Landing Zone in AWS – Introduction

Cloud adoption has gone through phases. Hashicorp’s CTO Armon Dadgar has a great stream on Hashcorp’s narrative of the three Phases of Cloud Adoption:

  • Phase 1, with main focus on agility, app teams in wild west, account sprawl, inconsistent configuration, security & compliance challenge
  • Phase 2. consistent platform layer providing an opinionated way of configurations, security and compliance control, introduction of platform team, whose customers are application team, scaling challenges with platform team capacity not keeping up with application team’s demand
  • Phase 3. self-service platform at scale for many application teams. CICD, infra-as-code

New greenfield clients today should aim at phase 2 or phase 3 depending on their target operation size. Either way, they need a landing zone for consistency. This post focuses on the landing zone options on AWS and the key constructs.


AWS Prescriptive Guidance defines landing zone as a well-architected (secure, scalable, compliant, etc), multi-account AWS environment that is a secure baseline from which you can deploy workloads and applications. A landing zone may consists of:

  • Multi-account architecture
  • Identity and Access management solution
  • Governance, compliance, logging and auditing solutions
  • Security and networking design

Landing zone reflects an enterprise opinion on how to configure networking and IAM. Establishing a landing zone can be a very involving process. In early days of cloud operation people used build landing zone by “clickops” on AWS console, which cannot keep up with the growth of landing zone and associated security services. Compared to SMB clients, some sectors such healthcare and national security have much more regulations and compliance frameworks.

In fact, landing zone is such a buzzword that I have learned to be very sensitive to the context. If a solution has words “landing zone” in its name, given the complexity and loose use of the words, there is a good chance that the solution only delivers some of the aspects above. Cloud consultants are still to address the gaps. Therefore I decided to write this post about what I learned about landing zone in AWS.

Multi-account and Organization

Since 2017, AWS has been officially advocating the use of multiple accounts as a best practice and security strategy. They encourage clients to view an account as a resource container, just like Resource Group in Azure (here is an article on the account structure between AWS and Azure) Client builds an account for security boundary and financial container. Many blog post came along (such as this one) on the implementation details. From tooling perspective, AWS launched AWS Organization in 2017 to facilitate multi-account management. This presentation from re:Inforce 2019 is a good material to understand multi-account environment with AWS Organizations. In 2021, AWS published a new white paper on best practices with multiple accounts. My previous coworkers authored two blog posts here and here to reflect multi-account setup as of late 2020.

AWS Organization is an account management service that provides a vehicle to centrally manage AWS accounts by groups, which brings many benefits, such as centralized logging, compliance management, consolidated billing, etc. As an administrator, you can create accounts in your organization and invite existing accounts to join the organization.

Typical account structure involves:

  • A root organization named Root
  • A organization hierarchy with one or more OUs under root, with each OU having one or more child OUs.
  • Each OU can have multiple accounts, with each account having one email address.

You can also configure service control policies (SCPs), a type of organization-level policy that you can use to manage permissions in your organization. SCPs offer central control over the maximum available permissions for all accounts in your organization. SCPs are a means of implementing guardrails in your AWS organization.

From Landing Zone Solution (ALZ) to Control Tower

To help client start with landing zone in AWS, in 2018 AWS introduced Landing Zone solutions (ALZ) which focuses on multi-account best practices. In 2019, AWS introduced Control Tower service, to provision multiple accounts for management, centralized logging and auditing. According to this page, we can customize customization Control Tower based Landing Zone in these ways:

  • AWS Control Tower console:
    • Instead of creating OU in AWS organization, do it under Control Tower in the console, as I did above under “create required OUs”.
  • Outside of AWS Control Tower console
    • using Account Factory for Terraform (AFT): Terraform-based account provisioning pipeline, for heavy Terraform shops.
    • using Customizations for AWS Control Tower (CfCT) solution. The LZ created remains in sync with Control Tower.
      • You first launch a standardized CF stack to set up the mechanisms for customization.
      • Then you create a custom package to define the customization. This includes a manifest file.

On the other hand, the original ALZ solution is currently in long-term support and will not receive any additional features. It is deprecated. AWS advises its customers migrate to AWS Control Tower based landing zone. The ALZ page is redirected to a page about customizing Control Tower landing zone.

The Control Tower based landing zone configures OUs, accounts, SSO and guardrails. It however does not entail networking design except for the guardrails.

Security Reference Architecture (SRA)

SRA is a reference architecture and accompanying recommendations on AWS security services, and how they work together in a multi-account environment to host a single-page application. It comes with a repository to demonstrate how to configure a secure multi-account environment with Control Tower, CfCT, as well as security services. Alternatively, you can deploy it with CloudFormation StackSets. For fully automated deployment of this architecture, check out Landing Zone Accelerator down below.

AWS Security Environment Accelerator (ASEA)

Regulated customers often find they need to add additional controls and capabilities to be defined and setup outside of Control Tower. ASEA aims to remove the complexity of having to develop and maintain a separate codebase to manage the additional customizations, by providing a tool to help deploy and operate secure multi-account, multi-region AWS environments on an ongoing basis.

Overtime, as Control Tower introduces new capabilities to support the customizations required in heavily regulated environments, the capabilities will be removed from ASEA and enabled directly within the Control Tower managed service, further reducing operational burden. Read this for its relationship with ALZ and Control Tower.

ASEA was first released in late 2020. It covers more on networking design and has a fairly comprehensive installation process. ASEA primarily cater to government of Canada‘s PBMM Security Configuration Profile with an opinionated configuration. The first few revisions were referred to as PMBB architecture. While it provides a great reference architecture for highly regulated landing zone, it has not gotten much traction elsewhere. The recommendation going forward, is to use Landing Zone Accelerator, which incorporates the features and lessons learned from ASEA.

Landing Zone Accelerator (LZA)

First released in May 2022, the Landing Zone Accelerator on AWS solution deploys a cloud foundation that is architected to align with AWS best practices and multiple global compliance frameworks. LZA operates on top of Control Tower managed landing zone. This page in the documentation brings a good explanation of how it works. Basically it employs CodeBuild as an orchestration engine, and leverages CDK to drive resource deployment. There are two repositories: the GitHub repository for Landing Zone Accelerator itself, and a CodeCommit configuration repository provisioned during preparation.

As document states, LZA is a fully automated implementation of the architecture guidelines documented in the SRA. LZA also incorporates features and lessons learned from ASEA and Compliant Framework for Federal and DoD Workloads in GovCloud (US), neither of which are recommended for new deployment. In addition, LZA aims to enable iterations and extensions of a secure environment over time. The vision is to eventually replace AFT, CfCT, and ASEA. As AWS releases newer versions of LZA, client should be able to upgrade it in a pipeline run.

Baseline architecture by LZA

The Landing Zone Accelerator project also provides a samples configurations in each regulated frameworks. For example, the healthcare best practice come up in Oct 2022 for healthcare industry. The healthcare best practice sample incorporates healthcare specific configurations, such as the detective guardrails defined in the Operational Best Practices for HIPAA Security  conformance pack. To deploy the best practices, modify the configuration in config repo, and run the pipeline again.

Landing Zone Options

To summarize, we have the following landing zone options in AWS:

Orchestration LayerLifecycleSummary
AWS Landing Zone Solution (ALZ)Introduced in June 2018.
Development stopped since June 2019.
Do not deploy ALZ. Existing ALZ accounts should migrate to Control Tower.
AWS Control TowerGA in June 2019To customize the landing zone, use AWS console, or alternatively, one of the following three options:
– CfCT: Customization for Control Tower
– AFT: Account Factory Terraform
– AFC: Account Factory Customizations
For example, CfCT can be used to deploy Security Reference Architecture (SRA)
AWS Secure Environment Accelerator (ASEA)Released 2020Canadian Centre for Cyber Security (CCCS) Medium Cloud Control Profile, formerly known as PBMM. This approach will be replaced by LZA
AWS Landing Zone Accelerator (LZA)Released in 2022A low-code deployment option. Samples provided in support of reference architectures that align with industry best practices or compliance frameworks. Examples for industry best practices:
– general best practice
– healthcare
– finance and tax
– education
Example for compliance frameworks:
– US state local government
– FedRAMP for US Federal and Department of Defence (DoD)
– CCCS Medium for Canadian government
– AWS Trusted Secure Enclave (TSE) Sensitive Edition (SE), which also aligns with other medium level security profiles such as NIST 800-53, ITSG-33, FedRAMP moderate, CCCS-Medium, IRAP, etc

If your organization has a compliance framework that LZA supports, it makes sense to start with LZA. Otherwise, it is sufficient to use Control Tower for multi-account setup.

Networking constructs

Landing zone involves multiple VPCs so it’s important to understand VPC peering and Transit Gateway. VPC peering can only be setup between two VPCs and transitive peering relationship is not supported. For 6 VPCs to talk to all each other, we’d need 15 peering setups, which is not sustainable. We have two options:

  • We can connect many VPCs to a single Transit Gateway and the VPCs will be able to talk to each other. We can also connect Transit Gateway to site-to-site VPN or Direct Connect. This is a good explanation.
  • We can still use peering, but dedicate one VPC as “Transit VPC” in a hub and spoke model.

When you attach a VPC to a transit gateway, you must specify one subnet from each AZ to be used by the transit gateway to route traffic. Specifying one subnet from an AZ enables traffic to reach resources in every subnet in that AZ.

Here is a comparison table. Read the white-paper “Building a Scalable and Secure Multi-VPC AWS Network Infrastructure” for more about network design. For example, Some clients need to inspect traffic. When deploying multiple VPCs, we also need to ensure DNS resolution works across VPCs, and between on-prem networks, by configuring Amazon DNS server.

Our VPCs also need to connect to managed AWS services. For services like S3 or DynamoDB (of the same or different account), workload in VPC can access them via public DNS. The traffic goes through Internet Gateway of VPC and then public Internet. It is neither secure nor economical. We often want all network traffic to stay on the global AWS backbone. There are three types of Endpoint under VPC to help us.

Gateway VPC Endpoint aka Gateway EndpointInterface VPC Endpoint aka Interface EndpointGateway Load Balancer Endpoint
PurposeVPC access native AWS servicesVPC access native AWS servicesVPC access your own service (aka Endpoint Service)
Enabled by Private LinkNoYesYes
Traffic remain on AWS networkYesYesYes
MechanismUse the public IP address of the service along with configuration in routing table to access target resource. The routing table acts as gateway. You can use the public DNS name of the service.Use private IP address from the VPC to access the target service. Require endpoint-specific DNS name for the target service. Incur extra charge. S3 as example. More secure because there is ENI in the VPC controlled by security group.Your Endpoint Services is hosted in front of a fleet of network virtual appliances. You can select endpoint type as you create it in console under VPC
Access from clients on premise or from other regionDoes NOT allow access from clients on premise or in VPC from other regionAllows access from clients on premise or clients in VPC from other regionAllowed

Private Link integrates with a subset of AWS services.

Security Constructs

AWS Network firewall is a configuration under VPC. You associate a Network Firewall with one or more subnets in the VPC. You also associate the Network Firewall with Firewall Policies. Each policy consists of rule groups. Each rule blocks or filters traffic. The log can be published to CloudWatch or S3 via Kinesis. Usecases of AWS Network firewall include:

  • inspect VPC-to-VPC traffic;
  • filter outbound traffic;
  • prevent inbound internet traffic;
  • secure AWS Direct Connect and VPN traffic

When you associate a firewall to your VPC, you must provide a subnet for each Availability Zone where you want to place a firewall endpoint to filter traffic

There are many points of configuration for firewall rules in AWS. AWS Firewall Manager is a place for central management. It connects with other services such as:

  • AWS WAF (L7)
  • AWS Network Firewall (L4)
  • AWS Shield (DDos)
  • Amazon Route 53 Resolver DNS Firewall
  • Security Groups
  • Third party firewall support

IAM Identity Center (previously AWS SSO) is for logging into AWS portal, giving each identity from an external identity store (such as AD) an identity on an AWS account. It addresses several challenges as a result of having multiple AWS accounts.

First, a user from AD needs to access multiple accounts. Second, in each account with access, s/he needs to have an IAM role. These IAM roles are based on attributes of his/her external identity, and can be different per AWS account. With Permission Set IAM Identity Center:

  • Allow you to login on different AWS account using the same credential
  • Allow you to federate with external identity store( e.g. using SAML)
  • Manage permission set for each account.

This video has a good walk-through of how to configure Azure AD as identity store, and tie it to specific AWS accounts and specify permission set.

Note that IAM Identity Center has a different purpose than Cognito. Cognito is to connect your app with an IdP. Your app can be an EC2-hosted application, serverless application on API gateway, or container-based application on Kubernetes, as long as the support open identity standards (e.g. OAuth 2.0, SAML 2.0 and OIDC). Cognito has two pools:

  • User pool for authentication. With a user pool, your app
  • Identity pool for authorization

So Cognito is for AuthN & AuthZ to your own app’s endpoint (business traffic) and it supports a number of standards. IAM Identity Center is for AuthN & AuthZ to your AWS account (management traffic). If you use it for your own application, your application user will have direct access your AWS resources. It mainly supports SAML (and OIDC but less used) and is commonly connected with Active Directory (Microsoft or AWS).

One can use AWS Directory Service to host a compatible and managed directory service. AWS Directory Service supports four modes:

  • AWS managed Microsoft AD: actual Microsoft Active Directory in AWS Cloud
  • Simple AD, powered by Linux-Samba Active Directory-compatible server
  • AD Connector: a proxy for redirecting directory request to your existing Microsoft AD without caching any information in the cloud
  • Cognito user pools

If you combine two AD domains, you will need domain trust.

Other security services

In addition to the core services above, LZA involves the following four services as well.

AWS Macie is a fully managed data security and privacy service based on ML and pattern matching. It continually evaluates your S3 environments to discovery PII and act on them. It also reports alerts on unencrypted buckets, publicly accessible buckets, etc.

AWS GuardDuty continuously analyze S3, container & instance workloads, user and accounts for potential threads, across account, based on ML for intelligent threat detection. In addition, GuardDuty also acts on findings.

AWS Config is an essential service that traces resource inventory, their changes and monitors for compliance:

  • When you turn on AWS Config, it first discovers the supported AWS resources in your account and generates a configuration item (poin-in-time view of attributes) for each resource. AWS Config also generates configuration items when the configuration of a resource changes, and it maintains historical records of the configuration items of your resources from the time you start the configuration recorder.
  • On an ongoing basis, AWS Config keeps track of all changes to your resources, whether or not it is initiated by the API
  • If you are using AWS Config rules, AWS Config continuously evaluates your AWS resource configurations for desired settings. You can deploy several related rules in a pre-built compliance pack.

As you may have noticed, there are many AWS services related to firewall, security and compliance. AWS Security Hub aims to be a a consolidated view of your security status in AWS. You can automate security checks, manage security findings, and identify the highest priority security issues across accounts in client environment. It can also:

  • consolidate security findings from GuardDuty, Inspector (vulnerability scanner and management), Macie, Config, Systems Manager, Firewall Manager, IAM Access Analyzer and other Integrated APN solutions
  • Check findings against best practices
  • Client can take action: i.e. investigate findings or take response and remediation actions


Landing zone deployment can take numerous iterations to finalize the requirement. It is important to have a vision of the client’s cloud operating model, which is usually discussed at the beginning of the adoption.