S3 in about 10 minutes. However, log delivery is on a best effort basis, and your logs might be delayed beyond the typical delivery time.

Default format

With the default format, the flow log records include the version 2 fields, in the order shown in the available fields table. You cannot customize or change the default format. To capture additional fields or a different subset of fields, specify a custom format instead.

Custom format

With a custom format, you specify which fields are included in the flow log records and in which order. This enables you to create flow logs that are specific to your needs and to omit fields that are not relevant. Using a custom format can reduce the need for separate processes to extract specific information from the published flow logs. You can specify any number of the available flow log fields, but you must specify at least one.

Available fields

The following table describes all of the available fields for a flow log record. The Version column indicates the VPC Flow Logs version in which the field was introduced. The default format includes all version 2 fields, in the same order that they appear in the table.

When publishing flow log data to Amazon S3, the data type for the fields depends on the flow log format. If the format is plain text, all fields are of type STRING. If the format is Parquet, see the table for the field data types.

If a field is not applicable or could not be computed for a specific record, the record displays a '-' symbol for that entry. Metadata fields that do not come directly from the packet header are best effort approximations, and their values might be missing or inaccurate.

Field	Description	Version
version	The VPC Flow Logs version. If you use the default format, the version is 2. If you use a custom format, the version is the highest version among the specified fields. For example, if you specify only fields from version 2, the version is 2. If you specify a mixture of fields from versions 2, 3, and 4, the version is 4. Parquet data type: INT_32	2
account-id	The AWS account ID of the owner of the source network interface for which traffic is recorded. If the network interface is created by an AWS service, for example when creating a VPC endpoint or Network Load Balancer, the record might display unknown for this field. Parquet data type: STRING	2
interface-id	The ID of the network interface for which the traffic is recorded. Parquet data type: STRING	2
srcaddr	For incoming traffic, this is the IP address of the source of traffic. For outgoing traffic, this is the private IPv4 address or the IPv6 address of the network interface sending the traffic. See also pkt-srcaddr. Parquet data type: STRING	2
dstaddr	The destination address for outgoing traffic, or the IPv4 or IPv6 address of the network interface for incoming traffic on the network interface. The IPv4 address of the network interface is always its private IPv4 address. See also pkt-dstaddr. Parquet data type: STRING	2
srcport	The source port of the traffic. Parquet data type: INT_32	2
dstport	The destination port of the traffic. Parquet data type: INT_32	2
protocol	The IANA protocol number of the traffic. For more information, see Assigned Internet Protocol Numbers. Parquet data type: INT_32	2
packets	The number of packets transferred during the flow. Parquet data type: INT_64	2
bytes	The number of bytes transferred during the flow. Parquet data type: INT_64	2
start	The time, in Unix seconds, when the first packet of the flow was received within the aggregation interval. This might be up to 60 seconds after the packet was transmitted or received on the network interface. Parquet data type: INT_64	2
end	The time, in Unix seconds, when the last packet of the flow was received within the aggregation interval. This might be up to 60 seconds after the packet was transmitted or received on the network interface. Parquet data type: INT_64	2
action	The action that is associated with the traffic: ACCEPT — The traffic was accepted. REJECT — The traffic was rejected. For example, the traffic was not allowed by the security groups or network ACLs, or packets arrived after the connection was closed. Parquet data type: STRING	2
log-status	The logging status of the flow log: OK — Data is logging normally to the chosen destinations. NODATA — There was no network traffic to or from the network interface during the aggregation interval. SKIPDATA — Some flow log records were skipped during the aggregation interval. This might be because of an internal capacity constraint, or an internal error. Some flow log records may be skipped during the aggregation interval (see log-status in Available fields). This may be caused by an internal AWS capacity constraint or internal error. If you are using AWS Cost Explorer to view VPC flow log charges and some flow logs are skipped during the flow log aggregation interval, the number of flow logs reported in AWS Cost Explorer will be higher than the number of flow logs published by Amazon VPC. Parquet data type: STRING	2
vpc-id	The ID of the VPC that contains the network interface for which the traffic is recorded. Parquet data type: STRING	3
subnet-id	The ID of the subnet that contains the network interface for which the traffic is recorded. Parquet data type: STRING	3
instance-id	The ID of the instance that's associated with network interface for which the traffic is recorded, if the instance is owned by you. Returns a '-' symbol for a requester-managed network interface; for example, the network interface for a NAT gateway. Parquet data type: STRING	3
tcp-flags	The bitmask value for the following TCP flags: FIN — 1 SYN — 2 RST — 4 SYN-ACK — 18 If no supported flags are recorded, the TCP flag value is 0. For example, since tcp-flags does not support logging ACK or PSH flags, records for traffic with these unsupported flags will result in tcp-flags value 0. If, however, an unsupported flag is accompanied by a supported flag, we will report the value of the supported flag. For example, if ACK is a part of SYN-ACK, it reports 18. And if there is a record like SYN+ECE, since SYN is a supported flag and ECE is not, the TCP flag value is 2. If for some reason the flag combination is invalid and the value cannot be calculated, the value is '-'. If no flags are sent, the TCP flag value is 0. TCP flags can be OR-ed during the aggregation interval. For short connections, the flags might be set on the same line in the flow log record, for example, 19 for SYN-ACK and FIN, and 3 for SYN and FIN. For an example, see TCP flag sequence. For general information about TCP flags (such as the meaning of flags like FIN, SYN, and ACK), see TCP segment structure on Wikipedia. Parquet data type: INT_32	3
type	The type of traffic. The possible values are: IPv4 | IPv6 | EFA. For more information, see Elastic Fabric Adapter. Parquet data type: STRING	3
pkt-srcaddr	The packet-level (original) source IP address of the traffic. Use this field with the srcaddr field to distinguish between the IP address of an intermediate layer through which traffic flows, and the original source IP address of the traffic. For example, when traffic flows through a network interface for a NAT gateway, or where the IP address of a pod in Amazon EKS is different from the IP address of the network interface of the instance node on which the pod is running (for communication within a VPC). Parquet data type: STRING	3
pkt-dstaddr	The packet-level (original) destination IP address for the traffic. Use this field with the dstaddr field to distinguish between the IP address of an intermediate layer through which traffic flows, and the final destination IP address of the traffic. For example, when traffic flows through a network interface for a NAT gateway, or where the IP address of a pod in Amazon EKS is different from the IP address of the network interface of the instance node on which the pod is running (for communication within a VPC). Parquet data type: STRING	3
region	The Region that contains the network interface for which traffic is recorded. Parquet data type: STRING	4
az-id	The ID of the Availability Zone that contains the network interface for which traffic is recorded. If the traffic is from a sublocation, the record displays a '-' symbol for this field. Parquet data type: STRING	4
sublocation-type	The type of sublocation that's returned in the sublocation-id field. The possible values are: wavelength | outpost | localzone. If the traffic is not from a sublocation, the record displays a '-' symbol for this field. Parquet data type: STRING	4
sublocation-id	The ID of the sublocation that contains the network interface for which traffic is recorded. If the traffic is not from a sublocation, the record displays a '-' symbol for this field. Parquet data type: STRING	4
pkt-src-aws-service	The name of the subset of IP address ranges for the pkt-srcaddr field, if the source IP address is for an AWS service. If the pkt-srcaddr belongs to an overlapped range, pkt-src-aws-service will only show one of the AWS service code. The possible values are: AMAZON | AMAZON_APPFLOW | AMAZON_CONNECT | API_GATEWAY | CHIME_MEETINGS | CHIME_VOICECONNECTOR | CLOUD9 | CLOUDFRONT | CODEBUILD | DYNAMODB | EBS | EC2 | EC2_INSTANCE_CONNECT | GLOBALACCELERATOR | KINESIS_VIDEO_STREAMS | ROUTE53 | ROUTE53_HEALTHCHECKS | ROUTE53_HEALTHCHECKS_PUBLISHING | ROUTE53_RESOLVER | S3 | WORKSPACES_GATEWAYS. Parquet data type: STRING	5
pkt-dst-aws-service	The name of the subset of IP address ranges for the pkt-dstaddr field, if the destination IP address is for an AWS service. For a list of possible values, see the pkt-src-aws-service field. Parquet data type: STRING	5
flow-direction	The direction of the flow with respect to the interface where traffic is captured. The possible values are: ingress | egress. Parquet data type: STRING	5
traffic-path	The path that egress traffic takes to the destination. To determine whether the traffic is egress traffic, check the flow-direction field. The possible values are as follows. If none of the values apply, the field is set to -. 1 — Through another resource in the same VPC, including resources that create a network interface in the VPC 2 — Through an internet gateway or a gateway VPC endpoint 3 — Through a virtual private gateway 4 — Through an intra-region VPC peering connection 5 — Through an inter-region VPC peering connection 6 — Through a local gateway 7 — Through a gateway VPC endpoint (Nitro-based instances only) 8 — Through an internet gateway (Nitro-based instances only) Parquet data type: INT_32	5
ecs-cluster-arn	AWS Resource Name (ARN) of the ECS cluster if the traffic is from a running ECS task. To include this field in your subscription, you need permission to call ecs:ListClusters. Parquet data type: STRING	7
ecs-cluster-name	Name of the ECS cluster if the traffic is from a running ECS task. To include this field in your subscription, you need permission to call ecs:ListClusters. Parquet data type: STRING	7
ecs-container-instance-arn	ARN of the ECS container instance if the traffic is from a running ECS task on an EC2 instance. If the capacity provider is AWS Fargate, this field will be '-'. To include this field in your subscription, you need permission to call ecs:ListClusters and ecs:ListContainerInstances. Parquet data type: STRING	7
ecs-container-instance-id	ID of the ECS container instance if the traffic is from a running ECS task on an EC2 instance. If the capacity provider is AWS Fargate, this field will be '-'. To include this field in your subscription, you need permission to call ecs:ListClusters and ecs:ListContainerInstances. Parquet data type: STRING	7
ecs-container-id	Docker runtime ID of the container if the traffic is from a running ECS task. If there are one or more containers in the ECS task, this will be the docker runtime ID of the first container. To include this field in your subscription, you need permission to call ecs:ListClusters. Parquet data type: STRING	7
ecs-second-container-id	Docker runtime ID of the container if the traffic is from a running ECS task. If there are more than one containers in the ECS task, this will be the Docker runtime ID of the second container. To include this field in your subscription, you need permission to call ecs:ListClusters. Parquet data type: STRING	7
ecs-service-name	Name of the ECS service if the traffic is from a running ECS task and the ECS task is started by an ECS service. If the ECS task is not started by an ECS service, this field will be '-'. To include this field in your subscription, you need permission to call ecs:ListClusters and ecs:ListServices. Parquet data type: STRING	7
ecs-task-definition-arn	ARN of the ECS task definition if the traffic is from a running ECS task. To include this field in your subscription, you need permission to call ecs:ListClusters and ecs:ListTaskDefinitions Parquet data type: STRING	7
ecs-task-arn	ARN of the ECS task if the traffic is from a running ECS task. To include this field in your subscription, you need permission to call ecs:ListClusters and ecs:ListTasks. Parquet data type: STRING	7
ecs-task-id	ID of the ECS task if the traffic is from a running ECS task. To include this field in your subscription, you need permission to call ecs:ListClusters and ecs:ListTasks. Parquet data type: STRING	7
reject-reason	Reason why traffic was rejected. Possible values: BPA. Returns a '-' for any other reject reason. For more information about VPC Block Public Access (BPA), see Block public access to VPCs and subnets. Parquet data type: STRING	8