IMGKit hangs when calling to_img(:jpg) method with rails s

[liqites]

Environment

ruby -> 2.0.0-p247
rails -> 4.0.13
OS X -> 10.10.4
imgkit -> 1.6.1
wkhtmltoimage -> 0.12.2.1

Start server with rails s

Using in Controller

def to_image
  html_string = render_to_string("images/index.html.erb") # a very simple page with a <p></p>
  kit = IMGKit.new(html_string)
  kit.to_file("tmp/xxx.kpg") #hangs here!!!
  ...
end

Additional Information

• Working if putting the code into Sidekiq job.
• Working if starting server using Unicorn with multiple workers. But single worker hangs!
• Working in Rails Console.

[liqites]

Sorry man, stupid question. I think reason is bellow:

• runing rails with rails s --> single process
• runing a child process with IMGKit to call command wkhtmltoimage
• wkhtmltoimage will load page, which means loading resource from rails server.
• but railsprocess is waiting wkhtmltoimage process to return to response my request.
• so no rails process can handle the wkhtmltoimage loading resource request.

Dead Lock, LOL

[phackwer]

I don't get it?! Is it solved? How?! I'm having similar problems here.

[liqites]

@phackwer That's because at that time, year 2015. My rails s only starts in single process mode.

Assumes that the only process called Process A, the progress will be like this:

1. Client send request --> Process A handle the request.
2. In Process A, it calls IMGKit to send another request to my rails server to render view for generating image and it waits.
3. Since Process A is waiting and I do not have another process to handle the IMGKit request.
4. My server hangs because of this.

Solution

You need to start your rails s server MULTIPLE PROCESSES or MULTIPLE THREADS mode

[phackwer]

Hi @liqites . Well, I'm using the Phusion/Passenger docker container (https://github.com/phusion/passenger-docker). How can I check if this is happening?

I'm having the most unusual problem here: when running a docker container locally in development mode, that has IMGKit, my code runs smooth, and generates the images properly. But when we go to the QA server, the QA hangs in the second request. wkhtmltoimage seems to get stuck, with no hope to ever come back. If I go into the docker container and kill the process manually (killall wkhtmltoimage-amd64) rails start responding other requests.

Now: what is really bizarre: if I call the endpoints that generate the images directly from my browser, al go, all normal... There is nothing special on the headers, actually it's a pretty standard get with the token in the URL, so there should be no problem at all with it!

Also, the same code that generates the images is used in a different part of our system (as we created it as a concern to be used on different controllers), and they are all working fine!!!

[liqites]

@phackwer

• If the reason your QA server hangs is not have enough process to handle requests.
• The easy way to determine the problem is calling the IMGKit code request an url not point to your system, like google.com, to generate image.
• If it still hangs, that's not the problem like mine.
• If it not hangs, that's maybe caused by lacking of enough processes.

Below is some more info I need to know for figuring out the question.

1. You said IMGKit code works smooth in locally development mode

My Question is:

• What url does your IMGKit code request to generate image ?
• Where does the url point to?
• Does the url point to an action in controller of your local development server? If so, it still has a chance of hangs. If not, then that is the reason why your local code works smooth.

2. QA server problem.

Question is:

• What url does your IMGKit code request to generate image ?
• Where does the url point to?
• Does the url point to an action in controller of your QA?
• How many processes or threads of your QA server?

I can't determine the answer without those information.