Functions best practices

This document describes best practices for designing, implementing, testing, and deploying Cloud Run functions.

Correctness

This section describes general best practices for designing and implementing Cloud Run functions.

Write idempotent functions

Your functions should produce the same result even if they are called multiple times. This lets you retry an invocation if the previous invocation fails part way through your code. For more information, see retrying event-driven functions.

Ensure HTTP functions send an HTTP response

If your function is HTTP-triggered, remember to send an HTTP response, as shown below. Failing to do so can result in your function executing until timeout. If this occurs, you will be charged for the entire timeout time. Timeouts may also cause unpredictable behavior or cold starts on subsequent invocations, resulting in unpredictable behavior or additional latency.

Node.js 

const functions = require('@google-cloud/functions-framework');
const escapeHtml = require('escape-html');

/**
 * Responds to an HTTP request using data from the request body parsed according
 * to the "content-type" header.
 *
 * @param {Object} req Cloud Function request context.
 * @param {Object} res Cloud Function response context.
 */
functions.http('helloHttp', (req, res) => {
  res.send(`Hello ${escapeHtml(req.query.name || req.body.name || 'World')}!`);
});

Python 


import functions_framework


from markupsafe import escape

@functions_framework.http
def hello_http(request):
    """HTTP Cloud Function.
    Args:
        request (flask.Request): The request object.
        <https://flask.palletsprojects.com/en/1.1.x/api/#incoming-request-data>
    Returns:
        The response text, or any set of values that can be turned into a
        Response object using `make_response`
        <https://flask.palletsprojects.com/en/1.1.x/api/#flask.make_response>.
    """
    request_json = request.get_json(silent=True)
    request_args = request.args

    if request_json and "name" in request_json:
        name = request_json["name"]
    elif request_args and "name" in request_args:
        name = request_args["name"]
    else:
        name = "World"
    return f"Hello {escape(name)}!"

Go 


// Package helloworld provides a set of Cloud Functions samples.
package helloworld

import (
	"encoding/json"
	"fmt"
	"html"
	"net/http"

	"github.com/GoogleCloudPlatform/functions-framework-go/functions"
)

func init() {
	functions.HTTP("HelloHTTP", HelloHTTP)
}

// HelloHTTP is an HTTP Cloud Function with a request parameter.
func HelloHTTP(w http.ResponseWriter, r *http.Request) {
	var d struct {
		Name string `json:"name"`
	}
	if err := json.NewDecoder(r.Body).Decode(&d); err != nil {
		fmt.Fprint(w, "Hello, World!")
		return
	}
	if d.Name == "" {
		fmt.Fprint(w, "Hello, World!")
		return
	}
	fmt.Fprintf(w, "Hello, %s!", html.EscapeString(d.Name))
}

Java 


import com.google.cloud.functions.HttpFunction;
import com.google.cloud.functions.HttpRequest;
import com.google.cloud.functions.HttpResponse;
import com.google.gson.Gson;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.logging.Logger;

public class HelloHttp implements HttpFunction {
  private static final Logger logger = Logger.getLogger(HelloHttp.class.getName());

  private static final Gson gson = new Gson();

  @Override
  public void service(HttpRequest request, HttpResponse response)
      throws IOException {
    // Check URL parameters for "name" field
    // "world" is the default value
    String name = request.getFirstQueryParameter("name").orElse("world");

    // Parse JSON request and check for "name" field
    try {
      JsonElement requestParsed = gson.fromJson(request.getReader(), JsonElement.class);
      JsonObject requestJson = null;

      if (requestParsed != null && requestParsed.isJsonObject()) {
        requestJson = requestParsed.getAsJsonObject();
      }

      if (requestJson != null && requestJson.has("name")) {
        name = requestJson.get("name").getAsString();
      }
    } catch (JsonParseException e) {
      logger.severe("Error parsing JSON: " + e.getMessage());
    }

    var writer = new PrintWriter(response.getWriter());
    writer.printf("Hello %s!", name);
  }
}

C# 

using Google.Cloud.Functions.Framework;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using System.IO;
using System.Text.Json;
using System.Threading.Tasks;

namespace HelloHttp;

public class Function : IHttpFunction
{
    private readonly ILogger _logger;

    public Function(ILogger<Function> logger) =>
        _logger = logger;

    public async Task HandleAsync(HttpContext context)
    {
        HttpRequest request = context.Request;
        // Check URL parameters for "name" field
        // "world" is the default value
        string name = ((string) request.Query["name"]) ?? "world";

        // If there's a body, parse it as JSON and check for "name" field.
        using TextReader reader = new StreamReader(request.Body);
        string text = await reader.ReadToEndAsync();
        if (text.Length > 0)
        {
            try
            {
                JsonElement json = JsonSerializer.Deserialize<JsonElement>(text);
                if (json.TryGetProperty("name", out JsonElement nameElement) &&
                    nameElement.ValueKind == JsonValueKind.String)
                {
                    name = nameElement.GetString();
                }
            }
            catch (JsonException parseException)
            {
                _logger.LogError(parseException, "Error parsing JSON request");
            }
        }

        await context.Response.WriteAsync($"Hello {name}!", context.RequestAborted);
    }
}

Ruby 

require "functions_framework"
require "cgi/escape"
require "json"

FunctionsFramework.http "hello_http" do |request|
  # The request parameter is a Rack::Request object.
  # See https://www.rubydoc.info/gems/rack/Rack/Request
  name = request.params["name"] ||
         begin
           request.body.rewind
           JSON.parse(request.body.read)["name"]
         rescue StandardError
           nil
         end ||
         "World"
  # Return the response body as a string.
  # You can also return a Rack::Response object, a Rack response array, or
  # a hash which will be JSON-encoded into a response.
  "Hello #{CGI.escape_html name}!"
end

PHP 

<?php

use Google\CloudFunctions\FunctionsFramework;
use Psr\Http\Message\ServerRequestInterface;

// Register the function with Functions Framework.
// This enables omitting the `FUNCTIONS_SIGNATURE_TYPE=http` environment
// variable when deploying. The `FUNCTION_TARGET` environment variable should
// match the first parameter.
FunctionsFramework::http('helloHttp', 'helloHttp');

function helloHttp(ServerRequestInterface $request): string
{
    $name = 'World';
    $body = $request->getBody()->getContents();
    if (!empty($body)) {
        $json = json_decode($body, true);
        if (json_last_error() != JSON_ERROR_NONE) {
            throw new RuntimeException(sprintf(
                'Could not parse body: %s',
                json_last_error_msg()
            ));
        }
        $name = $json['name'] ?? $name;
    }
    $queryString = $request->getQueryParams();
    $name = $queryString['name'] ?? $name;

    return sprintf('Hello, %s!', htmlspecialchars($name));
}

Do not start background activities

Background activity is anything that happens after your function has terminated. A function invocation finishes once the function returns or otherwise signals completion, such as by calling the callback argument in Node.js event-driven functions. Any code run after graceful termination cannot access the CPU and will not make any progress.

In addition, when a subsequent invocation is executed in the same environment, your background activity resumes, interfering with the new invocation. This may lead to unexpected behavior and errors that are hard to diagnose. Accessing the network after a function terminates usually leads to connections being reset (ECONNRESET error code).

Background activity can often be detected in logs from individual invocations, by finding anything that is logged after the line saying that the invocation finished. Background activity can sometimes be buried deeper in the code, especially when asynchronous operations such as callbacks or timers are present. Review your code to make sure all asynchronous operations finish before you terminate the function.

Always delete temporary files

Local disk storage in the temporary directory is an in-memory filesystem. Files that you write consume memory available to your function, and sometimes persist between invocations. Failing to explicitly delete these files may eventually lead to an out-of-memory error and a subsequent cold start.

You can see the memory used by an individual function by selecting it in the list of functions in the Google Cloud console and choosing the Memory usage plot.

If you need access to long term storage, consider using Cloud Run volume mounts with Cloud Storage or NFS volumes.

You can reduce memory requirements when processing larger files using pipelining. For example, you can process a file on Cloud Storage by creating a read stream, passing it through a stream-based process, and writing the output stream directly to Cloud Storage.

Functions Framework

To ensure that the same dependencies are installed consistently across environments, we recommend that you include the Functions Framework library in your package manager and pin the dependency to a specific version of Functions Framework.

To do this, include your preferred version in the relevant lock file (for example, package-lock.json for Node.js, or requirements.txt for Python).

If Functions Framework is not explicitly listed as a dependency, it will automatically be added during the build process using the latest available version.

Tools

This section provides guidelines on how to use tools to implement, test, and interact with Cloud Run functions.

Local development

Function deployment takes a bit of time, so it is often faster to test the code of your function locally.

Error reporting

In languages that use exception handling, do not throw uncaught exceptions, because they force cold starts in future invocations.

Do not manually exit

Manually exiting can cause unexpected behavior. Please use the following language-specific idioms instead:

Node.js

Do not use process.exit(). HTTP functions should send a response with res.status(200).send(message), and event-driven functions will exit once they return (either implicitly or explicitly).

Python

Do not use sys.exit(). HTTP functions should explicitly return a response as a string, and event-driven functions will exit once they return a value (either implicitly or explicitly).

Go

Do not use os.Exit(). HTTP functions should explicitly return a response as a string, and event-driven functions will exit once they return a value (either implicitly or explicitly).

Java

Do not use System.exit(). HTTP functions should send a response with response.getWriter().write(message), and event-driven functions will exit once they return (either implicitly or explicitly).

C#

Do not use System.Environment.Exit(). HTTP functions should send a response with context.Response.WriteAsync(message), and event-driven functions will exit once they return (either implicitly or explicitly).