feat: allow async creation of FhirConfig (#464)

src/config.ts

@@ -72,7 +72,7 @@ const OAuthUrl =
         ? 'https://OAUTH2.com'
         : process.env.OAUTH2_DOMAIN_ENDPOINT;
 
-export const fhirConfig: FhirConfig = {
+export const getFhirConfig = async (): Promise<FhirConfig> => ({
     configVersion: 1.0,
     productInfo: {
         orgName: 'Organization Name',
@@ -131,6 +131,6 @@ export const fhirConfig: FhirConfig = {
               tenantIdClaimPath: 'custom:tenantId',
           }
         : undefined,
-};
+});
 
 export const genericResources = baseResources;

src/index.ts

@@ -5,14 +5,30 @@
 
 import serverless from 'serverless-http';
 import { generateServerlessRouter } from 'fhir-works-on-aws-routing';
-import { fhirConfig, genericResources } from './config';
+import { getFhirConfig, genericResources } from './config';
 
-const serverlessHandler = serverless(generateServerlessRouter(fhirConfig, genericResources), {
-    request(request: any, event: any) {
-        request.user = event.user;
-    },
-});
+const ensureAsyncInit = async (initPromise: Promise<any>): Promise<void> => {
+    try {
+        await initPromise;
+    } catch (e) {
+        console.error('Async initialization failed', e);
+        // Explicitly exit the process so that next invocation re-runs the init code.
+        // This prevents Lambda containers from caching a rejected init promise
+        process.exit(1);
+    }
+};
+
+async function asyncServerless() {
+    return serverless(generateServerlessRouter(await getFhirConfig(), genericResources), {
+        request(request: any, event: any) {
+            request.user = event.user;
+        },
+    });
+}
+
+const serverlessHandler: Promise<any> = asyncServerless();
 
 export default async (event: any = {}, context: any = {}): Promise<any> => {
-    return serverlessHandler(event, context);
+    await ensureAsyncInit(serverlessHandler);
+    return (await serverlessHandler)(event, context);
 };