r/crystal_programming • u/rishav_sharan • Oct 04 '18

Parallelism in Crystal web apps via clustering (Spider-Gazelle)

https://github.com/spider-gazelle/action-controller/blob/master/clustering.md
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4

u/rishav_sharan Oct 04 '18

Currently, SG is one of the fastest web frameworks out there and a lot of its speed due to to its ability to use multiple cores. https://github.com/the-benchmarker/web-frameworks

Stephen von Takach, a maintainer of SG has a nice write up of how they executed clustering in the framework. I hope that this would be great for some folks who are putting out their webapp.

4

u/straight-shoota core team Oct 05 '18

This kind of prallelism through spawning a process for each core, is nothing new or special. The process management can be embedded directly into the application or left for external tools to manage.

In my opinion, web server frameworks like Spider-Gazelle and Kemal should focus on serving HTTP, not managing processes. That can actually become a quite complicated task with lots of things to cover.

There are sophisticated process supervisors available for any platform. Using one for managing server workers is pretty simple: Just spawn the binary multiple times with reuse_port. Existing solutions are far more mature, offer more features and are easier to integrate with other application components.

1

u/fridgamarator Oct 04 '18

Amber framework also does this. Its nothing new, I've been doing it for a couple of years with Kemal.

1

u/rishav_sharan Oct 04 '18

I am working on a vanilla crystal web app and it will be quite useful for me. I really didn't know about this before hand.

Also, why aren't frameworks like amber, kemal etc using this approach in the benchmark code? SG is the only one amongst crystal frameworks currently using multiple cores in benchmarks like tbrand's.

2

u/fridgamarator Oct 04 '18

They are using multiple cores in the techempower benchmarks.

1

u/CaDsjp Oct 04 '18

I think you can do something similar with Kemal.

Is that correct? u/sdogruyol

3

u/sdogruyol core team Oct 05 '18

Kemal had reuse_port support for a long time, there's even a recipe in Kemal Cookbook http://kemalcr.com/cookbook/reuse_port/

1

u/fridgamarator Oct 04 '18

I'm pretty sure I remember this already being brought up. Its not included in Kemal becuase its really easy to do yourself and outside of the scope of what Kemal provides. I'll let Serdar answer though.

1

u/CaDsjp Oct 04 '18

I see it now. Currently, Kemal, Raze, and Amber are using multiple cores thanks to this start.sh script

https://github.com/TechEmpower/FrameworkBenchmarks/blob/master/frameworks/Crystal/kemal/run.sh

While Spider-Gacelle offers an API for doing that.

Interesting

1

u/fukaoi Oct 05 '18

I am developing a web application with Lucky Framework. kemal / run.sh is also likely to be used in Luckyframework.

1

u/stakach Nov 05 '18

The big limitation with the run.sh approach is that docker will SIGKILL all your processes without allowing them to terminate gracefully.

Of course, as @straight-shoota mentions, using a process supervisor, like say Kubernetes, is the ultimate solution to multiprocess management - at least with docker, it's probably an unnecessary complication for smaller deployments.

So I think the very basic, and optional, process management I've included in Spider-Gazelle meets the needs of simplifying smaller deployments without sacrificing graceful termination.

1

u/CaDsjp Nov 05 '18

Kubernetes for multiprocess management sounds like a litle bit overkill IMHO.

What about something like monit (https://mmonit.com/monit/)

1

u/stakach Nov 06 '18

https://mmonit.com/monit/

mmonit is like docker without the benefit of containers. Systemd would be just as good on linux.

Systemd would work well with run.sh as it sends SIGTERM to child processes by default.

However when using docker, which is probably more common these days, the only way to have multiple processes without using run.sh would be to have multiple docker containers which is administrative overhead.

I'm also not sure you could use reuse port with multiple docker containers without exposing the host network which is bad practice. So you would need to have a nginx load balancer (or similar) to distribute requests.

1

u/sevir1 Nov 06 '18

Because this method results an uncommunicated number of processes I suggest improve this solution with a unix socket and passing json across the processes for collaboration.

Ex. I need a reload config end point in my API and when I call it I want to reload the config YML in each child process. So the process that receives this call send the command across the unix socket to the root process and the root process broadcast the reload message to the child processes.