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An App Engine application has a configuration file in its root directory named app.yaml
. This file describes which App Engine runtime environment the application uses, the version of the source code, and which handler scripts should process which URLs. app.yaml
is uploaded to App Engine with the application source code.
The following is an example of an app.yaml
file:
application: myapp version: 1 runtime: python api_version: 1 handlers: - url: / script: home.py - url: /index\.html script: home.py - url: /stylesheets static_dir: stylesheets - url: /(.*\.(gif|png|jpg)) static_files: static/\1 upload: static/(.*\.(gif|png|jpg)) - url: /admin/.* script: admin.py login: admin - url: /.* script: not_found.py
The syntax of app.yaml
is the YAML format. For more information about this syntax, see the YAML website for more information.
Tip: The YAML format supports comments. A line that begins with a pound (#
) character is ignored:# This is a comment.
URL and file path patterns use POSIX extended regular expression syntax, excluding collating elements and collation classes. Back-references to grouped matches (e.g. \1
) are supported, as are these Perl extensions: \w \W \s \S \d \D
(This is similar to Codesite search, plus back-reference support.)
An app.yaml
file must include one of each of the following elements:
application
The application identifier. This is the identifier you selected when you created the application in the Administration Console.
application: myapp
version
A version specifier for the application code. App Engine retains a copy of your application for each version
used. An administrator can change which major version of the application is public using the Administration Console, and can test non-public versions before making them public.
Each version of an application retains its own copy of app.yaml
. When an application is uploaded, the version mentioned in the app.yaml
file being uploaded is the version that gets created or replaced by the upload.
On the Administration Console, the version number appears as a major version (version
), and a minor version that corresponds to the number of times this major version has been uploaded. Only the latest major version is retained.
version: 1
runtime
The name of the App Engine runtime environment used by this application. At this time, App Engine has one runtime environment: python
runtime: python
api_version
The version of the API in the given runtime environment used by this application. When Google releases a new version of a runtime environment's API, your application will continue to use the one for which it was written. To upgrade your application to the new API, you change this value and upload the upgraded code.
At this time, App Engine has one version of the python
runtime environment: 1
api_version: 1
handlers
A list of URL patterns and descriptions of how they should be handled. App Engine can handle URLs by executing application code, or by serving static files uploaded with the code, such as images, CSS or JavaScript.
Patterns are evaluated in the order they appear in the app.yaml
, from top to bottom. The first mapping whose pattern matches the URL is the one used to handle the request.
There are two kinds of handlers: script handlers, and static file handlers. A script handler runs a Python script in your application to determine the response for the given URL. A static file handler returns the contents of a file, such as an image, as the response.
See Script Handlers and Handlers for Static Files below for more information on this value.
handlers: - url: /images static_dir: static/images - url: /.* script: myapp.py
A script handler executes a Python script to handle the request that matches the URL pattern. The mapping defines a URL pattern to match, and the script to be executed.
url
The URL pattern, as a regular expression. The expression can contain groupings that can be referred to in the file path to the script with regular expression back-references.
For example, /profile/(.*?)/(.*)
would match the URL /profile/edit/manager
and use edit
and manager
as the first and second groupings.
handlers: - url: /profile/(.*?)/(.*) script: /employee/\2/\1.py
script
The path to the script, from the application root directory.
As in the previous example, with the groupings edit
and manager
, the script path /employee/\2/\1.py
uses the full path /employee/manager/edit.py
.
The following examples map URLs to scripts:
handlers: # The root URL (/) is handled by the index.py script. No other URLs match this pattern. - url: / script: index.py # The URL /index.html is also handled by the index.py script. - url: /index\.html script: index.py # A regular expression can map parts of the URL to the file path of the script. - url: /browse/(books|videos|tools) script: \1/catalog.py # All other URLs use the not_found.py script. - url: /.* script: not_found.py
Static files are files to be served directly to the user for a given URL, such as images, CSS stylesheets, or JavaScript source files. Static file handlers describe which files in the application directory are static files, and which URLs serve them.
For efficiency, App Engine stores and serves static files separately from application files. Static files are not available in the application's file system. If you have data files that need to be read by the application code, the data files must be application files, and must not be matched by a static file pattern.
Unless told otherwise, web browsers retain files they load from a website for a limited period of time. You can define a global default cache period for all static file handlers for an application by including the default_expiration
element, a top-level element. You can also configure a cache duration for specific static file handler. (Script handlers can set cache durations by returning the appropriate HTTP headers to the browser.)
default_expiration
The length of time a static file served by a static file handler ought to be cached in the user's browser, if the handler does not specify its own expiration
. 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 loaded by the browser.
default_expiration
is optional. If omitted, the default behavior is to allow the browser to determine its own cache duration.
For example:
application: myapp version: 1 runtime: python api_version: 1 default_expiration: "4d 5h" handlers: # ...
Static file handlers can be defined in two ways: as a directory structure of static files that maps to a URL path, or as a pattern that maps URLs to specific files.
A static directory handler makes it easy to serve the entire contents of a directory as static files. Each file is served using the MIME type that corresponds with its filename extension unless overridden by the directory's mime_type
setting. All of the files in the given directory are uploaded as static files, and none of them can be run as scripts.
url
A URL prefix. This value uses regular expression syntax (and so regexp special characters must be escaped), but it should not contain groupings. All URLs that begin with this prefix are handled by this handler, using the portion of the URL after the prefix as part of the file path.
static_dir
The path to the directory containing the static files, from the application root directory. Everything after the end of the matched url
pattern is appended to static_dir
to form the full path to the requested file.
All files in this directory are uploaded with the application as static files.
mime_type
Optional. If specified, all files served by this handler will be served using the specified MIME type. If not specified, the MIME type for a file will be derived from the file's filename extension.
For more information about the possible MIME media types, see the IANA MIME Media Types website.
expiration
The length of time a static file served by this handler ought to be cached in the user's browser. 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 loaded by the browser.
expiration
is optional. If omitted, the application's default_expiration
is used.
For example:
handlers: # All URLs beginning with /stylesheets are treated as paths to static files in # the stylesheets/ directory. Note that static_dir handlers do not use a # regular expression for the URL pattern, only a prefix. - url: /stylesheets static_dir: stylesheets
A static file handler associates a URL pattern with paths to static files uploaded with the application. The URL pattern regular expression can define regular expression groupings to be used in the construction of the file path. You can use this instead of static_dir
to map to specific files in a directory structure without mapping the entire directory.
Static files cannot be the same as application code files. If a static file path matches a path to a script used in a dynamic handler, the script will not be available to the dynamic handler.
The following static_dir
and static_files
handlers are equivalent:
- url: /images static_dir: static/images - url: /images/(.*) static_files: static/images/\1 upload: static/images/(.*)
url
The URL pattern, as a regular expression. The expression can contain groupings that can be referred to in the file path to the script with regular expression back-references.
For example, /item-(.*?)/category-(.*)
would match the URL /item-127/category-fruit
, and use 127
and fruit
as the first and second groupings.
handlers: - url: /item-(.*?)/category-(.*) static_files: archives/\2/items/\1
static_files
The path to the static files matched by the URL pattern, from the application root directory. The path can refer to text matched in groupings in the URL pattern.
As in the previous example, archives/\2/items/\1
inserts the second and first groupings matched in place of \2
and \1
, respectively. With the pattern in the example above, the file path would be archives/fruit/items/127
.
upload
A regular expression that matches the file paths for all files that will be referenced by this handler. This is necessary because the handler cannot determine which files in your application directory correspond with the given url
and static_files
patterns. Static files are uploaded and handled separately from application files.
The example above might use the following upload
pattern: archives/(.*?)/items/(.*)
mime_type
Optional. If specified, all files served by this handler will be served using the specified MIME type. If not specified, the MIME type for a file will be derived from the file's filename extension.
For more information about the possible MIME media types, see the IANA MIME Media Types website.
expiration
The length of time a static file served by this handler ought to be cached in the user's browser. 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 loaded by the browser.
expiration
is optional. If omitted, the application's default_expiration
is used.
For example:
handlers: # All URLs ending in .gif .png or .jpg are treated as paths to static files in # the static/ directory. The URL pattern is a regexp, with a grouping that is # inserted into the path to the file. - url: /(.*\.(gif|png|jpg)) static_files: static/\1 upload: static/(.*\.(gif|png|jpg))
Any URL handler can have a login
setting to restrict visitors to only those users who have signed in, or just those users who are administrators for the application. When a URL handler with a login
setting matches a URL, the handler first checks whether the user has signed in to the application with a Google account. If not, the user is redirected to the Google sign-in page, and is redirected back to the application URL after signing in or creating an account.
If the setting is login: required
, once the user has signed in, the handler proceeds normally.
If the setting is login: admin
, once the user has signed in, the handler checks whether the user is an administrator for the application. If not, the user is given an error message. If the user is an administrator, the handler proceeds.
If an application needs different behavior, the application can implement the user handling itself. See the Users API for more information.
An example:
handlers: - url: /profile/.* script: user_profile.py login: required - url: /admin/.* script: admin.py login: admin - url: /.* script: welcome.py
Files in your application directory whose paths match a static_dir
path or a static_files
upload
path are considered to be static files. All other files in the application directory are considered to be application program and data files.
The skip_files
element specifies which files in the application directory are not to be uploaded to App Engine. The value is a regular expression. Any filename that matches the regular expression is omitted from the list of files to upload when the application is uploaded.
skip_files
has the following default value:
skip_files: | ^(.*/)?( (app\.yaml)| (app\.yml)| (index\.yaml)| (index\.yml)| (#.*#)| (.*~)| (.*\.py[co])| (.*/RCS/.*)| (\..*)| )$
The default pattern excludes the configuration files app.yaml
, app.yml
, index.yaml
, index.yml
(configuration is sent to the server separately), Emacs backup files with names of the form #...#
and ...~
, .pyc
and .pyo
files, files in an RCS
revision control directory, and Unix hidden files with names beginning with a dot (.
).
If a new value is specified in app.yaml
, it overrides this value. To extend this pattern, copy and paste it into your configuration with your extensions.
You can refer to the Python library directory in an app.yaml
script path using $PYTHON_LIB
. This is only useful for setting up handlers whose scripts are included in the App Engine libraries.
For example, $PYTHON_LIB/google/appengine/ext/admin
is an administrative application similar to the developer console feature of the development web server that can run as part of your application on App Engine itself. To set it up, include configuration for a script handler using its path:
handlers: - url: /admin/.* script: $PYTHON_LIB/google/appengine/ext/admin login: admin
Several URL paths are reserved by App Engine for features or administrative purposes. Script handler and static file handler paths will never match these paths.
The following URL paths are reserved:
/_ah/
/form