From Naive To Native

Migrating traditional server-based applications to the cloud and actually reaping the benefits.


Product DevelopmentAWSDevOpsTechnology


Oct 2021

Executive Summary

The rise of public cloud computing has been driven by hyper-scale online businesses like Amazon, Netflix and Google. Their platforms were born in the cloud and their success has been in a large part due to the flexibility and scale of cloud computing.

However, many organisations aren’t approaching cloud computing with a blank slate. They have existing applications or customers tied to older software architectures.

These organisations tend to have lacklustre or lukewarm experiences when moving to the cloud - failing to see the kind of benefits and cost savings they expect. In a 2019 paper from Unisys about 39% of businesses in Australia rated their cloud migration as “below expectations”.

While re-architecting for the cloud requires more investment, the value returned over time far exceeds the cost. Further, the cost can be spread over an extended period if you methodically tackle the problem and adopt new technologies in a step-by-step fashion.

Traditional Server Based Applications

Over the past 50 years the composition and nature of technology used in software applications has changed radically. Each stage of development from mainframe, to client server to service oriented architecture to the modern web stack has meant different tradeoffs and compromises.

While all of these may run on modern cloud infrastructure, modern cloud services have been designed with the highly parallel, asynchronous world of web applications in mind. Using a suboptimal architecture results in suboptimal outcomes in terms of cost, performance, reliability and the ability to innovate quickly.

To reap the benefits of public cloud computing, owners of traditional server based software should look to modernise their architectures in a structured way.

Common Architectural Patterns

Common Architectural PatternsCommon Architectural Patterns

Common Technology Stacks

Common Technology StacksCommon Technology Stacks

Modern Application Patterns

With the rise of ubiquitous compute resources in the form of public cloud services, a number of new patterns for software architecture have developed. Exemplified in the hyperscale web apps or Software-as-a-Service platforms they are surprisingly simple and flexible.

The philosophy which underpins modern software architectures is the 12-Factor App methodology. This highlights the key principles for building distributed software services that are scalable, resilient and efficient.

The implementation of these principles can be achieved with the following architectural patterns:

Modern Application PatternsModern Application Patterns

The Application Modernisation Journey

In general there are six choices when migrating applications to the cloud.

For custom built software, only three of them usefully apply:

  1. Rehost in the cloud using the same processes and technology as on-prem;
  2. Replatform by automating some of the underlying services or using managed services;
  3. Rearchitect the application to take advantage of higher levels of cloud maturity.

Ultimately the choice is based on the return on investment you wish to realise.

While re-architecting for the cloud requires more investment, the value returned over time far exceeds the cost. Further, the cost can be spread over an extended period as you break apart the problem and adopt new technologies in a step-by-step fashion.

Return on Investment over Time Return on Investment over Time

Technology Adoption Roadmap

It is important to learn how to manage your application effectively in the cloud before attempting to re-architect and optimise. By gathering data as you go you will be able to make the most effective decisions about how and where to optimise your architecture.

A serverless, cloud native, system is recommended for the long-term target architecture in order to minimise the total cost of ownership (TCO) and maximise reliability and development velocity.

The first step in the journey is to enable repeatable and reliable infrastructure through infrastructure-as-code, configured and deployed with an automated pipeline.

Then you should migrate to hybrid components, like an orchestrated container solution, to support a “Function-as-a-Service” deployment model. These can be implemented at a lower cost, can be continuously optimised and will enable a longer term re-architecture to a serveless model.

 “Function-as-a-Service” deployment model. “Function-as-a-Service” deployment model.

Ultimately, the higher levels of cloud maturity offer compelling benefits:

  • Developer effort can be redirected from the overhead of managing ‘plumbing’ to adding business value or delighting customers.
  • Cost efficiency is achieved by the metered usage of easily scalable resources.
  • Decomposition of services means they can be updated quickly and optimised individually. They can also be distributed geographically to increase reliability or reduce latency.

Cloud Maturity Ladder

Many organisations have had lacklustre experiences with cloud - failing to see the benefits and cost savings they expect. In a 2019 paper from Unisys, 39% of businesses in Australia rated their cloud migration as “below expectations”.

This is mainly because many treat public cloud services as ‘just another data centre’ - which fundamentally misses the point. Public cloud services evolved because existing data centres required a level of overhead and toil that companies like Amazon or Google could not sustain. Modern public cloud services all feature a layered service model designed to remove as much of the ‘undifferentiated heavy lifting’ as possible.

A failure to appreciate and leverage higher levels of cloud services will deliver disappointing results. Accessing these higher levels means gradually changing processes, capability and tooling in a methodical way over time.

Cloud Maturity LadderCloud Maturity Ladder

*Strangler Pattern - an architectural pattern that uses a facade or message tap to duplicate traffic to a service as a means to rewrite that service in place. Named after the Australian strangler fig.

Tenancy Model

The tenancy model is a key decision and determines the approach for managing the overall cloud footprint and in determining the architecture of the rest of the application. Tenancy refers to the number of customers that share resources at any given level of the application stack.

As with all design choices, there are tradeoffs to be made:

Single Tenant: Single compute instance (eg. server, container, VM) per customer. Single data store or database per customer All services and infrastructure are configured on a per customer basis, with complete segregation from any other customer.

Hybrid Tenant: Shared compute orchestration platform (e.g. Kubernetes cluster) -or- Shared data service (e.g managed database) but segregated data.

Multi Tenant: Shared compute & data instances (eg. microservices cluster, managed database) All services and infrastructure are shared between customers, with security policies and authorisation flows defining access control.

At a high level, the differences between multi and single tenant are:

Multi Tenancy v Single TenancyMulti Tenancy v Single Tenancy

A hybrid model is a choice based on how far along the scale is appropriate for your requirements. For example, resource utilisation may not be a concern, so deploying distinct infrastructure per customer may be feasible, but it will have significant cost implications.

Cloud Governance Strategy

Part of the benefit of cloud services is through distributed self-service models of delivery, (i.e. teams can provision the resources they need through self service-automation). This avoids delays and bottlenecks and enables speed, experimentation and innovation.

However if you deploy self-service options but retain a centralised governance structure then it will become a bottleneck which will throttle your productivity. The answer is to develop a rules based approach which delegates authority appropriately in line with your business objectives.

Your cloud governance model should be layered, with appropriate controls at each level:

Cloud GovernanceCloud Governance
Cloud FoundationsCloud Foundations

Organisational Guardrails

Guardrails are categorised into:

  1. Preventative Controls: prevent security events from occurring
  2. Detective controls: detect security events when they occur
  3. Remediation controls: react to security events to minimise their effect in a timely manner


Organisational GuardrailsOrganisational Guardrails

Cloud foundation controls and guardrails are applied at a number of layers:

  • Baseline controls: These are guardrails that you wish to apply to all accounts, plus any accounts you create in the future
  • Core patterns: These are patterns you wish to apply to the organisation, but what you apply and where may vary. Examples include:
    • Security cross-account roles
    • Central log auditing
    • Shared networking
  • Workload patterns: These are patterns you wish to apply to a particular type of workload.

Typical organisational guardrails that should be enabled include:

  • Geographic controls that limit where workloads can be spun up (preventative/baseline)
  • Prevent public access to object storage (preventative/baseline)
  • Whitelist allowed services in workload accounts (preventative/core pattern)
  • Enable detective controls like AWS Guard Duty across all accounts (detective/baseline)
  • Enable budgets and thresholds (detective/core pattern)
  • Automatically enable logging for new accounts & services (detective/core pattern)

Account Topology

There are multiple ways to set up AWS accounts within an organisation and costs and benefits to each approach. Note that an account structure is related to the tenancy model you select - the account model determines access and blast radius at the infrastructure level, while the tenancy model determines shared dependencies at the application level.

For example, a multi-tenant application could be spread across multiple accounts, with each account being geographically dependent (i.e. all the customers in a specific region).

In general follow these principles:

  • Group workloads based on business purpose and ownership
  • Apply distinct security controls by environment and risk profile
  • Constrain access to sensitive data
  • Limit the scope of impact from adverse events
  • Promote DevOps operating models where all the resources required to build and operate a workload are located within an account group which is available to a single team

Recommended Account Structure

Using AWS Organisational Units, you can further refine the structure of your account model:

Account StructureAccount Structure

DevOps Ways of Working

DevOps provides developers agility so they can deliver value to customers through the rapid delivery of software.

In principle this means an account per workload or application.

This has a number of benefits:

  1. Using a separate account per team or per product limits the blast radius of issues with that product to that product. For example, a change in the deployment pipeline or access controls for a particular product could bleed over into other products within the same account; a mistake in a deployment script could deny services to all applications which share the deployed services. Account separation prevents this.
  2. Further a separate account per workload makes that workload portable. Because accounts are effectively self-contained, if a workload ever transitions between teams, or teams are amalgamated, then you only need to handover the keys to that account and they have everything they need to develop and operate that workload.
  3. Finally tooling can be specific to the workload. This allows development teams the flexibility to choose their own stack, tools and methods, further increasing their agility. Centralised platform or tooling teams often become bottlenecks in their own right.

From a business perspective the separation of accounts allows costs to be tracked on a per-project/product basis. This enables investment decisions to be made with a much clearer line of sight to the operational costs associated with each system, and to consequently measure against benefits. It also allows direct comparisons between products and enables experiments to improve throughput within a particular product chain.

When managing large numbers of VMs, running COTs software, it is recommended to host these within an account per environment: such applications have minimal inter-dependencies and are usually managed by a centralised IT team - the overhead of managing multiple accounts outweighs the benefits in this instance. A "shared services" account is useful for these purposes.

Sandbox Accounts

Sandbox accounts provide a cloud playground to promote experimentation and capability development. Sandboxes can be assigned to individuals; pooled or shared within teams.

‘Innovation budgets’ using budget alerting is a simple way to manage costs without onerous approval processes: allocate an approved spend for experimentation. If the limit is exceeded, further approval or cleanup of unused resources is required.

Sandboxes should be fully isolated with no access to sensitive data - they are for experimentation purposes only.

Cautionary Tales from the Field

Given our experience with clients we have seen a number of examples where poor account structures have severely limited their ability to utilise cloud services.

  1. A large enterprise client with a single AWS account and a dozen teams would hit service limits on a monthly basis (e.g. network service limits) and while these are soft limits that can be altered, each time teams lost multiple days diagnosing and resolving issues through support channels.
  2. A smaller client ran all their workloads in the same account. Consequently there were multiple instances where developers deleted resources by accident. The most significant was where a developer accidentally deleted a production database table. Although it could be easily restored, it represented unnecessary risk, anxiety and effort.
  3. We have experienced many examples of clients with multiple tenants or workloads in the same account where one team has deleted or reconfigured a shared resource (like a VPC endpoint) or even mistaken another team's services for their own and broken multiple systems, including production. Accounts offer a clear boundary for delineation that aligns well with team and product boundaries.
  4. A smaller client migrated on premise VMs to the cloud. The COTS nature of many products and the fact that applications were managed by a centralised support team led to the workloads being co-located in a single “service” account with guardrails. In this instance, separating each VM into a separate workload account would have added unnecessary management overheads.

User Access and Identity Management

Manage access and identity centrally using a federated model based on existing organisational directory services. Replicate on premise directories to the cloud as a preparatory step, e.g using Azure AD, to support a modern standards based approach and phased migration.

SAML and OpenID Connect (OIDC) reduce vendor lock-in and support the use of Single Sign On (SSO) services.

Design Role Based Access Controls (RBAC) or Attribute Based Access Control (ABAC), to align user permissions with your organisational policies, mapping to the native Identity Management controls of your cloud provider. Manage system-to-system access control using cloud native controls to eliminate the need for secrets management and enforce a least-privilege model.

In general, we recommend:

  • Simple, light touch controls to reduce management overheads
  • Empowering users over controlling their actions
  • Auditing and engagement over prevention and approvals
  • Delegate permissions to minimise handoffs, and maximise flow:
  • Separating responsibilities through peer review (PR) rather than job functions
  • Avoid manual error by automating flows wherever possible

An effective identity management policy is important to control the organisational risk of unauthorised, or malicious, access. However, a one size fits all policy is not appropriate as complex identity management policies are overly restrictive and costly to maintain. As an organisation grows and the number of projects and value increases, the risk associated with a permissive structure grows.

Risk MitigationRisk Mitigation

Continuous Flow of Value

While the foundations of networking, accounts and infrastructure are essential they should be regarded as ‘plumbing’ which supports the true value of your digital enterprise – the applications that business users and customers require.

To that end, not only should the foundations be designed to operate with as little overhead as possible, they should be designed to support a flow of value in your organisation. They should be designed to allow the rapid and easy deployment of changes to infrastructure & applications.

The State of DevOps Report from Devops Research Associates (DORA) has directly linked Software Delivery and Operational (SDO) performance with organisational performance metrics like profitability and speed to market.

Further the report clearly identifies four key metrics which are proven to drive Software Delivery and Operational performance :

 Software Delivery and Operational performance Software Delivery and Operational performance

In order to maximise the long-term value you derive from your transition to a cloud architecture, you should:

  1. Collect historical data for these metrics based on your pre-cloud baseline
  2. Design your software delivery architecture with an eye to a step change improvement
  3. Build automated collection and measurement for each metric into your cloud reporting
  4. Set short and medium term improvement goals for each metric
  5. Implement small scale experiments as ‘proof of value’ evaluations
  6. Roll out successful experiments horizontally throughout your organisation
  7. Go to step 4 and repeat.

Infrastructure Deployment Patterns

The manual process of deploying, configuring and operating temperamental hardware has been largely replaced by commodity scale ‘infrastructure provisioned ‘as-code’ (IaaC).

The automation of infrastructure provisioning offers many benefits:

  • Enables rapid provisioning and tear-down so environments can be ‘on-demand’
  • Ensures consistency between deployments, removes manual error
  • Improves consistency between different environments and reduces ‘configuration drift’
  • Reduces risk by eliminating over-privileged manual access

The use of automation leads to ‘immutable infrastructure’ - where infrastructure is always recreated from a defined set of rules (code) when it is required. Changes are always applied to the defined rules and never to the deployed infrastructure. The opposite of immutable infrastructure are ‘snowflake servers’, where each server is complex and unique.

Infrastructure Deployment PatternsInfrastructure Deployment Patterns

Software Development Patterns

The following diagram is taken from the DORA State of DevOps Report. It depicts the strong causal relationship between certain software development practices and Software Development and Operational (SDO) performance.

 strong causal relationship between certain software development practices and Software Development and Operational (SDO) performance strong causal relationship between certain software development practices and Software Development and Operational (SDO) performance

These practices are fundamental to supporting the continual flow of value in a digital enterprise.

Design for Continuous Operations

In order to provide an exceptional user experience, understanding how your systems behave and proactively addressing issues before they escalate is crucial. Antifragile systems remove the need for fire-fighting, enabling focus on new features and delivering value. Improved feedback loops allow you to understand usage patterns and to ensure you focus on building valuable services.

Monitoring and Observability

Typically on-premise hardware and software assets are tracked via cumbersome methods like a manual “CMDB” and logging and monitoring are an afterthought. With cloud computing much of this comes for free and offers much greater transparency but careful thought must be put into its design, configuration and deployment (generally automated).

Appropriate tools are required for observability, to provide Logging, Monitoring and Tracing to:

  • Measure the Mean Time to Recovery (MTTR) and Mean Time Between Failure (MTBF)
  • Reduce the time for problem identification (MTTI), and problem resolution
  • Enable fault diagnosis, troubleshooting and continuous improvement
  • Satisfy security requirements for logging and auditing

The following targets represent ‘best-of-breed’:

Rules of Thumb

  • Always ensure logs contain sufficient log event data to address the specific requirement
  • Access logs should support both success and failure of specified security events
  • Ensure log entries that include un-trusted data will not execute as code
  • Do not store sensitive information, including session identifiers or passwords
  • Log all apparent tampering events, including unexpected changes to state data
  • Log attempts to connect with invalid or expired session tokens
  • Log all administrative functions, including changes to the security configuration settings
  • Use a cryptographic hash function to validate log entry integrity

Disaster Recovery

Disaster recovery is the process of preparing for and recovering from a disaster. An event that prevents a workload or system from fulfilling its business objectives in its primary deployed location is considered a disaster. The aim is to mitigate risks and meet the Recovery Time Objective (RTO) and Recovery Point Objective (RPO) for a particular workload.

For more detailed insight into disaster recovery in an AWS context read: Disaster Recovery of Workloads on AWS: Recovery in the Cloud Whitepaper.

Recovery Objectives (RTO and RPO)

When creating a Disaster Recovery (DR) strategy, organisations most commonly plan for the Recovery Time Objective (RTO) and Recovery Point Objective (RPO).

Recovery Point Objective (RPO) is the maximum acceptable amount of time since the last data recovery point. This objective determines what is considered an acceptable loss of data between the last recovery point and the interruption of service and is defined by the organization.

Recovery Time Objective (RTO) is the maximum acceptable delay between the interruption of service and restoration of service. This objective determines what is considered an acceptable time window when service is unavailable and is defined by the organization.

Disaster Recovery Patterns in AWS

Disaster recovery strategies available to you within AWS can be broadly categorised into four approaches. For traditional server based applications they represent a spectrum of cost and complexity, but the higher levels are available to modern cloud native solutions at no extra cost.

It is also critical to regularly test your disaster recovery strategy so that you have confidence in invoking it, should it become necessary.

Backup and Restore

Backup and restore is an effective approach for mitigating against data loss or corruption when you have strong IaC practices. Consistent deployment pipelines and immutable infrastructure enable environment recreation in hours.

In the event of a full region failure, services would be unavailable for the duration of the outage. Your workload data will require a backup strategy that runs periodically or continuously and aligns to meet your RPO.

Pilot Light & Warm Standby

These two strategies focus on multi-region failover scenarios whereby resources are standing by in another region to be scaled up in the event of a failure. Strong IaC and DevOps practices will enable environment recreation in the space of hours (pilot light) to minutes (warm standby).

Multi-site active/active

You can run your workload simultaneously in multiple regions as part of a multi-site active/active or hot standby active/passive strategy. Multi-site active/active serves traffic from all regions to which it is deployed, whereas hot standby serves traffic only from a single region, and the other region(s) are only used for disaster recovery.

While multi-site active/active may seem complex and costly, if you architect your system to use distributed scalable services (containers, serverless etc) then it can run in multiple regions simultaneously and will provide the highest levels of resilience and continuity.


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