Cloud Functions Simple(st) HTTP Multi-host Proxy

September 18, 2019 - 2 minutes read - 353 words

Tweaked yesterday’s solution so that it will randomly select one from several hosts with which it’s configured.

package proxy

import (
	"log"
	"math/rand"
	"net/http"
	"net/url"
	"os"
	"strings"
	"time"
)

func robin() {
	hostsList := os.Getenv("PROXY_HOST")
	if hostsList == "" {
		log.Fatal("'PROXY_HOST' environment variable should contain comma-separated list of hosts")
	}
    // Comma-separated lists of hosts
    hosts := strings.Split(hostsList, ",")
    
    urls := make([]*url.URL, len(hosts))
    for i, host := range hosts {
		var origin = Endpoint{
			Host: host,
			Port: os.Getenv("PROXY_PORT"),
		}
		url, err := origin.URL()
		if err != nil {
			log.Fatal(err)
		}
		urls[i] = url
	}

	s := rand.NewSource(time.Now().UnixNano())
	q := rand.New(s)

	Handler = func(w http.ResponseWriter, r *http.Request) {
		// Pick one of the URLs at random
		url := urls[q.Int31n(int32(len(urls)))]
		log.Printf("[Handler] Forwarding: %s", url.String())
        // Forward to it
        reverseproxy(url, w, r)
	}
}

This requires a minor tweak to the deployment to escape the commas within the PROXY_HOST string to disambiguate these for gcloud:

FUNCTION=multi
gcloud functions deploy ${FUNCTION} \
--entry-point=Handler \
--runtime=go111 \
--set-env-vars=^:^PROXY_HOST=${NODEHOSTS}:PROXY_PORT=${NODEPORT} \
--trigger-http \
--project=${PROJECT}

NB The --set-env-vars flag is followed by ^:^ to denote the command uses : instead of , because the value of ${HOSTS} contains commas

How to get the list of hosts? Assuming

SERVICE=nginx
NODEPORT=$(\
  kubectl get service/${SERVICE} \
  --output=jsonpath="{.spec.ports[0].nodePort}")

TAG=$(\
  gcloud compute instances list \
  --project=${PROJECT} \
  --format="value(tags.items)" \
  | shuf --head-count=1) \
&& echo ${TAG}

FIREWALL=lb
gcloud compute firewall-rules create ${FIREWALL} \
--project=${PROJECT}  \
--network=default \
--action=ALLOW \
--rules=tcp:${NODEPORT} \
--target-tags=microk8s

NODEHOSTS=$(\
  gcloud compute instances list \
  --project=${PROJECT} \
  --filter="tags.items=${TAG}" \
  --format="value(networkInterfaces[0].accessConfigs[0].natIP)" \
  | tr '\n' ',' \
  | sed 's|,*$||g') \
&& echo $HOSTS

NB This is hacky because it picks a tag randomly from the project’s instances’ tags

Once deployed:

ENDPOINT=$(\
  gcloud functions describe ${FUNCTION} \
  --project=$PROJECT \
  --format="value(httpsTrigger.url)")
  curl \
  --silent \
  --write-out "%{http_code}" \
  --output /dev/null \
  ${ENDPOINT}

Attempting to determine how efficient the process is:

gcloud logging read "resource.type=\"cloud_function\" resource.labels.function_name=\"${FUNCTION}\"" \
--project=$PROJECT \
--freshness=1d \
--format=json \
| jq --raw-output .[].textPayload \
| egrep -o "\[Handler\] Forwarding: http://[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}.[0-9]{1,3}:30536" \
| awk '{print $3}' \
| sort \
| uniq -c
    103 http://HOST-1:30536
    124 http://HOST-2:30536
    105 http://HOST-3:30536

So, not bad ;-)

Golang
GRPC