Idempotency and Concurrency

Idempotency Keys

AWS HealthLake supports idempotency keys for FHIR POST operations, providing a robust mechanism to ensure data integrity during resource creation. By including a unique UUID as an idempotency key in the request header, healthcare applications can guarantee that each FHIR resource is created exactly once, even in scenarios involving network instability or automatic retries.

This feature is particularly crucial for healthcare systems where duplicate medical records could have serious consequences. When a request is received with the same idempotency key as a previous request, HealthLake will return the original resource instead of creating a duplicate. For example, this could occur during a retry loop or due to redundant request pipelines. Using the idempotency key allows HealthLake to maintain data consistency while providing a seamless experience for client applications handling intermittent connectivity issues.

Implementation

POST /<baseURL>/Patient
x-amz-fhir-idempotency-key: 123e4567-e89b-12d3-a456-426614174000
{
    "resourceType": "Patient",
    "name": [...]
}

Response Scenarios

Best Practices

ETag in AWS HealthLake

AWS HealthLake uses ETags for optimistic concurrency control in FHIR resources, providing a reliable mechanism to manage concurrent modifications and maintain data consistency. An ETag is a unique identifier that represents a specific version of a resource, functioning as a version control system through HTTP headers. When reading or modifying resources, applications can use ETags to prevent unintended overwrites and ensure data integrity, particularly in scenarios with potential concurrent updates.

Implementation Example

// Initial Read
GET /fhir/Patient/123
Response: 
ETag: W/"1"

// Update with If-Match
PUT /fhir/Patient/123
If-Match: W/"1"
{resource content}

// Create with If-None-Match
PUT /fhir/Patient/123
If-None-Match: *
{resource content}
// Succeeds only if resource doesn't exist
// Fails with 412 if resource exists

Response Scenarios

Best Practices

This concurrency control system is essential for maintaining the integrity of healthcare data, especially in environments with multiple users or systems accessing and modifying the same resources.