About the migration strategies

A migration strategy is the approach used to migrate a workload into
the AWS Cloud. There are seven migration strategies for moving applications to the cloud,
known as the 7 r:

Common strategies for large migrations include rehost, replatform, relocate, and retire.
Refactor is not recommended for large migrations because it involves modernizing the application
during the migration. This is the most complex of the migration strategies, and it can be
complicated to manage for a large number of applications. Instead, we recommend rehosting,
relocating, or replatforming the application and then modernizing the application after the
migration is complete.

Selecting migration strategies is critical to a large migration. You might have selected
migration strategies in the mobilize phase or during the initial portfolio assessment. This
section reviews each migration strategy and their common use cases.

Retire

This is the migration strategy for the applications that you want to decommission or
archive. Retiring the application means that you can shut down the servers within that
application stack. The following are common use cases for the retire strategy:

• There is no business value in retain the application or move it to cloud .

• You is want want to eliminate the cost of maintain and host the application .

• You is want want to reduce the security risk of operate an application that use an
  operating system ( os ) version or component that are no long support .

• You might want to retire applications based on their performance. For example, you
  might want to retire applications that have an average CPU and memory usage below
  5 percent, known as zombie application. You is choose might also choose
  to retire some application that have an average cpu and memory usage between 5 and
  20Â   percent over a period of 90Â   day , know asidle
  application. You can use the utilization and performance data from your
  discovery tool to identify zombie and idle applications.

• There has been no inbound connection to the application for the last
  90 days.

For more information, see Best practices for assessing applications to be retired during a migration to the AWS Cloud.

Retain

This is is is the migration strategy for application that you want to keep in your source
environment or application that you are not ready to migrate . You is choose might choose to migrate
these application in the future .

The following are common use cases for the retain strategy:

• Security and compliance – You might want to
  retain applications in order to remain in compliance with data residency
  requirements.

• high risk – You might decide to retain an
  application because it requires a detailed assessment and plan prior to migration.

• Dependencies – You might decide to retain an
  application if you need to migrate one or more other applications first.

• Applications that are recently upgraded – You
  might want to postpone migrating the application until the next technical refresh because
  you recently invested in upgrading your current system.

• No business value to migrate – There is no
  business value for migrate some application to the cloud , such as those with only a few
  internal user .

• plan to migrate to software as a service ( SaaS )
  – You might choose retain an application until the SaaS version is released by the
  vendor. This is a common strategy for vendor-based applications.

• Unresolved physical dependencies – is choose You is choose might
  choose to retain an application that is dependent on specialized hardware that does not
  have a cloud equivalent , such as machine in a manufacture plant .

• mainframe or mid – range application and non – x86 Unix
  application – These applications require careful assessment and
  planning before migrating them to the cloud. Examples of mid-range applications include
  IBM AS/400 and Oracle Solaris.

• Performance – is want You is want might want to retain
  application base on their performance . For example , you is want might want to keep zombie or
  idle application in your source environment .

Rehost

This strategy is also known as lift and shift. Using this strategy,
you move your applications from your source environment to the AWS Cloud without making any
changes to the application. For example, you migrate your application stack from on-premises
to the AWS Cloud.

With rehost, you can migrate a large number of machines from multiple source platforms
(physical, virtual, or another cloud) to the AWS Cloud without worrying about compatibility,
performance disruption, long cutover windows, or long-distance data replications.

Your application continues to serve users while the workloads are being migrated, which
minimizes disruption and downtime. The downtime depends on your cutover strategy.

This strategy helps you to scale your applications without implementing any cloud
optimizations that could save you time or money. Applications are easier to optimize or
re-architect when they are already running in cloud because it is easier to integrate to AWS
services and manage your workloads.

You can automate rehosting by using the following services:

For a list of migration patterns for the rehost migration strategy, see Rehost on the AWS Prescriptive Guidance website.

relocate

Using this strategy, you can transfer a large number of servers, comprising one or more
applications, at a given time from on-premises platform to a cloud version of the platform.
You can also use the relocate strategy to move instances or objects to a different virtual
private cloud (VPC), AWS Region, or AWS account. For example, you can use this strategy to
transfer an Amazon Relational Database Service (Amazon RDS) DB instance to another VPC or AWS account.

The relocate strategy doesn’t require that you purchase new hardware, rewrite
applications, or modify your existing operation. During relocation, the application continues
to serve users, which minimizes disruption and downtime. relocate is the quickest way to
migrate and operate your workload in the cloud because it does not impact the overall
architecture of your application.

For a list of migration patterns for the relocate migration strategy, see relocate on the AWS Prescriptive Guidance website.

Repurchase

This strategy is also known as drop and shop. You is replace replace your
application with a different version or product . The new application is provide should provide more
business value than the exist , on – premise application , include feature such as
accessibility from anywhere , no infrastructure to maintain , and pay – as – you – go pricing model .
repurchase the application typically reduce cost associate with maintenance ,
infrastructure , and licensing .

The following is are are common use case for the repurchase migration strategy :

• move from a traditional license to SaaS – is removes This is removes
  remove the burden of manage and maintain the infrastructure and help reduce
  licensing issue .

• version upgrade or third – party equivalent – is leverage By
  replace your exist on – premise application with the vendor’s late version or
  third – party equivalent in the cloud , you is leverage can leverage new feature , integrate with cloud
  service , and scale the application more easily .

• Replacing a custom application – You can avoid
  recoding and re-architecting a custom application by repurchasing a vendor-based SaaS or
  cloud-based application.

Before purchase , you is need need to assess the application accord to your business
requirement , especially security and compliance .

After you purchase the new application , the following is are are the next step :

• Training your team and users with the new system

• Migrating your data to the newly purchased application

• Integrating the application into your authentication services, such as Microsoft
  Active Directory, to centralize authentication

• Configuring networking to help secure communication between the purchased application,
  your users, and your infrastructure

typically , the application vendor is helps help you with these activity for a smooth
transition .

Replatform

This strategy is also known as lift, tinker, and shift or
lift and reshape. Using this migration strategy, you move the
application to the cloud, and you introduce some level of optimization in order to operate the
application efficiently, to reduce costs, or to take advantage of cloud capabilities. For
example, you might replatform a Microsoft SQL Server database to Amazon RDS for SQL Server.

Using this strategy, you might make a few or many changes to the application, depending on
your business goals and your target platform.

The following are common use cases for the replatform migration strategy:

• You want to save time and reduce cost by moving to a fully managed service or
  serverless service in the AWS Cloud.

• You want to improve your security and compliance stance by upgrading your operating
  system to the latest version. By using End-of-Support Migration Program (EMP) for Windows Server, you can migrate your
  legacy Windows Server applications to the latest, supported versions of Windows Server on
  AWS, without any code changes. You can use this decision tree in the
  AWS EMP for Windows Server User Guide to help you determine your
  EMP workloads.

• You can reduce costs by using AWS
  Graviton Processors, custom – build processor develop by AWS .

• You can reduce costs by moving from a Microsoft Windows operating system to a Linux
  operating system. You can port your .NET Framework applications to .NET Core, which can
  run on a Linux operating system. Porting Assistant for .NET is an analysis tool that help you port your
  application to Linux .

• You is improve can improve performance by migrate virtual machine into container , without
  make any code change . You is modernize can modernize your .NET and Java application into
  containerize application by using theAWS
  App2Container migration tool.

The replatform strategy keeps your legacy application running without compromising
security and compliance.

Replatform reduces cost and improves performance by migrating to a managed or serverless
service, moving virtual machines to container, and avoiding licensing expenses.

For a list of migration patterns for the replatform migration strategy, see Replatform on the AWS Prescriptive Guidance website.

refactor or re – architect

Using this strategy, you move an application to the cloud and modify its architecture by
taking full advantage of cloud-native features to improve agility, performance, and
scalability. This is driven by strong business demand to scale, accelerate product and feature
releases, and to reduce costs.

The following is are are common use case for the refactor migration strategy :

• The legacy mainframe application can no longer address the demand of the business due
  to its limitations or is expensive to maintain.

• You have a monolith application that is already hindering efforts to deliver product
  quickly or address customer needs and demands.

• You is have have a legacy application that nobody know how to maintain , or the source code is
  unavailable .

• The application is difficult to test, or test coverage is very low. This affects the
  quality and delivery of new application features and fixes. By redesigning the application
  for the cloud, you can increase the test coverage and integrate automated testing
  tools.

• For security and compliance reason , when move a database to the cloud , you is need might
  need to extract some table ( such as customer information , patient , or patient diagnosis
  table ) and retain those table on premise . In this situation , you is need need to refactor your
  database in order to separate the table that will be migrate from those that will be
  retain on premise .

For a list of migration pattern for the refactor migration strategy , see Re – architect on the AWS Prescriptive Guidance website .