A PHP fpm Health Check script

With the ascension of containerized applications it becomes more and more useful to have a php-fpm healthcheck.

This POSIX compliant sh script gets php-fpm status page using cgi-fcgi tool, parses it's outcome and allows you to choose a metric which you want to check one, a ping mode is also available which only makes sure php-fpm is answering.

• Motivation
• Installation
• Usage
• Docker example
• Kubernetes example
• Why POSIX sh?
• Author and License

Motivation

Previously at work we had Docker containers containing both php-fpm and Nginx processes, while they were managed by another process being Supervisord or s6 overlay for instance. One good example is this image from Ric Harvey

It works really well, but I wanted to achieve a few other things like using the official images and its release cycle, logs belonging to their own processes, not mixed, I didn't like to rely on Supervisord since I had bad experiences in the past with it, and other things related to the "Docker way", I'm not saying it's perfect but I wanted some of those things.

Now comes the php-fpm healthcheck part, while having in place a healthcheck which requested an url in the application asking if it was alive, it was indirectly testing the whole chain, Nginx -> php-fpm -> application, and now I had the chance to test still the whole chain via nginx but also monitor how busy and stable is php-fpm, if you check its /status page it has quite some useful information, so why not monitor on it? For instance you could make a container unhealthy after a certain amount of requests, or if the queue is too long and even slow requests, and that's what this script tries to achieve!

Good news is that you can still do it even using the mixed container approach, but I wanted to take a time to explain why I came to do it like this now! The advantage in my opinion is that having separate containers you have a better grasp on where the problem is laying and you can restart only what's failing, not the whole, also avoiding Supervisord to restart it for you since you are already behind a container orchestration tool.

Installation

Enable php-fpm status page

On you php-fpm pool configuration add: pm.status_path = /status

For instance on the official php image you can alter the file /usr/local/etc/php-fpm.d/zz-docker.conf

See a simple example

More about PHP fpm pool configuration

Requirements

The script is POSIX sh but also uses some tools from your operating system, being:

• cgi-fcgi
• sed
• tail
• grep

In case you're using alpine you only need to make sure you have installed busybox and fcgi packages.

See a simple Dockerfile based on the official PHP image

Download

wget -O /usr/local/bin/php-fpm-healthcheck \
https://raw.githubusercontent.com/renatomefi/php-fpm-healthcheck/master/php-fpm-healthcheck \
&& chmod +x /usr/local/bin/php-fpm-healthcheck

Update

wget -O $(which php-fpm-healthcheck) \
https://raw.githubusercontent.com/renatomefi/php-fpm-healthcheck/master/php-fpm-healthcheck \
&& chmod +x $(which php-fpm-healthcheck)

Manually

You can always of course manually download and maintain the file, as long as you follow the MIT License

Usage

Ping mode

If you're aiming only to make sure php-fpm is alive and answering to requests you can:

$ php-fpm-healthcheck
$ echo $?
0

Or with verbose to see php-fpm status output:

$ php-fpm-healthcheck -v
Trying to connect to php-fpm via: localhost:9000/status
php-fpm status output:
pool:                 www
process manager:      dynamic
start time:           11/Sep/2018:10:47:06 +0000
start since:          436
accepted conn:        1
listen queue:         0
max listen queue:     0
listen queue len:     0
idle processes:       1
active processes:     1
total processes:      2
max active processes: 1
max children reached: 0
slow requests:        0
$ echo $?
0

Metric mode

Let's say you want to fail our healthcheck after your fpm has handled more than 3000 requests:

$ php-fpm-healthcheck --accepted-conn=3000
$ echo $?
0

And you can also check if you have more than 10 processes in the queue:

$ php-fpm-healthcheck --accepted-conn=3000 --listen-queue=10
$ echo $?
0

How a failing metric looks like

$ php-fpm-healthcheck --accepted-conn=1
'accepted conn' value '6' is greater than expected '1'
$ echo $?
1

Connection via socket or another host

You can simply specify FCGI_CONNECT variable with your connection uri:

$ FCGI_CONNECT=/var/run/php-fpm.sock php-fpm-healthcheck
$ echo $?
0

Alternative status page path

Since v0.5.0

While the default status page path is /status, you can replace it in your php-fpm configuration, in order to change also in the script in you can specify FCGI_STATUS_PATH env var within your connection uri:

$ FCGI_STATUS_PATH=/custom-status-path php-fpm-healthcheck -v
Trying to connect to php-fpm via: localhost:9000/custom-status-path
...
$ echo $?
0

Docker example

You can use HEALTHCHECK command on Dockerfile to define the health of your container. According to Docker Docs, possible return values are 0 for success, 1 to unhealthy and 2 is reserved and we must not use this exit code.

HEALTHCHECK --interval=5s --timeout=1s \
    CMD php-fpm-healthcheck || exit 1

Kubernetes example

More and more people are looking for health checks on kubernetes for php-fpm, here is an example of livenessProbe and readinessProbe:

livenessProbe

# PodSpec: https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.10/#podspec-v1-core
    spec:
        containers:
        - name: "php-fpm"
        livenessProbe:
            exec:
                command:
                    - php-fpm-healthcheck
                    - --listen-queue=10 # fails if there are more than 10 processes waiting in the fpm queue
                    - --accepted-conn=5000 # fails after fpm has served more than 5k requests, this will force the pod to reset, use with caution
            initialDelaySeconds: 0
            periodSeconds: 10

readinessProbe

# PodSpec: https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.10/#podspec-v1-core
    spec:
        containers:
        - name: "php-fpm"
        readinessProbe:
            exec:
                command:
                    - php-fpm-healthcheck # a simple ping since this means it's ready to handle traffic
            initialDelaySeconds: 1
            periodSeconds: 5

Docker HEALTHCHECK command is ignored on Kubernetes and you must define it using pod specifications.

Why POSIX sh

Most of the containers contain limited software installed, using POSIX sh aims to be compatible with most of the OS images around.

Author

Made with love by Renato Mefi

Distributed under MIT License