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生产环境下的 Service Worker

Service worker in production

本页讲的是如何使用 Angular Service Worker 发布和支持生产环境下的应用。 它解释了 Angular Service Worker 如何满足大规模生产环境的需求、Service Worker 在多种条件下有哪些行为以及有哪些可用的资源和故障保护机制。

This page is a reference for deploying and supporting production apps that use the Angular service worker. It explains how the Angular service worker fits into the larger production environment, the service worker's behavior under various conditions, and available recourses and fail-safes.

前提条件

Prerequisites

对下列知识有基本的了解:

A basic understanding of the following:


Service Worker 与应用资源的缓存

Service worker and caching of app resources

从概念上说,你可以把 Angular Service Worker 想象成一个转发式缓存或装在最终用户浏览器中的 CDN 边缘。 Service Worker 的工作是从本地缓存中满足 Angular 应用对资源或数据的请求,而不用等待网络。 和所有缓存一样,它有一些规则来决定内容该如何过期或更新。

Conceptually, you can imagine the Angular service worker as a forward cache or a CDN edge that is installed in the end user's web browser. The service worker's job is to satisfy requests made by the Angular app for resources or data from a local cache, without needing to wait for the network. Like any cache, it has rules for how content is expired and updated.

应用的版本

App versions

在 Angular Service Worker 的语境下,“版本”是指用来表示 Angular 应用的某一次构建成果的一组资源。 当应用的一个新的构建发布时,Service Worker 就把它看做此应用的一个新版本。 就算只修改了一个文件,也同样如此。 在任何一个给定的时间,Service Worker 可能会在它的缓存中拥有此应用的多个版本,这几个版本也都能用于提供服务。 要了解更多,参见稍后的 App 选项卡

In the context of an Angular service worker, a "version" is a collection of resources that represent a specific build of the Angular app. Whenever a new build of the app is deployed, the service worker treats that build as a new version of the app. This is true even if only a single file is updated. At any given time, the service worker may have multiple versions of the app in its cache and it may be serving them simultaneously. For more information, see the App tabs section below.

要保持应用的整体性,Angular Service Worker 会用所有的文件共同组成一个版本。 组成版本的这些文件通常包括 HTML、JS 和 CSS 文件。把这些文件分成一组是至关重要的,因为它们会互相引用,并且依赖于一些特定内容。 比如,index.html 文件可能有个引用 bundle.js<script> 标签,它可能会试图从这个脚本中调用一个 startApp() 函数。 任何时候,只要这个版本的 index.html 被提供了,与它对应的 bundle.js 也必须同时提供。 这种情况下,使用调用了 startApp() 的老的 index.html 并同时使用定义了 runApp() 的新 bundle 就是无效的。

To preserve app integrity, the Angular service worker groups all files into a version together. The files grouped into a version usually include HTML, JS, and CSS files. Grouping of these files is essential for integrity because HTML, JS, and CSS files frequently refer to each other and depend on specific content. For example, an index.html file might have a <script> tag that references bundle.js and it might attempt to call a function startApp() from within that script. Any time this version of index.html is served, the corresponding bundle.js must be served with it. For example, assume that the startApp() function is renamed to runApp() in both files. In this scenario, it is not valid to serve the old index.html, which calls startApp(), along with the new bundle, which defines runApp().

当使用惰性加载模块时,文件的整体性就显得格外重要。 某个 JS 包可能引用很多惰性块,而这些惰性块的文件名在应用的每次特定的构建中都是唯一的。 如果运行应用的 X 版本视图加载一个惰性块,但该块的服务器已经升级到了 X + 1版本,这次惰性加载操作就会失败。

This file integrity is especially important when lazy loading modules. A JS bundle may reference many lazy chunks, and the filenames of the lazy chunks are unique to the particular build of the app. If a running app at version X attempts to load a lazy chunk, but the server has updated to version X + 1 already, the lazy loading operation will fail.

本应用的版本标识符由其所有资源的内容决定,如果它们中的任何一个发生了变化,则版本标识符也随之改变。 实际上,版本是由 ngsw.json 文件的内容决定的,包含了所有已知内容的哈希值。 如果任何一个被缓存的文件发生了变化,则该文件的哈希也将在ngsw.json中随之变化,从而导致 Angular Service Worker 将这个活动文件的集合视为一个新版本。

The version identifier of the app is determined by the contents of all resources, and it changes if any of them change. In practice, the version is determined by the contents of the ngsw.json file, which includes hashes for all known content. If any of the cached files change, the file's hash will change in ngsw.json, causing the Angular service worker to treat the active set of files as a new version.

借助 Angular Service Worker 的这种版本控制行为,应用服务器就可以确保这个 Angular 应用中的这组文件始终保持一致。

With the versioning behavior of the Angular service worker, an application server can ensure that the Angular app always has a consistent set of files.

更新检测

Update checks

每当用户打开或刷新应用程序时,Angular Service Worker 都会通过查看清单(manifest)文件 “ngsw.json” 的更新来检查该应用程序的更新。 如果它找到了更新,就会自动下载并缓存这个版本,并在下次加载应用程序时提供。

Every time the user opens or refreshes the application, the Angular service worker checks for updates to the app by looking for updates to the ngsw.json manifest. If an update is found, it is downloaded and cached automatically, and will be served the next time the application is loaded.

资源整体性

Resource integrity

长周期缓存的潜在副作用之一就是可能无意中缓存了无效的资源。 在普通的HTTP缓存中,硬刷新或缓存过期限制了缓存这种无效文件导致的负面影响。 而 Service Worker 会忽略这样的约束,事实上会对整个应用程序进行长期缓存。 因此,让 Service Worker 获得正确的内容就显得至关重要。

One of the potential side effects of long caching is inadvertently caching an invalid resource. In a normal HTTP cache, a hard refresh or cache expiration limits the negative effects of caching an invalid file. A service worker ignores such constraints and effectively long caches the entire app. Consequently, it is essential that the service worker gets the correct content.

为了确保资源的整体性,Angular Service Worker 会验证所有带哈希的资源的哈希值。 通常,对于 Angular CLI 应用程序,用户的 src/ngsw-config.json 配置文件中会涵盖 dist 目录下的所有内容。

To ensure resource integrity, the Angular service worker validates the hashes of all resources for which it has a hash. Typically for an app created with the Angular CLI, this is everything in the dist directory covered by the user's src/ngsw-config.json configuration.

如果某个特定的文件未能通过验证,Angular Service Worker 就会尝试用 “cache-busting” URL 为参数重新获取内容,以消除浏览器或中间缓存的影响。 如果该内容也未能通过验证,则 Service Worker 会认为该应用的整个版本都无效,并停止用它提供服务。 如有必要,Service Worker 会进入安全模式,这些请求将退化为直接访问网络。 如果服务无效、损坏或内容过期的风险很高,则会选择不使用缓存。

If a particular file fails validation, the Angular service worker attempts to re-fetch the content using a "cache-busting" URL parameter to eliminate the effects of browser or intermediate caching. If that content also fails validation, the service worker considers the entire version of the app to be invalid and it stops serving the app. If necessary, the service worker enters a safe mode where requests fall back on the network, opting not to use its cache if the risk of serving invalid, broken, or outdated content is high.

导致哈希值不匹配的原因有很多:

Hash mismatches can occur for a variety of reasons:

  • 在源服务器和最终用户之间缓存图层可能会提供陈旧的内容。

    Caching layers in between the origin server and the end user could serve stale content.

  • 非原子化的部署可能会导致 Angular Service Worker 看到部分更新后的内容。

    A non-atomic deployment could result in the Angular service worker having visibility of partially updated content.

  • 构建过程中的错误可能会导致更新了资源,却没有更新 ngsw.json。 反之,也可能发生没有更新资源,却更新了 ngsw.json 的情况。

    Errors during the build process could result in updated resources without ngsw.json being updated. The reverse could also happen resulting in an updated ngsw.json without updated resources.

不带哈希的内容

Unhashed content

ngsw.json 清单中唯一带哈希值的资源就是构建清单时 dist 目录中的资源。 而其他资源,特别是从 CDN 加载的资源,其内容在构建时是未知的,或者会比应用程序部署得更频繁。

The only resources that have hashes in the ngsw.json manifest are resources that were present in the dist directory at the time the manifest was built. Other resources, especially those loaded from CDNs, have content that is unknown at build time or are updated more frequently than the app is deployed.

如果 Angular Service Worker 没有哈希可以验证给定的资源,它仍然会缓存它的内容,但会使用 “重新验证时失效” 的策略来承认HTTP缓存头。 也就是说,当被缓存资源的 HTTP 缓存头指出该资源已过期时,Angular Service Worker 将继续提供内容,并尝试在后台刷新资源。 这样,那些被破坏的非哈希资源留在缓存中的时间就不会超出为它配置的生命周期。

If the Angular service worker does not have a hash to validate a given resource, it still caches its contents but it honors the HTTP caching headers by using a policy of "stale while revalidate." That is, when HTTP caching headers for a cached resource indicate that the resource has expired, the Angular service worker continues to serve the content and it attempts to refresh the resource in the background. This way, broken unhashed resources do not remain in the cache beyond their configured lifetimes.

App 选项卡

App tabs

如果应用程序的资源版本突然发生了变化或没有给出警告,就可能会有问题。有关这些问题的描述,请参阅前面的 版本 部分。

It can be problematic for an app if the version of resources it's receiving changes suddenly or without warning. See the Versions section above for a description of such issues.

Angular Service Worker 会保证:正在运行的应用程序会继续运行和当前应用相同的版本。 而如果在新的 Web 浏览器选项卡中打开了该应用的另一个实例,则会提供该应用的最新版本。 因此,这个新标签可以和原始标签同时运行不同版本的应用。

The Angular service worker provides a guarantee: a running app will continue to run the same version of the app. If another instance of the app is opened in a new web browser tab, then the most current version of the app is served. As a result, that new tab can be running a different version of the app than the original tab.

值得注意的是,这种担保比普通的 Web 部署模型提供的担保还要更强一点。 如果没有 Service Worker,则不能保证稍后在这个正在运行的应用中惰性加载的代码 和其初始代码的版本是一样的。

It's important to note that this guarantee is stronger than that provided by the normal web deployment model. Without a service worker, there is no guarantee that code lazily loaded later in a running app is from the same version as the initial code for the app.

Angular Service Worker 为什么可能会更改运行中的应用的版本有几个有限的原因。 其中一些是因为出错了:

There are a few limited reasons why the Angular service worker might change the version of a running app. Some of them are error conditions:

  • 由于哈希验证失败,当前版本变成了无效的。

    The current version becomes invalid due to a failed hash.

  • 某个无关的错误导致 Service Worker 进入了安全模式,或者说,它被暂时禁用了。

    An unrelated error causes the service worker to enter safe mode; that is, temporary deactivation.

Angular Service Worker 能知道在任何指定的时刻正在使用哪些版本, 并清除那些没有被任何选项卡使用的版本。

The Angular service worker is aware of which versions are in use at any given moment and it cleans up versions when no tab is using them.

另一些可能导致 Angular Service Worker 在运行期间改变版本的因素是一些正常事件:

Other reasons the Angular service worker might change the version of a running app are normal events:

  • 页面被重新加载/刷新。

    The page is reloaded/refreshed.

  • 该页面通过 SwUpdate 服务请求立即激活这个更新。

    The page requests an update be immediately activated via the SwUpdate service.

Service Worker 更新

Service worker updates

Angular Service Worker 是一个运行在Web浏览器中的小脚本。 有时,这个 Service Worker 也可能会需要更新,以修复错误和增强特性。

The Angular service worker is a small script that runs in web browsers. From time to time, the service worker will be updated with bug fixes and feature improvements.

首次打开应用时或在一段非活动时间之后再访问应用程序时,就会下载 Angular Service Worker。 如果 Service Worker 发生了变化,Service Worker 就会在后台进行更新。

The Angular service worker is downloaded when the app is first opened and when the app is accessed after a period of inactivity. If the service worker has changed, the service worker will be updated in the background.

Angular Service Worker 的大部分更新对应用程序来说都是透明的 - 旧缓存仍然有效,其内容仍然能正常使用。 但是,在 Angular Service Worker 中可能偶尔会有错误修复或新功能,需要让旧的缓存失效。 这时,应用程序就从会网络上透明地进行刷新。

Most updates to the Angular service worker are transparent to the app—the old caches are still valid and content is still served normally. However, occasionally a bugfix or feature in the Angular service worker requires the invalidation of old caches. In this case, the app will be refreshed transparently from the network.

调试 Angular Service Worker

Debugging the Angular service worker

偶尔,可能会需要检查运行中的 Angular Service Worker,以调查问题或确保它在按设计运行。 浏览器提供了用于调试 Service Worker 的内置工具,而且 Angular Service Worker 本身也包含了一些有用的调试功能。

Occasionally, it may be necessary to examine the Angular service worker in a running state to investigate issues or to ensure that it is operating as designed. Browsers provide built-in tools for debugging service workers and the Angular service worker itself includes useful debugging features.

定位并分析调试信息

Locating and analyzing debugging information

Angular Service Worker 会在虚拟目录 ngsw/ 下暴露出调试信息。 目前,它暴露的唯一的 URL 是 ngsw/state。 下面是这个调试页面中的一段范例内容:

The Angular service worker exposes debugging information under the ngsw/ virtual directory. Currently, the single exposed URL is ngsw/state. Here is an example of this debug page's contents:

NGSW Debug Info: Driver state: NORMAL ((nominal)) Latest manifest hash: eea7f5f464f90789b621170af5a569d6be077e5c Last update check: never === Version eea7f5f464f90789b621170af5a569d6be077e5c === Clients: 7b79a015-69af-4d3d-9ae6-95ba90c79486, 5bc08295-aaf2-42f3-a4cc-9e4ef9100f65 === Idle Task Queue === Last update tick: 1s496u Last update run: never Task queue: * init post-load (update, cleanup) Debug log:
      
      
  1. NGSW Debug Info:
  2.  
  3. Driver state: NORMAL ((nominal))
  4. Latest manifest hash: eea7f5f464f90789b621170af5a569d6be077e5c
  5. Last update check: never
  6.  
  7. === Version eea7f5f464f90789b621170af5a569d6be077e5c ===
  8.  
  9. Clients: 7b79a015-69af-4d3d-9ae6-95ba90c79486, 5bc08295-aaf2-42f3-a4cc-9e4ef9100f65
  10.  
  11. === Idle Task Queue ===
  12. Last update tick: 1s496u
  13. Last update run: never
  14. Task queue:
  15.  
  16. * init post-load (update, cleanup)
  17.  
  18. Debug log:

驱动程序的状态

Driver state

第一行表示驱动程序的状态:

The first line indicates the driver state:

Driver state: NORMAL ((nominal))
      
      Driver state: NORMAL ((nominal))
    

NORMAL 表示这个 Service Worker 正在正常运行,并且没有处于降级运行的状态。

NORMAL indicates that the service worker is operating normally and is not in a degraded state.

有两种可能的降级状态:

There are two possible degraded states:

  • EXISTING_CLIENTS_ONLY:这个 Service Worker 没有该应用的最新已知版本的干净副本。 较旧的缓存版本可以被安全的使用,所以现有的选项卡将继续使用较旧的版本运行本应用, 但新的应用将从网络上加载。

    EXISTING_CLIENTS_ONLY: the service worker does not have a clean copy of the latest known version of the app. Older cached versions are safe to use, so existing tabs continue to run from cache, but new loads of the app will be served from the network.

  • SAFE_MODE:Service Worker 不能保证使用缓存数据的安全性。 发生了意外错误或所有缓存版本都无效。 这时所有的流量都将从网络提供,尽量少运行 Service Worker 中的代码。

    SAFE_MODE: the service worker cannot guarantee the safety of using cached data. Either an unexpected error occurred or all cached versions are invalid. All traffic will be served from the network, running as little service worker code as possible.

在这两种情况下,后面的括号注解中都会提供导致 Service Worker 进入降级状态的错误信息。

In both cases, the parenthetical annotation provides the error that caused the service worker to enter the degraded state.

最新清单的哈希

Latest manifest hash

Latest manifest hash: eea7f5f464f90789b621170af5a569d6be077e5c
      
      Latest manifest hash: eea7f5f464f90789b621170af5a569d6be077e5c
    

这是 Service Worker 所知道的应用最新版本的 SHA1 哈希值。

This is the SHA1 hash of the most up-to-date version of the app that the service worker knows about.

最后一次更新检查

Last update check

Last update check: never
      
      Last update check: never
    

这表示 Service Worker 最后一次检查应用程序的新版本或更新的时间。“never” 表示 Service Worker 从未检查过更新。

This indicates the last time the service worker checked for a new version, or update, of the app. never indicates that the service worker has never checked for an update.

在这个调试文件范例中,这次更新检查目前是已排期的,如下一节所述。

In this example debug file, the update check is currently scheduled, as explained the next section.

版本

Version

=== Version eea7f5f464f90789b621170af5a569d6be077e5c === Clients: 7b79a015-69af-4d3d-9ae6-95ba90c79486, 5bc08295-aaf2-42f3-a4cc-9e4ef9100f65
      
      === Version eea7f5f464f90789b621170af5a569d6be077e5c ===

Clients: 7b79a015-69af-4d3d-9ae6-95ba90c79486, 5bc08295-aaf2-42f3-a4cc-9e4ef9100f65
    

在这个例子中,Service Worker 拥有一个版本的应用程序缓存并用它服务于两个不同的选项卡。 请注意,这个版本哈希值是上面列出的“最新清单的哈希”。 它的两个客户运行的都是最新版本。每个客户都用浏览器中 Clients API的 ID 列了出来。

In this example, the service worker has one version of the app cached and being used to serve two different tabs. Note that this version hash is the "latest manifest hash" listed above. Both clients are on the latest version. Each client is listed by its ID from the Clients API in the browser.

空闲任务队列

Idle task queue

=== Idle Task Queue === Last update tick: 1s496u Last update run: never Task queue: * init post-load (update, cleanup)
      
      === Idle Task Queue ===
Last update tick: 1s496u
Last update run: never
Task queue:

 * init post-load (update, cleanup)
    

空闲任务队列是 Service Worker 中所有在后台发生的未决任务的队列。 如果这个队列中存在任何任务,则列出它们的描述。 在这个例子中,Service Worker 安排的任务是一个用于更新检查和清除过期缓存的后期初始化操作。

The Idle Task Queue is the queue of all pending tasks that happen in the background in the service worker. If there are any tasks in the queue, they are listed with a description. In this example, the service worker has one such task scheduled, a post-initialization operation involving an update check and cleanup of stale caches.

最后的 tick/run 计数器给出了与特定事件发生有关的空闲队列中的时间。 “Last update run” 计数器显示的是上次执行空闲任务的时间。 “Last update tick” 显示的是自上次事件以来可能要处理的队列的时间。

The last update tick/run counters give the time since specific events happened related to the idle queue. The "Last update run" counter shows the last time idle tasks were actually executed. "Last update tick" shows the time since the last event after which the queue might be processed.

调试日志

Debug log

Debug log:
      
      Debug log:
    

在 Service Worker 中出现的任何错误都会记录在这里。

Errors that occur within the service worker will be logged here.

开发者工具

Developer Tools

Chrome 等浏览器提供了能与 Service Worker 交互的开发者工具。 这些工具在使用得当时非常强大,但也要牢记一些事情。

Browsers such as Chrome provide developer tools for interacting with service workers. Such tools can be powerful when used properly, but there are a few things to keep in mind.

  • 使用开发人员工具时,Service Worker 将继续在后台运行,并且不会重新启动。 这可能会导致开着 Dev Tools 时的行为与用户实际遇到的行为不一样。

    When using developer tools, the service worker is kept running in the background and never restarts. This can cause behavior with Dev Tools open to differ from behavior a user might experience.

  • 如果你查看缓存存储器的查看器,缓存就会经常过期。右键单击缓存存储器的标题并刷新缓存。

    If you look in the Cache Storage viewer, the cache is frequently out of date. Right click the Cache Storage title and refresh the caches.

在 Service Worker 页停止并重新启动这个 Service Worker 将会触发一次更新检查。

Stopping and starting the service worker in the Service Worker pane triggers a check for updates.

Service Worker 的安全性

Service Worker Safety

像任何复杂的系统一样,错误或损坏的配置可能会导致 Angular Service Worker 以不可预知的方式工作。 虽然它在设计时就尝试将此类问题的影响降至最低,但是,如果管理员需要快速停用 Service Worker, Angular Service Worker 也包含多种故障保护机制。

Like any complex system, bugs or broken configurations can cause the Angular service worker to act in unforeseen ways. While its design attempts to minimize the impact of such problems, the Angular service worker contains several failsafe mechanisms in case an administrator ever needs to deactivate the service worker quickly.

故障保护机制

Fail-safe

要停用 Service Worker,请删除或重命名 ngsw-config.json 文件。 当 Service Worker 对 ngsw.json 的请求返回 404 时,Service Worker 就会删除它的所有缓存并注销自己,本质上就是自毁。

To deactivate the service worker, remove or rename the ngsw-config.json file. When the service worker's request for ngsw.json returns a 404, then the service worker removes all of its caches and de-registers itself, essentially self-destructing.

Safety Worker

@angular/service-worker NPM 包中还包含一个小脚本safety-worker.js,当它被加载时就会把它自己从浏览器中注销。 这个脚本可以作为终极武器来摆脱那些已经安装在客户端页面上的不想要的 Service Worker。

Also included in the @angular/service-worker NPM package is a small script safety-worker.js, which when loaded will unregister itself from the browser. This script can be used as a last resort to get rid of unwanted service workers already installed on client pages.

要特别注意的是,你不能直接注册这个 Safety Worker,因为具有已缓存状态的旧客户端可能无法看到一个新的、用来安装 另一个 worker 脚本的 index.html。 相反,你必须在想要注销的 Service Worker 脚本的 URL 中提供 safety-worker.js 的内容, 而且必须持续这样做,直到确定所有用户都已成功注销了原有的 Worker。 对大多数网站而言,这意味着你应该永远为旧的 Service Worker URL 提供 这个 Safety Worker。

It's important to note that you cannot register this worker directly, as old clients with cached state may not see a new index.html which installs the different worker script. Instead, you must serve the contents of safety-worker.js at the URL of the Service Worker script you are trying to unregister, and must continue to do so until you are certain all users have successfully unregistered the old worker. For most sites, this means that you should serve the safety worker at the old Service Worker URL forever.

这个脚本可以用来停用 @angular/service-worker 以及任何其它曾在你的站点上提供过的 Service Worker。

This script can be used both to deactivate @angular/service-worker as well as any other Service Workers which might have been served in the past on your site.

关于 Angular Service Worker 的更多信息

More on Angular service workers

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