Add "inproc" mode for Golang functions

[alexellis]

Description

Add "inproc" mode for Golang functions

Motivation and Context

Reduce total RAM usage by running a single process for the watchdog and the handler of a function (only possible with Go)

Roundtrip latency may also be improved for function invocations.

How Has This Been Tested?

Initial testing in Kubernetes with a modified template appears to work as expected.

To achieve a similar effect to prefixing each logged line with a Call ID bespoke code will be required:

package function

import (
	"fmt"
	"io"
	"log/slog"
	"os"

	"net/http"
	"time"
)

func Handle(w http.ResponseWriter, r *http.Request) {
	var input []byte

	log := slog.New(slog.NewTextHandler(os.Stdout, opts))
	log = log.With("X-Call-Id", r.Header.Get("X-Call-Id"))

	log.Info("received request")

	if r.Body != nil {
		defer r.Body.Close()

		body, _ := io.ReadAll(r.Body)

		input = body
	}

	log.Info("Sleeping for 1 milliseconds")

	time.Sleep(time.Millisecond * 1)

	log.Info("Sleep done")

	w.WriteHeader(http.StatusOK)
	w.Write([]byte(fmt.Sprintf("Body: %s", string(input))))
}

Initial RAM usage showed as 2Mi and rose over time to 4Mi

$ kubectl top pod -n openfaas-fn| grep "ofw"
ofw-d67d7c474-rpx8c             1m           4Mi  

The printer function from the store is showing about 11Mi of usage and does very little in and of itself other than logging the incoming HTTP request:

$ kubectl top pod -n openfaas-fn| grep "printer"
printer-5c9b5fbf98-gbwn7        1m           11Mi  

Custom template that imports the new watchdog "SDK":

https://github.com/openfaas/golang-http-template/blob/inproc/template/golang-middleware-inproc/main.go

Types of changes

On the plus side - RAM looks to be much smaller as low as 2mb total usage vs the two processes.

On the downside, it's not possible or practical to do stderr/stdout prefixing due to no process boundary between the watchdog and the handler process.

A new template and Dockerfile will be required to support the changes. Builds may be marginally slower since they have to import the watchdog as an "SDK".

Every push will be a single layer binary so this will also take longer vs a tiny Go binary plus the watchdog.

Checklist:

The change will have to be explained and documented as an alternative. Unless it becomes the default, I can't imagine uptake being large other than for internal use and with select customers who learn about it from us.

[Copilot]

Pull Request Overview

This PR introduces an "inproc" (in-process) mode for Golang functions, allowing the watchdog and function handler to run in a single process instead of spawning separate processes. This architectural change aims to reduce total RAM usage and potentially improve roundtrip latency for function invocations, with initial testing showing approximately 2-4 MB RAM usage compared to 11 MB for traditional separate-process mode.

Key changes:

• Adds new ModeInproc operational mode with corresponding configuration and executor
• Refactors main watchdog logic from main.go into pkg/watchdog.go to enable reusability
• Changes package structure from main to pkg for core watchdog components

Reviewed Changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
vendor/modules.txt	Adds google/uuid dependency for the new inproc mode
go.mod	Removes gorilla/mux from indirect dependencies
config/config_modes.go	Defines ModeInproc constant and adds "inproc" mode support
config/config.go	Adds Handler field and allows empty fprocess for inproc/static modes
config/config_test.go	Tests that inproc mode allows missing fprocess configuration
executor/inproc_runner.go	Implements InprocRunner for executing handlers in-process
pkg/watchdog.go	Refactored watchdog logic extracted from main.go into reusable package
main.go	Simplified to use new pkg.Watchdog with minimal bootstrapping code
requesthandler_test.go	Updates package from main to pkg and adjusts health handler calls
readiness_test.go	Updates package from main to pkg
readiness.go	Updates package from main to pkg

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[alexellis]

Reviewed by opencode / Big Pickle.. no significant issues detected.