appengine-web.xml reference

Region ID

The REGION_ID is an abbreviated code that Google assigns based on the region you select when you create your app. The code does not correspond to a country or province, even though some region IDs may appear similar to commonly used country and province codes. For apps created after February 2020, REGION_ID.r is included in App Engine URLs. For existing apps created before this date, the region ID is optional in the URL.

Learn more about region IDs.

You should use the appengine-web.xml file for configuring your app only if you are migrating an existing app from the App Engine Java 8 runtime to the latest supported Java version and you want to use the legacy bundled services. If you are using an appengine-web.xml in your project, the app.yaml is automatically generated for you at deployment.

App Engine Java applications use a configuration file, named appengine-web.xml, to specify information about your app and to identify which files in the app's WAR file are static files (like images) and which are resource files used by the application.

Syntax

An App Engine Java app must have a file named appengine-web.xml in its WAR, in the directory WEB-INF/. This is an XML file whose root element is .

You can find the Document Type Definition and schema specifications for the appengine-web.xml in the SDK's docs/ directory.

Element Description

Not required if you deploy your app using Google Cloud SDK-based tooling, such as the gcloud app deploy command, IntelliJ or Eclipse plugins, Maven or Gradle plugins. The Google Cloud SDK-based tooling ignore this element and get the project ID from the gcloud config project property. Note that although you can override the project ID using the gcloud command line tool, this sets a machine-wide project ID, which may cause confusion if you are developing multiple projects. The element contains the application's project ID. This is the project ID you register when you create your project in the Google Cloud console.

Optional. If you want to use the App Engine legacy bundled services for second-generation runtimes, set this field to true.

Optional and only for second-generation runtimes. Overrides the default entrypoint which is the process command line that boots the Java application. By default, the generated entrypoint for a F4 instance class (memory settings are calculated from the instance class) is equivalent to the following configuration: 

   xmlns="http://appengine.google.com/ns/1.0">
  
   java
   -showversion -Xms32M -Xmx819M -XX:+UseG1GC -XX:+ParallelRefProcEnabled
   -XX:+PrintCommandLineFlags
   --add-opens java.base/java.lang=ALL-UNNAMED
   --add-opens java.base/java.nio.charset=ALL-UNNAMED
   --add-opens java.logging/java.util.logging=ALL-UNNAMED
   --add-opens java.base/java.util.concurrent=ALL-UNNAMED
   -Dclasspath.runtimebase=/base/java_runtime
   -Djava.class.path=/base/java_runtime/runtime-main.jar
   -Djava.library.path=/base/java_runtime:
   com/google/apphosting/runtime/JavaRuntimeMainWithDefaults
   --fixed_application_path=/workspace
   /base/java_runtime

You can modify the configuration to add extra JVM process flags or define your own process to boot. Notice that the application is deployed in the /workspace directory, while the runtime JARs are located under /base/java_runtime directory.

Learn how to customize the entry point for the Java runtime using environment variables..

Optional. It's possible to reduce request latency by configuring your application to asynchronously write HTTP session data to the datastore: 

 enabled="true" />

With async session persistence turned on, App Engine will submit a Task Queue task to write session data to the datastore before writing the data to memcache. By default the task will be submitted to the `default` queue. If you'd like to use a different queue, add the `queue-name` attribute: 

   enabled="true" queue-name="myqueue"/>

Session data is always written synchronously to memcache. If a request tries to read the session data when memcache is not available (or the session data has been flushed), it will fail over to Datastore, which might not yet have the most recent session data. This means that asynchronous session persistence can cause your application to see stale session data. However, for most applications the latency benefit far outweighs the risk.

Optional. If you are setting entity identifiers automatically, you can change the method employed by setting the auto ID policy. The following are valid options:
default
Default. Uses scattered auto IDs that are large well-distributed integers that are small enough to be represented by 64-bit floats.
legacy
The legacy option will be deprecated in a future release and will eventually be removed. For more information, see the blog post announcing this change.

Optional. For a full explanation, see the automatic scaling section.

Optional. For a full explanation, see the basic scaling section.

Optional. The appengine-web.xml file can define environment variables that are set when the application is running. 


 name="DEFAULT_ENCODING" value="UTF-8" />

To avoid conflicts with your local environment, the development server does not set environment variables based on this file, and requires that the local environment have these variables already set to matching values. 

export DEFAULT_ENCODING="UTF-8"
dev_appserver war

When deployed to App Engine, the environment is created with these variables already set.

Optional. Before an application can receive email, the application must be configured to enable the service. You enable the service for a Java app by including an section in the appengine-web.xml file.

The following inbound service is available:

mail
Allows your application to receive mail.

Optional. The instance class size for this module.

The following instance classes are available when specifying different scaling options:

automatic_scaling
When using automatic scaling, the F1, F2, F4, and F4_1G instance classes are available.
Default: F1 is assigned if you do not specify an instance class along with the automatic_scaling element.
basic_scaling
When using basic scaling, the B1, B2, B4, B4_1G, and B8 instance classes are available.
Default: B2 is assigned if you do not specify a instance class along with the basic_scaling element.
manual_scaling
When using manual scaling, the B1, B2, B4, B4_1G, and B8 instance classes are available.
Default: B2 is assigned if you do not specify a instance class along with the manual_scaling element.

Note: If instance-class is set to F2 or higher, you can optimize your instances by setting max-concurrent-requests to a value higher than 10, which is the default. To find the optimal value, gradually increase it and monitor the performance of your application.

Optional. For a full explanation, see the manual scaling section.

Optional. App Engine uses a "precompilation" process with the Java bytecode of an app to enhance the performance of the app in the Java runtime environment. Precompiled code functions identically to the original bytecode.

If for some reason you prefer that your app not use precompilation, you can turn it off by adding the following to your appengine-web.xml file: 

false

Note: Modules are now named Services and services are still declared in appengine-web.xml files as modules, for example: service_name.

Required if creating a service. Optional for the default service. Each service and each version must have a name. A name can contain numbers, letters, and hyphens. It cannot be longer than 63 characters, start or end with a hyphen, and contain the string `-dot`. Choose a unique name for each service and each version. Don't reuse names between services and versions.

Also see service.

Optional. The is a directory in your application that contains the static files for your application. When a request for a static file is made, the for your application is prepended to the request path. This gives the path of an application file containing the content that is being requested.

The default is /.

For example, the following would map the URL path /index.html to the application file path /static/index.html: 

/static

Optional. The files listed in the element are accessible by the application code using the filesystem. These files are stored on the application servers with the app as opposed to how static files are stored and served.

The element can contain the following elements:

An element designates the files as resource files and available to your application code. These files are only available to your code on a read-only basis and not for traffic serving. Including and excluding files.

Files and directories matching patterns will not be uploaded or available to your application code. However, these files and directories will still be accessible to your application when running on the local Development Server. For more information, see Including and excluding files.

Example: 

   path="/**.xml" />
   path="/feeds/**.xml" />

This example demonstrates how to designate all .xml files as resource files except those in the feeds/ directory and all of its subdirectories.

App Engine resource files are read using java.io.File or javax.servlet.ServletContext.getResource/getResourceAsStream. They are not accessible via Class.getResourceAsStream().

To use the latest supported Java version, you must specify this entry with the value java21.

Example: 
java21

Services were formerly known as modules.

Currently, defining a service as: service_name is supported only by gcloud app commands.

Optional. The element lets you specify a user-managed service account as the identity for the version. The specified service account will be used when accessing other Google Cloud services and executing tasks.

Example: 
[SERVICE_ACCOUNT_NAME]@[PROJECT_ID].iam.gserviceaccount.com

Optional. App Engine includes an implementation of sessions, using the servlet session interface. The implementation stores session data in Datastore for persistence, and also uses memcache for speed. As with most other servlet containers, the session attributes that are set with `session.setAttribute()` during the request are persisted at the end of the request.

This feature is off by default. To turn it on, add the following to appengine-web.xml:

Example: 
true

The implementation creates Datastore entities of the kind _ah_SESSION, and memcache entries using keys with a prefix of _ahs. You can delete these entities using the Dataflow template.

Note: Because App Engine stores session data in Datastore and memcache, all values stored in the session must implement the java.io.Serializable interface.

See async-session-persistence element for reducing the latency of the storage of session data.

Optional. By default, any user can access any URL using either HTTP or HTTPS. You can configure an app to require HTTPS for certain URLs in the deployment descriptor. See Deployment Descriptor: Secure URLs.

If you want to disallow the use of HTTPS for the application, put the following in the appengine-web.xml file: 

false

There is no way to disallow HTTPS for some URL paths and not others in the Java runtime environment.

Optional. When certain errors occur, App Engine serves a generic error page. You can configure your app to serve a custom static file instead of these generic error pages, so long as the custom error data is less than 10 kilobytes. You can set up different static files to be served for each supported error code by specifying the files in your app's appengine-web.xml file. To serve custom error pages, add a section to your appengine-web.xml, as ins this example: 


   file="default_error.html" />
   file="over_quota.html" error-code="over_quota" />

Warning: Make sure that the path to the error response file does not overlap with static file handler paths.

Each file entry indicates a static file that should be served in place of the generic error response. The error-code indicates which error code should cause the associated file to be served. Supported error codes are as follows:

over_quota
Indicates that the app has exceeded a resource quota.
timeout
Served if a deadline is reached before there is a response from your app.

The error-code is optional; if it's not specified, the given file is the default error response for your app.

You can optionally specify a mime-type to use when serving the custom error. See a complete list of MIME types.

Optional. The element specifies patterns that match file paths to include and exclude from the list of static files, overriding or amending the default behavior. Static file are served from dedicated servers and caches that are separate from the application servers and are useful for serving static content such as images, CSS stylesheets or JavaScript files.

The element can contain the following elements:

An element overrides the default behavior of including all non-JSP files. The element can specify HTTP headers to use when responding to request for the specified resources. For more information, see Including and excluding files.

You can override the default static cache expiration by specifying the expiration attribute on the include element. The value is a string of numbers and units, separated by spaces, where units can be d for days, h for hours, m for minutes, and s for seconds. For example, "4d 5h" sets cache expiration to 4 days and 5 hours after the file is first requested. For more information, see Cache expiration.

Files and directories matching patterns will not be uploaded when you deploy your app to App Engine. However, these files and directories will still be accessible to your application when running on the local Development Server. For more information, see Including and excluding files.
Example 

   path="/my_static-files" >
     name="Access-Control-Allow-Origin"
                 value="http://example.org" />

Optional. The appengine-web.xml file can define system properties and environment variables that are set when the application is running. 


   name="myapp.maximum-message-length" value="140" />
   name="myapp.notify-every-n-signups" value="1000" />
   name="myapp.notify-url"
            value="http://www.example.com/signupnotify" />



   name="DEFAULT_ENCODING" value="UTF-8" />

Optional. You can configure an HTTP connector for improving CPU and memory utilization. 

  
     name="appengine.use.httpconnector" value="true"/>

Optional. You can configure the underlying runtime to work on EE8 or EE10 using the following system property. For more information regarding EE support, see Upgrade to Java 21. 

  
     name="appengine.use.EE10" value="true"/>

Starting in Java 21, you can configure your Java web server to use virtual threads. For example: 

  
     name="appengine.use.virtualthreads" value="true"/>
For more information regarding thread support, see Jetty 12 – Virtual Threads Support.

Optional. Possible values, native or urlfetch.

The default value is native, which means that standard Java network classes use the standard Java HTTP(S) transport. To use this setting, you must enable billing for your app, or you will get exceptions, which are documented in Issue requests.

If you set url-stream-handler to urlfetch, URL.openConnection and related methods will use URL Fetch for http and https transport.

urlfetch

The element contains the version identifier for the latest version of the app's code. The version identifier can contain lowercase letters, digits, and hyphens. It cannot begin with the prefix "ah-" and the names "default" and "latest" are reserved and cannot be used.

Version names should begin with a letter, to distinguish them from numeric instances which are always specified by a number. This avoids the ambiguity with URLs like 123.my-module.uc.r.appspot.com, which can be interpreted two ways: If version "123" exists, the target will be version "123" of the given module. If that version does not exist, the target will be instance number 123 of the default version of the module.

Optional. Default: true. Warmup requests are enabled by default for Java applications.

With warmup requests enabled, the App Engine infrastructure issues `GET` requests to /_ah/warmup, initializing servlets, ServletContextListeners, and custom warmup servlets, which allow you to initialize your application's code as it requires. You might need to implement your own handler for /_ah/warmup depending on which of these methods you choose.

To disable warmup requests, specify false for this element: 

false

Optional. Configures your application to use a Serverless VPC Access connector, enabling the application to send requests to internal resources in your VPC network. Specify the fully-qualified name of a connector in the element: 


  projects/[PROJECT_ID]/locations/[REGION]/connectors/[CONNECTOR_NAME]

For more information, see Connecting to internal resources in a VPC network.

Scaling elements

The following table lists the options for defining how you can specify that your application should scale.

For a comparison of the performance features of the scaling types, see Scaling dynamic instances.

Element Description

Optional. Automatic scaling is assumed by default with a default instance class of F1 unless specified otherwise.

The automatic_scaling element sets minimum and maximum levels for number of instances, latency, and concurrent connections for a module.

This element can contain the following elements:

Optional. Specify a value from 0.5 to 0.95.

This parameter specifies the CPU usage threshold at which new instances will be started to handle traffic, enabling you to balance between performance and cost, with lower values increasing performance and increasing cost, and higher values decreasing performance but also decreasing cost. For example, a value of 0.7 means that new instances will be started after CPU usage reaches 70 percent.

Optional. Specify a value from 0.5 to 0.95.

Used with max-concurrent-requests to specify when a new instance is started due to concurrent requests. When the number of concurrent requests reaches a value equal to max-concurrent-requests times target-throughput-utilization, the scheduler starts a new instance.

Optional. The maximum number of instances for App Engine to create for this application version. This is useful to limit the costs of a module. Specify a value between 0 and 2147483647.
Optional. The minimum number of instances for App Engine to create for this module version. These instances serve traffic when requests arrive, and continue to serve traffic even when additional instances are started up as required to handle traffic.

Specify a value from 0 to 1000. You can set the parameter to the value 0 to allow scaling to 0 instances to lower costs when no requests are being served. Note that you are charged for the number of instances specified whether they are receiving traffic or not.

Optional. The number of concurrent requests an automatic scaling instance can accept before the scheduler spawns a new instance (Default: 10, Maximum: 80).

You might experience increased API latency if this setting is too high. Note that the scheduler might spawn a new instance before the actual maximum number of requests is reached.

Note: If instance-class is set to F2 or higher, you can optimize your instances by setting max-concurrent-requests to a value higher than 10, which is the default. To find the optimal value, gradually increase it and monitor the performance of your application.

The maximum number of idle instances that App Engine should maintain for this version. The default value is "automatic." Keep the following in mind:

  • A high maximum reduces the number of idle instances more gradually when load levels return to normal after a spike. This helps your application maintain steady performance through fluctuations in request load, but also raises the number of idle instances (and consequent running costs) during such periods of heavy load.
  • A low maximum keeps running costs lower, but can degrade performance in the face of volatile load levels.

Note: When settling back to normal levels after a load spike, the number of idle instances can temporarily exceed your specified maximum. However, you will not be charged for more instances than the maximum number you've specified.

The maximum amount of time that App Engine should allow a request to wait in the pending queue before starting additional instances to handle requests so that pending latency is reduced.

  • A low maximum means App Engine will start new instances sooner for pending requests, improving performance but raising running costs.
  • A high maximum means users might wait longer for their requests to be served, if there are pending requests and no idle instances to serve them, but your application will cost less to run.

The number of instances to be kept running and ready to serve traffic.This setting only applies to the version that receives most of the traffic. Keep the following in mind:

  • A low minimum helps keep your running costs down during idle periods, but means that fewer instances might be immediately available to respond to a sudden load spike.

  • A high minimum allows you to prime the application for rapid spikes in request load. App Engine keeps the minimum number of instances running to serve incoming requests. You are charged for instances, whether or not they are handling requests. For this feature to function properly, you must make sure that warmup requests are enabled and that your application handles warmup requests.

    If you set a minimum number of idle instances, pending latency will have less effect on your application's performance. Because App Engine keeps idle instances in reserve, it is unlikely that requests will enter the pending queue except in exceptionally high load spikes. You will need to test your application and expected traffic volume to determine the ideal number of instances to keep in reserve.

The minimum amount of time in seconds that App Engine should allow a request to wait in the pending queue before starting a new instance to handle it. Specify a value from 0.01 to 15.

  • A low minimum means requests must spend less time in the pending queue when all existing instances are active. This improves performance but increases the cost of running your application.
  • A high minimum means requests will remain pending longer if all existing instances are active. This lowers running costs but increases the time users must wait for their requests to be served.
Example 
 xmlns="http://appengine.google.com/ns/1.0">
  simple-app
  default
  uno
  F2
  
    0.65
    5
    100
    50

Optional. The element sets the number of instances for a module.

This element can contain the following elements:

Optional. The instance will be shut down this amount of time after receiving its last request. The default is 5 minutes.
Required. The maximum number of instances for App Engine to create for this module version. This is useful to limit the costs of a module.
Example 
 xmlns="http://appengine.google.com/ns/1.0">
  simple-app
  default
  uno
  B8
  
    11
    10m

Optional. The element enables manual scaling for a module and sets the number of instances for a module.

This element can contain the following elements:

The number of instances to assign to the module at the start.
Example 
 xmlns="http://appengine.google.com/ns/1.0">
  simple-app
  default
  uno
  B8
  
    5

Staging elements

Much of the work done during a deployment occurs locally in a preparation step called staging, where JAR files are assembled, JSPs are compiled, and so forth. You can optionally configure certain parts of the staging behavior using staging elements in the application configuration file. Most applications will deploy successfully without manually configuring staging behavior. If your app doesn't deploy, you may need to configure staging using the options shown below.

Element Description

Optional. Most applications do not need to change default behavior.

The staging element allows you to specify a particular staging configuration if needed for deployment.

This element can contain the following elements:

Optional. Split large jar files (> 10 Megabytes) into smaller fragments. (Default: true).

Specifies a comma-separated list of file suffixes. If enable-jar-splitting is enabled, all files that match the suffixes will be excluded from all JARs.

Do not jar classes generated from JSPs. (Default: false).

Jar the contents of WEB-INF/classes. (Default: true).

Delete the JSP source files after compilation. (Default: true).

Input encoding of source files for compilation. (Default: utf-8).

For example:

        
          false

Staging option defaults

The defaults for staging options are different depending on whether you use Google Cloud SDK-based tooling, such as the gcloud CLI, or the Google Cloud SDK-based Maven, Gradle, Eclipse, or IntelliJ plugins.

Staging element App Engine SDK-based defaults - Google Cloud SDK-based defaults
enable-jar-splitting false true
jar-splitting-excludes NA NA
disable-jar-jsps false false
enable-jar-classes false true. This can impact class loading order, so if your app depends on a certain order using the former false default, you can set this to false.
delete-jsps false true
compile-encoding utf-8 utf-8

Include and exclude syntax

Path patterns are specified using zero or more and elements. In a pattern, '*' represents zero or more of any character in a file or directory name, and ** represents zero or more directories in a path. Files and directories matching patterns will not be uploaded when you deploy your app to App Engine. However, these files and directories will still be accessible to your application when running on the local Development Server.

An element overrides the default behavior of including all files. An element applies after all patterns (as well as the default if no explicit is provided).

The following example demonstrates how to designate all .png files as static files (except those in the data/ directory and all of its subdirectories):

<static-files>
  <include path="/**.png" />
  <exclude path="/data/**.png" />
</static-files>

You can also set HTTP headers to use when responding to requests to these static resources.

<static-files>
  <include path="/my_static-files" >
    <http-header name="Access-Control-Allow-Origin"
                 value="http://example.org" />
  </include>
</static-files>

MIME types for static files

By default, static files are served using a MIME type selected based on the filename extension. You can associate custom MIME types with filename extensions for static files using mime-mapping elements in web.xml.

URLFetch timeout

You can set a deadline for each URLFetch request. By default, the deadline for a fetch is 5 seconds. You can change this default by including the following setting in your appengine-web.xml configuration file. Specify the timeout in seconds:

<system-properties>
    <property name="appengine.api.urlfetch.defaultDeadline" value="10"/>
</system-properties>