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If you'd like to use an alternative implementation of Python,
Java, Node.js, Go,
Ruby, PHP, .NET or you write
code in any other language, then custom runtimes are for you. Custom runtimes
allow you to define new runtime environments, which might include additional
components like language interpreters or application servers.
To create a custom runtime, you create a Dockerfile with a base image of your
choice, and then add the docker commands that build your desired runtime
environment. It's important to remember that you are responsible for ensuring
that the components that you specified in your Dockerfile are compatible and
configured to deliver the desired performance.
When you use a custom runtime, you must write your application code to handle
certain flexible environment life-cycle and health checking requests. Start by
reading about how to build a custom
runtime before you begin
developing your application.
Applications that use custom runtimes take advantage of all the various
Google Cloud services by using the public REST APIs or client libraries,
such as the App Engine Admin API and the Google Client
Libraries.
Use the following table to understand how a custom runtime compares to the
existing set of App Engine runtimes:
[[["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 2025-08-25 UTC."],[[["\u003cp\u003eCustom runtimes enable the use of any language or software capable of handling HTTP requests, beyond the standard supported options like Python, Java, and Node.js.\u003c/p\u003e\n"],["\u003cp\u003eDevelopers create custom runtimes by crafting a Dockerfile to define the runtime environment, including any necessary components.\u003c/p\u003e\n"],["\u003cp\u003eUsers of custom runtimes are responsible for the compatibility and performance of the components specified in their Dockerfile.\u003c/p\u003e\n"],["\u003cp\u003eApplications leveraging custom runtimes can access all Google Cloud services via public REST APIs or client libraries.\u003c/p\u003e\n"],["\u003cp\u003eUnlike standard flexible runtimes where the Dockerfile is automatically supplied, developers must hand-write the Dockerfile for custom runtime environments.\u003c/p\u003e\n"]]],[],null,["# About Custom runtimes\n\n\u003cbr /\u003e\n\n\u003cbr /\u003e\n\n\u003cbr /\u003e\n\n\u003cbr /\u003e\n\n\u003cbr /\u003e\n\n\u003cbr /\u003e\n\nIf you'd like to use an alternative implementation of Python,\nJava, Node.js, Go,\nRuby, PHP, .NET or you write\ncode in any other language, then custom runtimes are for you. Custom runtimes\nallow you to define new runtime environments, which might include additional\ncomponents like language interpreters or application servers.\n\nTo create a custom runtime, you create a Dockerfile with a base image of your\nchoice, and then add the `docker` commands that build your desired runtime\nenvironment. It's important to remember that you are responsible for ensuring\nthat the components that you specified in your Dockerfile are compatible and\nconfigured to deliver the desired performance.\n\nWhen you use a custom runtime, you must write your application code to handle\ncertain flexible environment life-cycle and health checking requests. Start by\nreading about how to [build a custom\nruntime](/appengine/docs/flexible/custom-runtimes/build) before you begin\ndeveloping your application.\n\nApplications that use custom runtimes take advantage of all the various\nGoogle Cloud services by using the public REST APIs or client libraries,\nsuch as the [App Engine Admin API](/appengine/docs/admin-api) and the [Google Client\nLibraries](/python/docs/reference).\n\nUse the following table to understand how a custom runtime compares to the\nexisting set of App Engine runtimes:\n\n\u003cbr /\u003e\n\n\u003cbr /\u003e"]]
