Autoscale NGINX and PHP-FPM independently on Google Kubernetes Engine

Let’s say I have a stateless php app that needs to run 24/7 and automatically scale up to perform well and scale down to be cost-effective. Perfect use case for Kubernetes, right? (Let’s be honest here now — you would use Kubernetes anyway because all the cool kids do it these days).

Cool then, let’s start the naive way —

Solution 1:

FROM debian
RUN apt-get update && apt-get -y install nginx php-fpm

Ok ok, let’s just forget about this and start a bit better, shall we?

Solution 2:

Separate the nginx a php-fpm into two images

FROM nginx:1.13
COPY src/ /code/
COPY site.conf /etc/nginx/conf.d/default.conf

server {

index index.php index.html;

server_name localhost;

error_log /var/log/nginx/error.log;

access_log /var/log/nginx/access.log;

root /code/;

location ~ \.php$ {

try_files $uri =404;

fastcgi_split_path_info ^(.+\.php)(/.+)$;

fastcgi_pass localhost:9000;

fastcgi_index index.php;

include fastcgi_params;

fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;

fastcgi_param PATH_INFO $fastcgi_path_info;

}

}

Then build the php image

FROM php:7.1-fpm
COPY src/ /code/

Now make a simple kubernetes deployment with two containers — nginx and php, the communicate via the pod’s shared network using tcp port 9000(fastcgi_pass localhost:9000)

Great, now we can scale horizontally and vertically with ease. Just set the number of replicas and create a horizontal pod autoscaler. Don’t forget to set the containers’ cpu/mem quotas.

But wait. What if my php app is very cpu intensive in peaks and I need to run a lot of php replicas but nginx, on the other hand, just handles a couple of requests and two/three replicas are more than enough just to satisfy the HA needs?

Problem 1:

Horizontal scaling scales both php and nginx, even if only one of them needs to be scaled out.

Problem 2:

What is more, I need to build two docker images with the same application code. That just doesn’t seem right. Deployments/rollbacks need to change both image tags at the same time otherwise we have an undefined state. And god kills a kitten.

Solution 3:

Nginx doesn’t know php. There is no need to have the src/ in nginx image. Let’s use the standard nginx image and put the source code in php image only.

We had one pod with both nginx and php, now we want both of them have their own pod. Make two kubernetes deployments and kubernetes service for php pods.

FROM nginx:1.13
COPY site.conf /etc/nginx/conf.d/default.conf

since the php script are no longer in nginx, delete the try_files directive, next change the fastcgi_pass to the kubernetes service’s local dns (I named it php):

#try_files $uri =404;
fastcgi_pass php:9000;

The kubernetes service called php loadbalances tcp traffic internally between pods labeled php. A local dns record php is created automatically for that internal loadbalancer. Nginx now sends the requests to the balanced pods group.

Now we can scale nginx and php-fpm independently and the app code is in php image only.

 

check the php logs for loadbalancing:

 

Solution 4:

Is there a better solution for GKE?

Is it a bad idea to get rid of the try_files in nginx.conf? Should I even use nginx at all? (let’s assume I’m serving the static assets from a different source)

How does this work? Why am I getting nginx’s IP address with this —

<?php echo $_SERVER[‘SERVER_ADDR’]; ?>

Feel free to discuss this with me, I’m having a hard time finding anything useful for running php on GKE. Would be nice to get hands on some best practices! Drop me a message at mab@revolgy.com.