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How-to Guide: Running your function as Docker container

This guide shows you how to create a container image for an example function, and how to run said image in a local container on your workstation.

WARNING: The development version of this document may not work with the released version of the functions framework. Please use this document as it appears in the corresponding release if you are using a released version of the library. In particular, buildpacks use the latest release.

Pre-requisites

Verify the docker tool is functional on your workstation:

docker run hello-world
# Output: Hello from Docker! and then some more informational messages.

If needed, use the online instructions to download and install this tool. This guide assumes that you have configured sudoless docker. If you prefer replace all docker commands below with sudo docker.

Verify the pack tool is functional on our workstation. These instructions were tested with v0.17.0, although they should work with newer versions. Some commands may not work with older versions.

pack version
# Output: a version number, e.g., 0.17.0+git-d9cb4e7.build-2045

In this guide we will be using this function:

#include <google/cloud/functions/function.h>
#include <nlohmann/json.hpp>

namespace gcf = ::google::cloud::functions;

gcf::HttpResponse hello_world_http_impl(gcf::HttpRequest request) {
  auto greeting = [r = std::move(request)] {
    auto request_json = nlohmann::json::parse(r.payload(), /*cb=*/nullptr,
                                              /*allow_exceptions=*/false);
    if (request_json.count("name") && request_json["name"].is_string()) {
      return "Hello " + request_json.value("name", "World") + "!";
    }
    return std::string("Hello World!");
  };

  return gcf::HttpResponse{}
      .set_header("content-type", "text/plain")
      .set_payload(greeting());
}

gcf::Function hello_world_http() {
  return gcf::MakeFunction(hello_world_http_impl);
}

Getting the code for this example

This example is included in the Functions Framework for C++ source code repository. Download this code as usual:

cd $HOME
git clone https://github.com/GoogleCloudPlatform/functions-framework-cpp

The rest of this guide will assume you are issuing commands in the framework's clone:

cd $HOME/functions-framework-cpp

Building a Docker image

⚠️ This will automatically download and compile the functions framework and all its dependencies. Consequently, the first build of a function may take several minutes (and up to an hour) depending on the performance of your workstation. Subsequent builds cache many binary artifacts, but these caches are not shared across functions, so plan accordingly.

We use the Google Cloud buildpack builder to create the Docker image containing your function:

pack build \
    --builder gcr.io/buildpacks/builder:v1 \
    --env GOOGLE_FUNCTION_TARGET=hello_world_http \
    --path examples/site/hello_world_http \
    gcf-cpp-hello-world-http

Starting a local container

Start a Docker container in the background the image you just created:

ID=$(docker run --detach --rm -p 8080:8080 gcf-cpp-hello-world-http)

Send a request to your function

You can use curl (or a similar HTTP client) to send requests to your function:

curl http://localhost:8080
# Output: Hello, World!

Cleanup

Stop the background container:

docker kill "${ID}"

And delete the local image:

docker image rm gcf-cpp-hello-world-http