Flow Logs: VPC Subnets
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1h 19m

Creating and configuring a Virtual Private Cloud (VPC) within AWS can be a simple or difficult process. It all very much depends on the complexity of your requirements. For example, how many subnets and hosts will you require? Will you be using one VPC or peering multiple VPCs together? Do you need to establish connectivity back to your on-premise network? Do you need internet connectivity for your Private instances? These and many more questions need to be asked and answered before you start to design your VPC infrastructure.

As a part of this process, you will need to understand VPC Subnet configurations and VPC routing to ensure you architect your solution correctly and efficiently.

This AWS Virtual Private Cloud: Subnets and Routing course looks and VPC Subnets and VPC Routing in detail, providing examples of both across different configurations and solutions and how to best implement your network design.

Course lectures

VPC Subnets:

  • VPC CIDR Blocks - This lecture focuses on the effect of subnetting your VPC CIDR Block
  • Why Subnet your VPC - This lecture looks at some of the reasons why you may want to subnet your VPC, by looking at the advantages and benefits
  • VPC Subnets - This lecture dives into at what a VPC Subnet looks like within the Management Console and its associated components such as Network Access Control Lists (NACLs)
  • Public & Private Subnets - This lecture looks at the differences between both Public and Private subnets within a VPC
  • VPC Peering: Subnet Considerations - This lecture focuses on some of the considerations when architecting your subnets in different VPC Peering configurations
  • Flow Logs: VPC Subnets - This lecture dives into at what a VPC Subnet looks like within the Management Console and its associated components such as Network Access Control Lists (NACLs)
  • Demonstration: Creating a VPC & Subnets - This lecture provides a demonstration on how to set up and configure a VPC with both Public and Private subnets

VPC Routing:

  • Routing Fundamentals & Route Tables - This lecture introduces AWS routing and its Routing tables by breaking down all the components within it
  • Routing Priorities - This lecture explains how the routing priorities are defined for overlapping routes within the same route table
  • Routing: VPC Peering - This lecture looks are different routing configurations for multiple VPC peering scenarios
  • Routing: VPN Connection via a Virtual Private Gateway - This lecture looks at routing configurations for virtual Private Gateways
  • Routing: Internet Gateways & NAT Gateways - This lecture looks at the routing configurations for both IGWs and NAT Gateways and the dependencies involved
  • Routing: VPC Endpoints - This lecture looks at the automatic routing configuration when creating a VPC Endpoint

Hello, and welcome to this short lecture examining flow logs for VPC subnets. As you create more and more subnets within your VPC, each with their own network access controls and route table, it won't be long before you start to encounter communication issues with certain subnets not being able to talk to others over specific ports, or traffic is not being routed as expected.

When you start to troubleshoot these kinds of problems, you're going to wish you have a helping hand. Within AWS, that comes in the form of VPC flow logs. These flow logs capture IP traffic going in and out of your network interfaces. And these flow logs can be created for subnets, your entire VPC, or even a single interface.

Once activated, the login information is sent to a CloudWatch log group, where you are able to filter information and monitor specific metrics. To set up flow logs for your subnet, first select Subnets within the VPC service in the management console. Select your subnet, select Subnet actions, select Create Flow Log.

You will then be prompted to enter a number of details to complete the setup. Let's take a look at these.
- The filter. This allows you to specify the type of traffic to log. Available options are, all, accept, or reject.
- The role. As flow logs need to be able to publish data to a CloudWatch log group, permission is required in the form of a role. This role has five actions in the policy, and will look like the following. You must remember to ensure that the flow log service also has permission to assume the role itself, which can be added by modifying the trust relationship of the role to include the following policy.
- The destination log group name. Here you must enter the name of a CloudWatch log in which the data will be published to.

Once your subnet flow logs are set up, you will then be able to configure CloudWatch to monitor specific metrics with filters and use SNS to configure notifications for specific events. For more information on CloudWatch, please see our existing course here.

Coming up in the next lecture, I will be providing a demonstration on how to create a new VPC and configure both public and private subnets.

About the Author
Learning Paths

Stuart has been working within the IT industry for two decades covering a huge range of topic areas and technologies, from data center and network infrastructure design, to cloud architecture and implementation.

To date, Stuart has created 150+ courses relating to Cloud reaching over 180,000 students, mostly within the AWS category and with a heavy focus on security and compliance.

Stuart is a member of the AWS Community Builders Program for his contributions towards AWS.

He is AWS certified and accredited in addition to being a published author covering topics across the AWS landscape.

In January 2016 Stuart was awarded ‘Expert of the Year Award 2015’ from Experts Exchange for his knowledge share within cloud services to the community.

Stuart enjoys writing about cloud technologies and you will find many of his articles within our blog pages.