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This application is split into two distinct components, the mshots PHP class (receiving requests from the WordPress mshots plugin), the node.JS cluster service to process the filtered incoming requests passed on from the mshots class. Note: The virtual frame buffer Kernel module (VFB) is required for the service.

Production Installation

These instructions are for setting up mShots for production on a linux host. If you only need to run mShots locally skip down to the Dev Setup.

If anything goes awry or is unclear in one of these steps, take a look at the "Details" section below for slightly more detailed info.

  1. Install the latest node.js binaries from

  2. Place the code in this repository in an mshots folder in /opt/, so the final path is /opt/mshots/.

  3. Run npm install --ignore-scripts in the /opt/mshots/ directory.

  4. You are now ready to run the mshots service with "./ start|stop". Note: The virtual frame buffer Kernel module (VFB) is required on your distro.

Production Deployment

The Automattic Systems Team manages the live deployment of mShots. Once a PR has been reviewed, merge it into master and then make a systems request to have the change deployed. Try to include isolated testing instructions for the PR (i.e. that don’t require using Calypso or and screenshots to show the expected visual results.


The mshots PHP Class (code in "public_html")

This class is designed to buffer the thumbnail requests, by limiting snapshots to only be taken every 24 hours. The most useful attribute of this class is the "disable_requeue" constant, but changing this to true you effectively stop all calls to the mshots service, which can be used if the service misbehaves for any reason. With this setting enabled existing thumbnails will be served, but no new thumbnails are generated.

mshots node.JS Program (code in "lib")

Control the execution of the application with the bash script in the root directory or by manually running the following command from the terminal, whilst in the /opt/mshots/ directory:

> node lib/mshots -p <port number> -n <number of workers>


Both JS and php unit tests live in the tests directory and can be run with the npm test command.

They can also be run individually with npm run test:js and npm run test:php

The test scripts should also work inside the docker container described immediately below.

Dev Setup

Docker can be used to run the mshots service on OSX for dev/testing purposes:

  • First, give docker permission to mount your dev directory. For Docker Desktop this is in Preferences -> Resources-> File Sharing where you can add the path to where mshots is checked out.
  • npm install: This will also configure the docker container for development and build the docker image (unless you pass --ignore-scripts)
  • npm start: spins up the mshots (docker) service in the mshots-dev container and starts the mshots (*nix) service within it
  • Ignore the errors about the missing commands. We don't use the kernel extension in the dev container.
  • Check that mshots is available on localhost:8000, e.g. http://localhost:8000/mshots/v1/

Note that when you enter a new url for the first time, mShots will redirect to while it fetches the url and generates the screenshot. Wait a few seconds and navigate to the url a second time to see the generated image.

Note that output is a bit tricky.

While docker is running you can use docker-compose logs to attach and get it's output, which covers php and mshots.ctl and general docker/apache output.

As a service, mShots doesn't have a parent terminal and also has minimal file permissions so use logger.debug( 'msg' ) and logger.error( 'msg' ), which dump output into /opt/mshots/logs/mshots.log.

If you need debug ouput from a dependency (like puppeteer), you can give the file write permissions: chmod a+w logs/mshots.log and then append to that (or another) file: fs.appendFileSync( 'logs/mshots.log', '\n' + JSON.stringify( { whatever: [ 'data' ] }, null, 2 ) + '\n' )

Performance testing

Performance tests live in scripts/performance-test and use the locust python framework. See Performance testing readme


Error response from daemon: Mounts denied

This occurs if docker does not have permissions to mount your local development directory into the container. Follow the given instructions to resolve this - for Docker Desktop, add the path under Docker -> Preferences... -> Resources -> File Sharing.

Missing chromium binary

The container requires a linux chromium binary, so if puppeteer can't find chromium, run install.js in the puppeteer directory in the appropriate environment. Binaries for different OSes can live side-by-side so you can just install both:

# check what's already installed
ls /opt/mshots/node_modules/puppeteer/.local-chromium
# install native binary
(cd /opt/mshots/node_modules/puppeteer; node install.js)
# install linux binary in container
docker-compose exec dev bash -c 'cd node_modules/puppeteer; node install.js'

The local /opt/mshots directory is mounted into the container, so code changes are immediately reflected in the container and generated images will appear under /opt/mshots/public_html/thumbnails in the container and ./public_html/thumbnails relative to your local repo.

The purpose of the container is to provide the linux service environment used by (particularly start-stop-daemon), and the javascript generally works inside or outside the container or both.

Permission errors

You can get get a root shell docker-compose exec -u 0 dev bash, or change the user in the image & container permanently by modifying the UID in /opt/mshots/.env file and re-running docker-compose build.

Background: Docker containers share the kernel with the docker host (the machine that dockerd is running on - physical or virtual). Of particular note is that this means that the same UIDs drive file permissions inside and outside the container.

This means that you'll want to have the same UID inside the container that you used to create your local files. Normally, this will be set up automatically when you npm install locally, but some docker setups may mess with your user IDs (e.g. running dockerd in a VM through docker-machine).

It's the uid that matters, not the username, so use id -u <username> inside the container to find the right value. stop doesn't work

I'm not sure why stop doesn't work in the container, but you can emulate it with the npm run stop command.


npm ERR! nospc ENOSPC: no space left on device, mkdir '/var/www/.npm/_cacache'
npm ERR! nospc There appears to be insufficient space on your system to finish.
npm ERR! nospc Clear up some disk space and try again.

Try docker image prune to remove old images.