Generalize apollo-server graceful shutdown to all integrations (#5635)

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.
- Remove some examples from READMEs and point to examples in the docs
  instead. Keeping both up to date is extra work.
- 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.

CHANGELOG.md

@@ -9,6 +9,7 @@ The version headers in this history reflect the versions of Apollo Server itself
 
 ## vNEXT
 
+- `apollo-server-core`: Previously, only the batteries-included `apollo-server` package supported a graceful shutdown. Now the integrations support it as well, if you tell your `ApolloServer` which HTTP server to drain with the new `ApolloServerPluginDrainHttpServer` plugin. This plugin implements a new `drainServer` plugin hook. For `apollo-server-hapi` you can use `ApolloServerPluginStopHapiServer` instead. [PR #5635](https://github.com/apollographql/apollo-server/pull/5635)
 - `apollo-server-core`: Fix `experimental_approximateDocumentStoreMiB` option, which seems to have never worked before. [PR #5629](https://github.com/apollographql/apollo-server/pull/5629)
 - `apollo-server-core`: Only register `SIGINT` and `SIGTERM` handlers once the server successfully starts up; trying to call `stop` on a server that hasn't successfully started had undefined behavior. By default, don't register the handlers in serverless integrations, which don't have the same lifecycle as non-serverless integrations (eg, there's no explicit `start` call); you can still explicitly set `stopOnTerminationSignals` to override this default. [PR #5639](https://github.com/apollographql/apollo-server/pull/5639)
 

docs/gatsby-config.js

@@ -77,6 +77,7 @@ module.exports = {
             'api/plugin/usage-reporting',
             'api/plugin/schema-reporting',
             'api/plugin/inline-trace',
+            'api/plugin/drain-http-server',
             'api/plugin/cache-control',
             'api/plugin/landing-pages',
           ],

docs/source/api/apollo-server.md

@@ -517,22 +517,22 @@ The `start` method triggers the following actions:
 
 ## `stop`
 
-`ApolloServer.stop()` is an async method that tells all of Apollo Server's background tasks to complete. It calls and awaits all [`serverWillStop` plugin handlers](../integrations/plugins-event-reference/#serverwillstop) (including the [usage reporting plugin](./plugin/usage-reporting/)'s handler, which sends a final usage report to Apollo Studio). This method takes no arguments. You should only call it after [`start()`](#start) returns successfully (or [`listen()`](#listen) if you're using the batteries-included `apollo-server` package).
+`ApolloServer.stop()` is an async method that tells all of Apollo Server's background tasks to complete. Specifically, it:
 
-If your server is a [federated gateway](https://www.apollographql.com/docs/federation/gateway/), `stop` also stops gateway-specific background activities, such as polling for updated service configuration.
+- Calls and awaits all [`drainServer` plugin handlers](../integrations/plugins-event-reference/#drainserver). These should generally:
+  * Stop listening for new connections
+  * Closes idle connections (i.e., connections with no current HTTP request)
+  * Closes active connections whenever they become idle
+  * Waits for all connections to be closed
+  * After a grace period, if any connections remain active, forcefully close them.
+  If you're using the batteries-included `apollo-server` package, it does this by default. (You can configure the grace period with the [`stopGracePeriodMillis` constructor option](#stopgraceperiodmillis).) Otherwise, you can use the [drain HTTP server plugin](./plugin/drain-http-server/) to drain your HTTP server.
+- Transitions the server to a state where it will not start executing more GraphQL operations.
+- Calls and awaits all [`serverWillStop` plugin handlers](../integrations/plugins-event-reference/#serverwillstop) (including the [usage reporting plugin](./plugin/usage-reporting/)'s handler, which sends a final usage report to Apollo Studio).
+- If your server is a [federated gateway](https://www.apollographql.com/docs/federation/gateway/), `stop` also stops gateway-specific background activities, such as polling for updated service configuration.
 
-In some circumstances, Apollo Server calls `stop` automatically when the process receives a `SIGINT` or `SIGTERM` signal. See the [`stopOnTerminationSignals` constructor option](#stoponterminationsignals) for details.
-
-If you're using the `apollo-server` package (which handles setting up an HTTP server for you), this method first stops the HTTP server. Specifically, it:
-
-* Stops listening for new connections
-* Closes idle connections (i.e., connections with no current HTTP request)
-* Closes active connections whenever they become idle
-* Waits for all connections to be closed
-
-If any connections remain active after a grace period (10 seconds by default), Apollo Server forcefully closes those connections. You can configure this grace period with the [`stopGracePeriodMillis` constructor option](#stopgraceperiodmillis).
+This method takes no arguments. You should only call it after [`start()`](#start) returns successfully (or [`listen()`](#listen) if you're using the batteries-included `apollo-server` package).
 
-If you're using a [middleware package](../integrations/middleware/) instead of `apollo-server`, you should stop your HTTP server before calling `ApolloServer.stop()`.
+In some circumstances, Apollo Server calls `stop` automatically when the process receives a `SIGINT` or `SIGTERM` signal. See the [`stopOnTerminationSignals` constructor option](#stoponterminationsignals) for details.
 
 ## Framework-specific middleware function
 
@@ -547,23 +547,25 @@ These functions take an `options` object as a parameter. Some supported fields o
 ```js
 const express = require('express');
 const { ApolloServer } = require('apollo-server-express');
+const { ApolloServerPluginDrainHttpServer } = require('apollo-server-core');
 const { typeDefs, resolvers } = require('./schema');
 
 async function startApolloServer() {
+  const app = express();
+  const httpServer = http.createServer(app);
   const server = new ApolloServer({
     typeDefs,
     resolvers,
+    plugins: [ApolloServerPluginDrainHttpServer({ httpServer })],
   });
   await server.start();
 
-  const app = express();
-
   // Additional middleware can be mounted at this point to run before Apollo.
   app.use('*', jwtCheck, requireAuth, checkScope);
 
   // Mount Apollo middleware here.
   server.applyMiddleware({ app, path: '/specialUrl' });
-  await new Promise(resolve => app.listen({ port: 4000 }, resolve));
+  await new Promise(resolve => httpServer.listen({ port: 4000 }, resolve));
   console.log(`🚀 Server ready at http://localhost:4000${server.graphqlPath}`);
   return { server, app };
 }

docs/source/api/plugin/drain-http-server.md

@@ -0,0 +1,90 @@
+---
+title: "API Reference: Drain HTTP server plugin"
+sidebar_title: Drain HTTP server
+api_reference: true
+---
+
+## Using the plugin
+
+This API reference documents the `ApolloServerPluginDrainHttpServer` plugin.
+
+This plugin is designed for use with [`apollo-server-express` and other framework-specific packages](../../integrations/middleware/#all-supported-packages) which are built on top of [Node `http.Server`s](https://nodejs.org/api/http.html#http_class_http_server). It is highly recommended that you use this plugin with packages like `apollo-server-express` if you want your server to shut down gracefully.
+
+You do not need to explicitly use this plugin with the batteries-included `apollo-server` package: that package automatically uses this plugin internally.
+
+When you use this plugin, Apollo Server will drain your HTTP server when you call the `stop()` method (which is also called for you when the `SIGTERM` and `SIGINT` signals are received, unless disabled with the [`stopOnTerminationSignals` constructor option](../apollo-server/#stoponterminationsignals)). Specifically, it will:
+
+* Stop listening for new connections
+* Close idle connections (i.e., connections with no current HTTP request)
+* Close active connections whenever they become idle
+* Wait for all connections to be closed
+* After a grace period, if any connections remain active, forcefully close them.
+
+This plugin is exported from the `apollo-server-core` package. It is tested with `apollo-server-express`, `apollo-server-koa`, and `apollo-server-fastify`. (If you're using Hapi, you should instead use the `ApolloServerPluginStopHapiServer` plugin exported from the `apollo-server-hapi` package.)
+
+Here's a basic example of how to use it with Express. See the [framework integrations docs](../../integrations/middleware/) for examples of how to use it with other frameworks.
+
+```js
+const express = require('express');
+const { ApolloServer } = require('apollo-server-express');
+const { ApolloServerPluginDrainHttpServer } = require('apollo-server-core');
+const { typeDefs, resolvers } = require('./schema');
+
+async function startApolloServer() {
+  const app = express();
+  const httpServer = http.createServer(app);
+  const server = new ApolloServer({
+    typeDefs,
+    resolvers,
+    plugins: [ApolloServerPluginDrainHttpServer({ httpServer })],
+  });
+  await server.start();
+
+  // Mount Apollo middleware here.
+  server.applyMiddleware({ app });
+  await new Promise(resolve => httpServer.listen({ port: 4000 }, resolve));
+  console.log(`🚀 Server ready at http://localhost:4000${server.graphqlPath}`);
+  return { server, app };
+}
+```
+
+## Options
+
+<table class="field-table">
+  <thead>
+    <tr>
+      <th>Name /<br/>Type</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+
+<tbody>
+
+<tr>
+<td>
+
+###### `httpServer`
+
+[`http.Server`](https://nodejs.org/api/http.html#http_class_http_server)
+</td>
+<td>
+
+The server to drain; required.
+</td>
+</tr>
+
+<tr>
+<td>
+
+###### `stopGracePeriodMillis`
+
+`number`
+</td>
+<td>
+
+How long to wait before forcefully closing non-idle connections. Defaults to `10_000` (ten seconds).
+</td>
+</tr>
+
+</tbody>
+</table>

docs/source/data/subscriptions.mdx

@@ -99,16 +99,26 @@ To run both an Express app _and_ a separate subscription server, we'll create an
        // This `server` is the instance returned from `new ApolloServer`.
        path: server.graphqlPath,
     });
+    ```
 
-    // Shut down in the case of interrupt and termination signals
-    // We expect to handle this more cleanly in the future. See (#5074)[https://github.com/apollographql/apollo-server/issues/5074] for reference.
-    ['SIGINT', 'SIGTERM'].forEach(signal => {
-      process.on(signal, () => subscriptionServer.close());
-    });
+6. Add a plugin to your `ApolloServer` constructor to close the `SubscriptionServer`.
 
+    ```javascript:title=index.js
+    const server = new ApolloServer({
+      schema,
+      plugins: [{
+        async serverWillStart() {
+          return {
+            async drainServer() {
+              subscriptionServer.close();
+            }
+          };
+        }
+      }],
+    });
     ```
 
-6. Finally, we need to adjust our existing `listen` call.
+7. Finally, we need to adjust our existing `listen` call.
 
     Most Express applications call `app.listen(...)`. **Change this to `httpServer.listen(...)`** with the same arguments. This way, the server starts listening on the HTTP and WebSocket transports simultaneously.
 
@@ -136,17 +146,26 @@ import typeDefs from "./typeDefs";
     resolvers,
   });
 
+  const subscriptionServer = SubscriptionServer.create(
+    { schema, execute, subscribe },
+    { server: httpServer, path: server.graphqlPath }
+  );
+
   const server = new ApolloServer({
     schema,
+    plugins: [{
+      async serverWillStart() {
+        return {
+          async drainServer() {
+            subscriptionServer.close();
+          }
+        };
+      }
+    }],
   });
   await server.start();
   server.applyMiddleware({ app });
 
-  SubscriptionServer.create(
-    { schema, execute, subscribe },
-    { server: httpServer, path: server.graphqlPath }
-  );
-
   const PORT = 4000;
   httpServer.listen(PORT, () =>
     console.log(`Server is now running on http://localhost:${PORT}/graphql`)