Comparing SOAP Migration Strategies: API Gateways vs. GraphQL Middleware vs. Simple Code Approaches

Introduction

Migrating a legacy SOAP-based system to REST involves multiple strategies, each with distinct advantages and trade-offs. The approaches we’ve previously discussed include:

1. Simple Code-Based Approaches – Writing custom wrappers and manual conversions.
2. GraphQL as Middleware – Providing an abstraction layer while gradually migrating to REST.
3. Deploying an API Gateway – Routing requests dynamically to SOAP or REST endpoints.

In this article, we’ll compare API Gateway solutions (Kong, Apigee, AWS API Gateway) with the other migration strategies. We’ll discuss the history, cost, implementation complexity, and ideal use cases for each approach.

Understanding API Gateways

An API Gateway acts as a reverse proxy that routes client requests to different backend services based on rules. This means that during migration, the gateway can send some requests to SOAP and some to REST, enabling a smooth transition.

Popular API Gateways

How API Gateways Handle SOAP to REST Migration

• SOAP endpoints are proxied via the API Gateway.
• Requests are rewritten dynamically (e.g., transforming JSON REST calls into SOAP XML).
• Rate limiting, caching, and authentication are handled at the gateway level.

Example: Kong Gateway Config for SOAP to REST Routing

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services:
  - name: legacy-soap-service
    url: http://soap-backend.example.com
    routes:
      - name: soap-route
        paths:
          - /api/v1/users
          - /api/v1/orders

Comparing Approaches: API Gateway vs. GraphQL vs. Simple Code

1. Simple Code-Based Approach

Description: Writing custom scripts or middleware to translate REST calls into SOAP requests.

• Pros: Fully customizable, no dependency on external services.
• Cons: High development effort, requires ongoing maintenance.

Example:

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import requests

def get_user(user_id):
    soap_request = f"""
    <GetUserRequest>
       <userId>{user_id}</userId>
    </GetUserRequest>
    """
    response = requests.post("http://legacy-soap-service", data=soap_request)
    return response.text

2. GraphQL as Middleware

Description: GraphQL sits between the client and the backend, abstracting SOAP and REST differences.

• Pros: Flexible queries, allows gradual migration.
• Cons: Adds complexity, requires GraphQL infrastructure.

Example:

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type Query {
  getUser(id: ID!): User
}

type User {
  id: ID!
  name: String
}

3. API Gateway Approach

Description: An API Gateway dynamically routes requests to SOAP or REST, handling protocol transformations.

• Pros: No code changes, centralized API management.
• Cons: Potential vendor lock-in, cost of managed solutions.

Example: AWS API Gateway SOAP Integration:

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{
  "type": "AWS",
  "httpMethod": "POST",
  "uri": "https://legacy-soap-endpoint.com",
  "requestTemplates": {
    "application/json": "{ \"GetUserRequest\": { \"userId\": $input.params('id') } }"
  }
}

Cost & Complexity Comparison

When to Use Each Approach

Use API Gateway When:

• You want to avoid modifying existing services.
• You need centralized API management (authentication, caching, rate limiting).
• You prefer low-maintenance solutions.

Use GraphQL Middleware When:

• Your application requires flexible data queries.
• You’re gradually replacing SOAP with REST.
• You want to abstract backend differences.

Use Simple Code When:

• Your team has strong development expertise.
• You need full control over the migration process.
• You prefer lightweight, dependency-free solutions.

Conclusion

Choosing between API Gateways, GraphQL Middleware, and Simple Code Approaches depends on cost, complexity, and long-term maintenance needs.

• API Gateway is the best choice for enterprise-level projects that need centralized control and minimal changes to legacy services.
• GraphQL Middleware is ideal for teams that need flexibility and incremental migration.
• Simple Code Approaches work well for small teams that want full customization without external dependencies.

By understanding the trade-offs of each approach, teams can choose the right migration path that balances cost, effort, and future scalability.

References

• Kong API Gateway
• Google Apigee
• AWS API Gateway
• GraphQL vs REST