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An App Engine app is configured using anapp.yamlfile, that contains the runtime, handlers, scaling, and other general settings
including environment variables.
Aboutapp.yamlfiles
You can specify the runtime configuration for your Ruby app,
including versions and URLs, in theapp.yamlfile. This file acts as a deployment descriptor of a specificserviceversion.
You must first create theapp.yamlfile for thedefaultservice of your app
before you can create and deployapp.yamlfiles for additional services.
Generally, yourapp.yamlfile requires only theruntimeelement for a simple
Ruby app in the standard environment, for
example:
runtime:ruby34
App Engine provides default values for all other settings, including
theF1 instance class, which
determines the memory and CPU resources that are available to your app, andautomatic scaling,
which controls how and when new instances of your app are created.
If you need to override the default settings, create anapp.yamlfile and
specify the settings you need. For more information, seeapp.yamlfile reference.
You can specify a unique name for yourapp.yamlfiles, but then you must
specify the file name with thedeployment
commandas well. For example, if you name yourapp.yamlfileservice-name-app.yamlorapp.standard.yaml, then you must deploy your app using either:
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-09-04 UTC."],[[["\u003cp\u003eThe \u003ccode\u003eapp.yaml\u003c/code\u003e file is essential for configuring an App Engine app, defining runtime, handlers, scaling, and other settings, including environment variables.\u003c/p\u003e\n"],["\u003cp\u003eA \u003ccode\u003edefault\u003c/code\u003e service's \u003ccode\u003eapp.yaml\u003c/code\u003e file must be created before creating and deploying \u003ccode\u003eapp.yaml\u003c/code\u003e files for additional services.\u003c/p\u003e\n"],["\u003cp\u003eA basic Ruby app in the standard environment typically only requires the \u003ccode\u003eruntime\u003c/code\u003e element in its \u003ccode\u003eapp.yaml\u003c/code\u003e file, as App Engine provides defaults for other settings like instance class and scaling.\u003c/p\u003e\n"],["\u003cp\u003eYou can customize your \u003ccode\u003eapp.yaml\u003c/code\u003e filename, but you must then use the specific filename when deploying the app with the \u003ccode\u003egcloud app deploy\u003c/code\u003e command.\u003c/p\u003e\n"],["\u003cp\u003eThe \u003ccode\u003eapp.yaml\u003c/code\u003e file reference has a complete list of all supported elements.\u003c/p\u003e\n"]]],[],null,["# Defining runtime settings\n\n\u003cbr /\u003e\n\n\u003cbr /\u003e\n\n\nAn App Engine app is configured using an `app.yaml`\nfile, that contains the runtime, handlers, scaling, and other general settings\nincluding environment variables.\n\n\nAbout `app.yaml` files\n----------------------\n\n\u003cbr /\u003e\n\nYou can specify the runtime configuration for your Ruby app, including versions and URLs, in the `app.yaml` file. This file acts as a deployment descriptor of a specific [service](/appengine/docs/standard/an-overview-of-app-engine) version.\n\n\u003cbr /\u003e\n\n\nYou must first create the `app.yaml` file for the `default` service of your app\nbefore you can create and deploy `app.yaml` files for additional services.\n\n\nGenerally, your `app.yaml` file requires only the `runtime` element for a simple\nRuby app in the standard environment, for\nexample:\n\n\n runtime: ruby34\n\n\nApp Engine provides default values for all other settings, including\nthe [F1 instance class](/appengine/docs/standard#instance_classes), which\ndetermines the memory and CPU resources that are available to your app, and\n[automatic scaling](/appengine/docs/standard/how-instances-are-managed#scaling_types),\nwhich controls how and when new instances of your app are created.\n\nIf you need to override the default settings, create an `app.yaml` file and\nspecify the settings you need. For more information, see\n[`app.yaml` file reference](/appengine/docs/standard/reference/app-yaml).\n\n\nYou can specify a unique name for your `app.yaml` files, but then you must\nspecify the file name with the [deployment\ncommand](/appengine/docs/standard/testing-and-deploying-your-app)\nas well. For example, if you name your `app.yaml` file `service-name-app.yaml`\nor `app.standard.yaml`, then you must deploy your app using either: \n\n gcloud app deploy service-name-app.yaml\n gcloud app deploy app.standard.yaml\n\nTo learn more about structuring multiple services and `app.yaml` files in your app, see [Structuring web services](/appengine/docs/standard/configuration-files).\n\n\u003cbr /\u003e\n\nAll configuration elements\n--------------------------\n\nFor a complete list of all the supported elements in this configuration file,\nsee the\n[`app.yaml` reference](/appengine/docs/standard/reference/app-yaml)."]]
