lambda: Implement onHealthCheck on createHandler. (#3458)

CHANGELOG.md

@@ -7,6 +7,7 @@ The version headers in this history reflect the versions of Apollo Server itself
 > The changes noted within this `vNEXT` section have not been released yet.  New PRs and commits which introduce changes should include an entry in this `vNEXT` section as part of their development.  When a release is being prepared, a new header will be (manually) created below and the the appropriate changes within that release will be moved into the new section.
 
 - `apollo-server-core`: Don't try parsing `variables` and `extensions` as JSON if they are defined but empty strings. [PR #3501](https://github.com/apollographql/apollo-server/pull/3501)
+- `apollo-server-lambda`: Introduce `onHealthCheck` on `createHandler` in the same fashion as implemented in other integrations. [PR #3458](https://github.com/apollographql/apollo-server/pull/3458)
 
 ### v2.9.8
 

packages/apollo-server-lambda/src/ApolloServer.ts

@@ -21,6 +21,7 @@ export interface CreateHandlerOptions {
     credentials?: boolean;
     maxAge?: number;
   };
+  onHealthCheck?: (req: APIGatewayProxyEvent) => Promise<any>;
 }
 
 export class ApolloServer extends ApolloServerBase {
@@ -47,7 +48,7 @@ export class ApolloServer extends ApolloServerBase {
     return super.graphQLServerOptions({ event, context });
   }
 
-  public createHandler({ cors }: CreateHandlerOptions = { cors: undefined }) {
+  public createHandler({ cors, onHealthCheck }: CreateHandlerOptions = { cors: undefined, onHealthCheck: undefined }) {
     // We will kick off the `willStart` event once for the server, and then
     // await it before processing any requests by incorporating its `await` into
     // the GraphQLServerOptions function which is called before each request.
@@ -159,6 +160,35 @@ export class ApolloServer extends ApolloServerBase {
         });
       }
 
+      if (event.path === '/.well-known/apollo/server-health') {
+        const successfulResponse = {
+          body: JSON.stringify({ status: 'pass' }),
+          statusCode: 200,
+          headers: {
+            'Content-Type': 'application/json',
+            ...requestCorsHeadersObject,
+          },
+        };
+        if (onHealthCheck) {
+          onHealthCheck(event)
+            .then(() => {
+              return callback(null, successfulResponse);
+            })
+            .catch(() => {
+              return callback(null, {
+                body: JSON.stringify({ status: 'fail' }),
+                statusCode: 503,
+                headers: {
+                  'Content-Type': 'application/json',
+                  ...requestCorsHeadersObject,
+                },
+              });
+            });
+          } else {
+            return callback(null, successfulResponse);
+          }
+      }
+
       if (this.playgroundOptions && event.httpMethod === 'GET') {
         const acceptHeader = event.headers['Accept'] || event.headers['accept'];
         if (acceptHeader && acceptHeader.includes('text/html')) {