Generalize apollo-server graceful shutdown to all integrations

Previously, the batteries-included `apollo-server` package had a special
override of `stop()` which drains the HTTP server before letting the
actual Apollo Server `stop()` machinery begin. This meant that
`apollo-server` followed this nice shutdown lifecycle:
- Stop listening for new connections
- Close all idle connections and start closing connections as they go
  idle
- Wait a grace period for all connections to close and force-close any
  remaining ones
- Transition ApolloServer to the stopping state, where no operations
  will run
- Run stop hooks (eg send final usage report)

This was great... but only `apollo-server` worked this way, because only
`apollo-server` has full knowledge and control over its HTTP server.

This PR adds a server draining step to the ApolloServer lifecycle and
plugin interface, and provides a built-in plugin which drains a Node
`http.Server` using the logic of the first three steps above.
`apollo-server`'s behavior is now just to automatically install the
plugin.

Specifically:
- Add a new 'phase' called `draining` that fits between `started` and
  `stopping`. Like `started`, operations can still execute during
  `draining`. Like `stopping`, any concurrent call to `stop()` will just
  block until the first `stop()` call finishes rather than starting a
  second shutdown process.
- Add a new `drainServer` plugin hook (on the object returned by
  `serverWillStart`). Invoke all `drainServer` hooks in parallel during
  the `draining` phase.
- Make calling `stop()` when `start()` has not yet completed
  successfully into an error. That behavior was previously undefined.
  Note that as of #5639, the automatic `stop()` call from signal
  handlers can't happen before `start()` succeeds.
- Add `ApolloServerPluginDrainHttpServer` to `apollo-server-core`.
  This plugin implements `drainServer` using the `Stopper` class
  that was previously in the `apollo-server` package. The default
  grace period is 10 seconds.
- Clean up integration tests to just use `stop()` with the plugin
  instead of separately stopping the HTTP server. Note that for Fastify
  specifically we also call `app.close` although there is some weirdness
  here around both `app.close` and our Stopper closing the same server.
  A comment describes the weirdness; perhaps Fastify experts can improve
  this later.
- The Hapi web framework has built in logic that is similar to our
  Stopper, so `apollo-server-hapi` exports
  `ApolloServerPluginStopHapiServer` which should be used instead of the
  other plugin with Hapi.
- Fix some test issues (eg, have FakeTimers only mock out Date.now
  instead of setImmediate, drop an erroneous `const` which made an `app`
  not get cleaned up, etc).

Fixes #5074.

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

@@ -80,19 +80,36 @@ export type SchemaDerivedData = {
 };
 
 type ServerState =
-  | { phase: 'initialized'; schemaManager: SchemaManager }
+  | {
+      phase: 'initialized';
+      schemaManager: SchemaManager;
+    }
   | {
       phase: 'starting';
       barrier: Resolvable<void>;
       schemaManager: SchemaManager;
     }
-  | { phase: 'failed to start'; error: Error }
+  | {
+      phase: 'failed to start';
+      error: Error;
+    }
   | {
       phase: 'started';
       schemaManager: SchemaManager;
     }
-  | { phase: 'stopping'; barrier: Resolvable<void> }
-  | { phase: 'stopped'; stopError: Error | null };
+  | {
+      phase: 'draining';
+      schemaManager: SchemaManager;
+      barrier: Resolvable<void>;
+    }
+  | {
+      phase: 'stopping';
+      barrier: Resolvable<void>;
+    }
+  | {
+      phase: 'stopped';
+      stopError: Error | null;
+    };
 
 // Throw this in places that should be unreachable (because all other cases have
 // been handled, reducing the type of the argument to `never`). TypeScript will
@@ -121,6 +138,7 @@ export class ApolloServerBase<
   private state: ServerState;
   private toDispose = new Set<() => Promise<void>>();
   private toDisposeLast = new Set<() => Promise<void>>();
+  private drainServers: (() => Promise<void>) | null = null;
   private experimental_approximateDocumentStoreMiB: Config['experimental_approximateDocumentStoreMiB'];
   private stopOnTerminationSignals: boolean;
   private landingPage: LandingPage | null = null;
@@ -137,13 +155,15 @@ export class ApolloServerBase<
       typeDefs,
       parseOptions = {},
       introspection,
-      mocks,
-      mockEntireSchema,
       plugins,
       gateway,
-      experimental_approximateDocumentStoreMiB,
-      stopOnTerminationSignals,
       apollo,
+      stopOnTerminationSignals,
+      // These next options aren't used in this function but they don't belong in
+      // requestOptions.
+      mocks,
+      mockEntireSchema,
+      experimental_approximateDocumentStoreMiB,
       ...requestOptions
     } = config;
 
@@ -425,6 +445,17 @@ export class ApolloServerBase<
         });
       }
 
+      const drainServerCallbacks = taggedServerListeners.flatMap((l) =>
+        l.serverListener.drainServer ? [l.serverListener.drainServer] : [],
+      );
+      if (drainServerCallbacks.length) {
+        this.drainServers = async () => {
+          await Promise.all(
+            drainServerCallbacks.map((drainServer) => drainServer()),
+          );
+        };
+      }
+
       // Find the renderLandingPage callback, if one is provided. If the user
       // installed ApolloServerPluginLandingPageDisabled then there may be none
       // found. On the other hand, if the user installed a landingPage plugin,
@@ -537,6 +568,7 @@ export class ApolloServerBase<
             'This data graph is missing a valid configuration. More details may be available in the server logs.',
           );
         case 'started':
+        case 'draining': // We continue to run operations while draining.
           return this.state.schemaManager.getSchemaDerivedData();
         case 'stopping':
           throw new Error(
@@ -559,7 +591,7 @@ export class ApolloServerBase<
   }
 
   protected assertStarted(methodName: string) {
-    if (this.state.phase !== 'started') {
+    if (this.state.phase !== 'started' && this.state.phase !== 'draining') {
       throw new Error(
         'You must `await server.start()` before calling `server.' +
           methodName +
@@ -648,45 +680,67 @@ export class ApolloServerBase<
     };
   }
 
-  /**
-   * XXX: Note that stop() was designed to be called after start() has finished,
-   * and should not be called concurrently with start() or before start(), or
-   * else unexpected behavior may occur (e.g. some dependencies may not be
-   * stopped).
-   */
   public async stop() {
-    // Calling stop more than once should have the same result as the first time.
-    if (this.state.phase === 'stopped') {
-      if (this.state.stopError) {
-        throw this.state.stopError;
-      }
-      return;
-    }
+    switch (this.state.phase) {
+      case 'initialized':
+      case 'starting':
+      case 'failed to start':
+        throw Error(
+          'apolloServer.stop() should only be called after `await apolloServer.start()` has succeeded',
+        );
 
-    // Two parallel calls to stop; just wait for the other one to finish and
-    // do whatever it did.
-    if (this.state.phase === 'stopping') {
-      await this.state.barrier;
-      // The cast here is because TS doesn't understand that this.state can
-      // change during the await
-      // (https://github.com/microsoft/TypeScript/issues/9998).
-      const state = this.state as ServerState;
-      if (state.phase !== 'stopped') {
-        throw Error(`Surprising post-stopping state ${state.phase}`);
-      }
-      if (state.stopError) {
-        throw state.stopError;
+      // Calling stop more than once should have the same result as the first time.
+      case 'stopped':
+        if (this.state.stopError) {
+          throw this.state.stopError;
+        }
+        return;
+
+      // Two parallel calls to stop; just wait for the other one to finish and
+      // do whatever it did.
+      case 'stopping':
+      case 'draining': {
+        await this.state.barrier;
+        // The cast here is because TS doesn't understand that this.state can
+        // change during the await
+        // (https://github.com/microsoft/TypeScript/issues/9998).
+        const state = this.state as ServerState;
+        if (state.phase !== 'stopped') {
+          throw Error(`Surprising post-stopping state ${state.phase}`);
+        }
+        if (state.stopError) {
+          throw state.stopError;
+        }
+        return;
       }
-      return;
+
+      case 'started':
+        // This is handled by the rest of the function.
+        break;
+
+      default:
+        throw new UnreachableCaseError(this.state);
     }
 
-    // Commit to stopping, actually stop, and update the phase.
+    const barrier = resolvable();
+
+    // Commit to stopping and start draining servers.
+    this.state = {
+      phase: 'draining',
+      schemaManager: this.state.schemaManager,
+      barrier,
+    };
+
+    await this.drainServers?.();
+
+    // Servers are drained. Prevent further operations from starting and call
+    // stop handlers.
     this.state = { phase: 'stopping', barrier: resolvable() };
     try {
       // We run shutdown handlers in two phases because we don't want to turn
-      // off our signal listeners until we've done the important parts of shutdown
-      // like running serverWillStop handlers. (We can make this more generic later
-      // if it's helpful.)
+      // off our signal listeners (ie, allow signals to kill the process) until
+      // we've done the important parts of shutdown like running serverWillStop
+      // handlers. (We can make this more generic later if it's helpful.)
       await Promise.all([...this.toDispose].map((dispose) => dispose()));
       await Promise.all([...this.toDisposeLast].map((dispose) => dispose()));
     } catch (stopError) {

packages/apollo-server-core/src/__tests__/ApolloServerBase.test.ts

@@ -49,16 +49,17 @@ describe('ApolloServerBase construction', () => {
       warn,
       error: jest.fn(),
     };
-    expect(() =>
-      new ApolloServerBase({
-        typeDefs,
-        resolvers,
-        apollo: {
-          graphVariant: 'foo',
-          key: 'service:real:key',
-        },
-        logger,
-      }).stop(),
+    expect(
+      () =>
+        new ApolloServerBase({
+          typeDefs,
+          resolvers,
+          apollo: {
+            graphVariant: 'foo',
+            key: 'service:real:key',
+          },
+          logger,
+        }),
     ).not.toThrow();
     expect(warn).toHaveBeenCalledTimes(1);
     expect(warn.mock.calls[0][0]).toMatch(

packages/apollo-server/src/__tests__/stoppable/server.js → packages/apollo-server-core/src/plugin/drainHttpServer/__tests__/stoppable/server.js

@@ -1,5 +1,7 @@
 const http = require('http');
-const { Stopper } = require('../../../dist/stoppable.js');
+const {
+  Stopper,
+} = require('../../../../../dist/plugin/drainHttpServer/stoppable.js');
 
 const grace = Number(process.argv[2] || Infinity);
 let stopper;

packages/apollo-server-core/src/plugin/drainHttpServer/index.ts

@@ -0,0 +1,26 @@
+import type http from 'http';
+import type { ApolloServerPlugin } from 'apollo-server-plugin-base';
+import { Stopper } from './stoppable';
+
+// FIXME docs in code
+// FIXME write docs
+export interface ApolloServerPluginDrainHttpServerOptions {
+  httpServer: http.Server;
+  // Defaults to 10_000
+  stopGracePeriodMillis?: number;
+}
+
+export function ApolloServerPluginDrainHttpServer(
+  options: ApolloServerPluginDrainHttpServerOptions,
+): ApolloServerPlugin {
+  const stopper = new Stopper(options.httpServer);
+  return {
+    async serverWillStart() {
+      return {
+        async drainServer() {
+          await stopper.stop(options.stopGracePeriodMillis ?? 10_000);
+        },
+      };
+    },
+  };
+}

packages/apollo-server-core/src/plugin/index.ts

@@ -80,6 +80,18 @@ export function ApolloServerPluginCacheControlDisabled(): ApolloServerPlugin {
 }
 //#endregion
 
+//#region Drain HTTP server
+import type { ApolloServerPluginDrainHttpServerOptions } from './drainHttpServer';
+export type { ApolloServerPluginDrainHttpServerOptions } from './drainHttpServer';
+export function ApolloServerPluginDrainHttpServer(
+  options: ApolloServerPluginDrainHttpServerOptions,
+): ApolloServerPlugin {
+  return require('./drainHttpServer').ApolloServerPluginDrainHttpServer(
+    options,
+  );
+}
+//#endregion
+
 //#region LandingPage
 import type { InternalApolloServerPlugin } from '../internalPlugin';
 export function ApolloServerPluginLandingPageDisabled(): ApolloServerPlugin {

packages/apollo-server-express/src/__tests__/ApolloServer.test.ts

@@ -8,6 +8,7 @@ import {
   gql,
   AuthenticationError,
   ApolloServerPluginCacheControlDisabled,
+  ApolloServerPluginDrainHttpServer,
 } from 'apollo-server-core';
 import {
   ApolloServer,
@@ -34,24 +35,34 @@ const resolvers = {
 };
 
 describe('apollo-server-express', () => {
-  let server: ApolloServer;
-  let httpServer: http.Server;
+  let serverToCleanUp: ApolloServer | null = null;
   testApolloServer(
     async (config: ApolloServerExpressConfig, options) => {
-      server = new ApolloServer(config);
+      serverToCleanUp = null;
+      const app = express();
+      const httpServer = http.createServer(app);
+      const server = new ApolloServer({
+        ...config,
+        plugins: [
+          ...(config.plugins ?? []),
+          ApolloServerPluginDrainHttpServer({
+            httpServer: httpServer,
+          }),
+        ],
+      });
       if (!options?.suppressStartCall) {
         await server.start();
+        serverToCleanUp = server;
       }
-      const app = express();
       server.applyMiddleware({ app, path: options?.graphqlPath });
-      httpServer = await new Promise<http.Server>((resolve) => {
-        const s: http.Server = app.listen({ port: 0 }, () => resolve(s));
+      await new Promise((resolve) => {
+        httpServer.once('listening', resolve);
+        httpServer.listen({ port: 0 });
       });
       return createServerInfo(server, httpServer);
     },
     async () => {
-      if (httpServer?.listening) await httpServer.close();
-      if (server) await server.stop();
+      await serverToCleanUp?.stop();
     },
   );
 });

packages/apollo-server-express/src/__tests__/expressApollo.test.ts

@@ -5,17 +5,6 @@ import testSuite, {
   CreateAppOptions,
 } from 'apollo-server-integration-testsuite';
 
-async function createApp(options: CreateAppOptions = {}) {
-  const app = express();
-
-  const server = new ApolloServer(
-    (options.graphqlOptions as ApolloServerExpressConfig) || { schema: Schema },
-  );
-  await server.start();
-  server.applyMiddleware({ app });
-  return app;
-}
-
 describe('expressApollo', () => {
   it('throws error if called without schema', function () {
     expect(() => new ApolloServer(undefined as any)).toThrow(
@@ -25,5 +14,23 @@ describe('expressApollo', () => {
 });
 
 describe('integration:Express', () => {
-  testSuite({ createApp });
+  let serverToCleanUp: ApolloServer | null = null;
+  testSuite({
+    createApp: async function createApp(options: CreateAppOptions = {}) {
+      serverToCleanUp = null;
+      const app = express();
+      const server = new ApolloServer(
+        (options.graphqlOptions as ApolloServerExpressConfig) || {
+          schema: Schema,
+        },
+      );
+      await server.start();
+      serverToCleanUp = server;
+      server.applyMiddleware({ app });
+      return app;
+    },
+    destroyApp: async function () {
+      await serverToCleanUp?.stop();
+    },
+  });
 });