ScienceSoft’s Approach to Legacy Application Integration

Adding a helper service (proxy) to handle network requests from new applications to the legacy system.

An ambassador service can be thought of as an out-of-process proxy that is co-located with the legacy application. The ambassador focuses on simplifying external communication, improving resilience, and ensuring compatibility. The ambassador pattern is a practical solution for integrating legacy systems into cloud-native environments.

Key use cases:

• Translating data and protocols: adapting legacy data formats or protocols to modern standards, with the proxy acting as a translator between systems.
• Handling errors: enabling resilience with retry logic, circuit breakers, and failover mechanisms.
• Enhancing security: securing outbound API calls and routing them.

Integrating a secondary component alongside the legacy system to add modern functionality while preserving the integrity of the system’s core.

The sidecar pattern deploys an auxiliary service alongside the primary application. The sidecar enhances the app’s internal operations or manages auxiliary tasks like logging, monitoring, security, and data transformation without modifying the legacy system. Running in the same environment (e.g., container or pod), the sidecar communicates directly with the legacy application but can be scaled independently. Sidecars help avoid complex integrations by isolating operational tasks in the sidecar, simplifying overall system management. The sidecar pattern is particularly valuable when integrating legacy systems with containerized or microservices-based environments.

Key use cases:

• Enhancing observability: collecting and analyzing performance metrics and logs for legacy systems that lack robust monitoring tools.
• Improving security: adding modern authentication and authorization mechanisms.
• Transforming data: preprocessing data to ensure compatibility between the legacy system and modern applications, especially when the transformation logic is light or system-specific.
• Enhancing operational resilience and maintainability: handling retries, error management, and configurations outside the legacy application.

Creating a front-facing layer that consolidates multiple legacy interfaces into a single, cohesive API, simplifying access from external services.

External applications interact with the façade without needing to understand or adapt to the complexities of the legacy system. It is particularly effective for organizations aiming to extend the life and functionality of legacy systems while embracing modern application architectures.

Key use cases:

• Simplifying access to legacy systems: creating easy-to-use APIs for data exchange with modern apps.
• Enabling extensibility: the façade serves as a stable access point, allowing new features or enhancements to be introduced within the legacy system without disrupting external consumers or requiring changes to the API.
• Offering developer-friendly interfaces: thanks to simplified, well-documented endpoints.

Adding an intermediary between legacy systems and modern applications, often as a set of APIs or an ESB, to mediate and transform data and functionality.

The ACL serves as a protective barrier that isolates modern applications from the complexities, inconsistencies, and limitations of legacy systems. It transforms data, requests, and workflows to ensure smooth interoperability while protecting modern architectures from outdated domain models or rigid data structures or legacy systems. When paired with API gateways, the ACL also supports authentication, rate limiting, caching, and monitoring, enhancing security and reliability.

Key use cases:

• Complex data transformations: adapting legacy data models, protocols, and workflows for modern applications.
• Progressive modernization of the integrated system: isolating modern systems from legacy dependencies, enabling gradual replacement or enhancement of legacy components without disrupting operations.
• Improving reliability: reducing errors through consistent data transformation and normalization and protocol translation.

Gradually replacing legacy functionality by integrating modern components alongside the old system, which is less risky than a complete system overhaul.

By gradually replacing or refactoring outdated components with modern alternatives while the original system remains operational, strangler fig pattern ensures service continuity and reduces the risks associated with a complete system overhaul. The pattern relies on API gateways and routing, ACL patterns, monitoring and observability components, phased rollouts, and more.

Key use cases:

• Non-disruptive modernization: keeping the legacy modules operational throughout the gradual switch to new systems to avoid service downtime.
• Introducing and validating new components in a controlled manner, which allows for isolating and addressing issues in smaller, manageable steps.
• Spreading modernization costs over time, making it more manageable, and understanding the economic feasibility better.

Using a centralized mechanism to manage and direct traffic between disparate systems, abstracting the complexities of their underlying differences.

The gateway routing pattern introduces a unified entry point for legacy and modern system components. It also balances traffic loads and handles overall security, monitoring, and scaling.

Key use cases:

• Centralized control: managing critical aspects like rate limiting, logging, and monitoring from a single point, simplifying operations.
• Simplifying modernization: gradually transitioning from legacy to modern systems by routing specific requests to new services without disrupting existing workflows.
• Enhancing security: easily enforcing security measures, such as authentication, authorization, and encryption, to protect sensitive data across all systems.

Combining the gradual modernization approach of the strangler fig pattern with the scalability and agility of microservices.

With the strangler + microservices transition pattern, specific legacy functions — such as transactions, invoicing, or reporting — are progressively replaced by independent microservices that replicate and enhance the original functionality, with the legacy system becoming less dependent on over time.

Key use cases:

• Enabling scalability and agility: independently scaling microservices to meet growing demands and adopting new technologies.
• Future-proofing legacy software systems: enabling easier adoption of cloud technologies and cloud-native features.