Understanding VPC Flow Logs
VPC Flow Logs are a feature that enables you to capture and log information about the network traffic going to and from the designated network interfaces within your VPC. This provides a single source of information for monitoring different aspects of your VPC.
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Overview of VPC Flow Logs
VPC flow logs are a powerful tool provided by Amazon Web Services that provides deep insight into the flow of traffic to and from a Virtual Private Cloud (VPC). With VPC flow logs, administrators can monitor network performance, analyze network usage and optimize network expenses, and perform network forensics in the event of an incident.
Types of VPC Flow Logs
When configuring VPC Flow Logs, it is important to understand what is being monitored and how the logs compile the data. AWS offers flow logging at three levels:
1. Virtual Private Cloud (VPC): Flow logs can be enabled for a particular VPC to monitor all activity within the cloud environment.
2. Subnet: VPCs are often divided into subnets that span multiple availability zones within a region. A subnet is a range of IP addresses within the VPC. Flow Logs can be created for a specific subnet to monitor all activity within the subnet.
3. Elastic Network Interface (ENI): ENIs are virtual network cards that can be attached to EC2 instances to enable network connectivity. Flow logs can be captured from these interfaces to monitor latency and malicious activity.
Enabling VPC Flow Logs
VPC flow logs can be enabled from the AWS Management Console, the AWS Command Line Interface (CLI), or using the EC2 API. When creating a flow log, the user needs to specify the resource to be monitored, the type of traffic to be captured (accepted traffic, rejected traffic, or all traffic), and the destination to which the flow log data should be published.
Publishing Flow Logs
VPC Flow Logs can be sent to either CloudWatch Logs or an S3 bucket. In the case of CloudWatch Logs, a log group must be created. For an S3 bucket, the user needs to specify an existing S3 bucket.
VPC Flow Logs Use Cases
VPC flow logs can be used for network monitoring, network usage optimization, and network forensics.
Network Monitoring: VPC flow logs provide real-time visibility into network throughput and performance.
Network Usage: Analyzing the network usage can help optimize the network traffic expenses.
Network Forensics: Compromised IPs can be identified by analyzing all the incoming and outgoing network flows.
VPC Flow Logs Limitations
VPC flow logs cannot be enabled for VPCs that are peered with the VPC unless the VPC is in the same account. Furthermore, once a flow log is created, its configuration and flow record format cannot be changed. Additionally, certain types of traffic are excluded, such as DHCP traffic, mirrored traffic, traffic generated by a Windows instance for Amazon windows license activation, and DNS activity.
Conclusion
VPC flow logs offer a powerful way to gain insight into the traffic of a VPC. It is important to understand how to enable, configure, and publish flow logs, as well as the limitations and pricing of flow logs, in order to get the most out of the service.