I am working on a multiple projects that talk to each other sometimes and I've run into an issue where app
A calls B (request 1, still running)
B calls A (request 2)
based on request 2's result, B responds to request 1
This requires me running multi-threaded rails in development mode.
I know I can set it up using puma or something like that but ... Isn't there really a simpler way?
I would like to avoid changing anything in the project (adding gems, config files..).
Something like rails s --multi would be nice, can't webrick just run with multiple threads or spawn more processes?
Can I perhaps install a standalone gem to do what I need and run something like thin run . -p 3?
The puma web server can provide multi-threading and multiple workers bound to a single local address.
Install the puma gem:
bundle add puma
or
gem install puma
Add a puma configuration file at config/puma.rb:
workers 1 # 1 worker in addition to master instance (i.e. handle 2 requests concurrently).
preload_app!
Launch the Rails server.
bundle exec rails s
Puma automatically starts and loads in the config file at config/puma.rb.
Bump up the value for workers if you need to handle more than 2 concurrent requests at the same time.
One way to solve this is to use POW, which uses two workers by default.
The nice thing is I don't have to modify the project files to do it so it satisfies my requirements.
Update: The up to day successor of POW is puma-dev, which is also zero-configuration.
My current solution, that's super kludgy, is to use Foreman and a Procfile to run two copies of my app on different ports. You'd have to configure your B service to make requests to the secondary port.
Related
For example, in PHP-based apps it's recommended to run PHP-FPM from a user different from the user who owns codebase so if anyone hacks your app from the web won't be able to write anything to a codebase (except public assets directory). It seems like ruby apps designed to run HTTP servers (or application/rake servers) like Unicorn and Puma from the same user. Puma (the default rails server) doesn't even have config entries for specifying a user/group.
UPDATE
What I expect to do with a ruby app (the same I do with PHP-FPM) is to run sudo unicorn or sudo puma from a default user (codebase owner) and specify a user/group (like www-data) in config so the HTTP server will run the master process from root and child processes from www-data. Puma has no such settings and I haven't found any related issues in puma's repo. This made me think that maybe it's a common thing in Ruby ecosystem to run it like that. I still tried to run latest rails app (5.2.1) with unicorn but faced another issue: rails has a dependency on bootsnap gem and when you run sudo unicorn -c config.rb it creates tmp/cache/bootsnap-* directories as root (in master process) which breaks everything because child processes running from www-data won't have access to it. That made me consider again that maybe I'm doing something wrong and it's ok to run ruby apps from codebase-owner although I see no arguments how it's different from running PHP-FPM.
I need to run a command after or before starting Rails. It will start a server on port 9292 so my chat app will work.
This command should preferably be executed automatically with Rails (on production and development).
How do we do that in Rails 4?
Is Capistrano the only option? Can we schedule it to be executed when Rails starts?
Use capistrano and forman or systemd to manage your chat server instance, like, for example you would do for sidekiq.
A good start would be : http://anlek.com/2015/01/using-foreman-with-upstart-capistrano/
You have 2 options that I know of if you don't want to use Capistrano. In your config/application.rb
config.after_initialize do
# ....
end
http://guides.rubyonrails.org/configuring.html
or you can write a custom initializer that is run with on_server_start event.
There's a whole section of config/ intended for startup behavior: config/initializers/. If you need to do anything as part of the startup of your app, you can create an initializer file here, and it will automatically get run as Rails starts.
To do this, simply create a new file: config/initializers/chat_app.rb:
# This file will start and establish an initial connection to the chat app
`chat-app --some-arg` # <== The chat app
We use this for various startup and system sanity checks for the application. It's independent of your deployment, so if you need it for other deployment purposes, creating a Capistrano (or even Rake) task is the better option.
It's nice to see Rails 4.2 come with Active Job as a common interface for background jobs. But I can't find how to start a worker in the document. It seems that the document is still immature (e.g. the right version of Sneakers is only referred to in Rails' Gemfile), so I'm not sure if the "running workers" part is not in Active Job or just not mentioned in docs.
So with Active Job, do I still need to manually start the job watcher threads like sidekiq or in my case, rake sneakers:run? If so, where should I put these commands to let rails server run these parallel tasks automatically in a develop environment?
ActiveJob is just a common interface. You still need the backend gem, and you still need to launch it separately from your server (it is a separated process, which is the objective).
Sample using resque:
In the Gemfile:
gem 'resque'
In the terminal, launching a worker:
bin/resque work
The case is similary when using sidekick, delayed job or something else.
If you want to launch the server & worker in a single command, you can create a short bash script for it, but I would advise not doing so: having two separated console helps to watch what is happening on each side (web app & worker).
A better solution would be to use the foreman gem to manage starting & stopping your process.
You can create a simple Procfile with the processes to start:
web: bundle exec rails s
job: bundle exec resque work
And then just start both using foreman:
foreman start
By default, foreman will interleave the logs of the process in the console, but this can be configured.
You still have to run the job thread watcher.
I'm using EventMachine and Monetarily to start e TCP server along with my rails application. This is started from config/initializers/momentarily.rb.
My problem is that it starts also when I run rake tasks, like db:migrate. I only want it to start when when I start the HTTP server. Environments won't help, since both the server start and rake tasks are under Development environment. Is there a way of knowing that the application is running the HTTP server as opposed to anything else? Note that is not only rake tasks, the EM starts also if I run the rails console, which is again something not desirable for my case.
unless File.basename($0) == "rake" && ARGV.include?("db:migrate")
# you are not in rake db:migrate
end
There's not a great way of doing this that I know of. You could copy newrelic's approach (check discover_dispatcher in local_environment.rb) which basically has a list of heuristics used to detect if it is running inside passenger, thin, etc.
For passenger it checks
defined?(::PhusionPassenger)
for thin it checks
if defined?(::Thin) && defined?(::Thin::Server)
Set an environment variable in config.ru file, and use it anywhere in the code to detect if it's executed using a rails server command only.
For e.g.
File: config.ru
ENV['server_mode'] = '1'
And using it somewhere as:
File: config/environment.rb
Thread.new { infinite_loop! }.join if ENV['server_mode'] = '1'
Reference: Answer
Maybe you can implement a switch in the initializer based on ARGV?
Something like:
if ARGV.join(' ').match /something/
# your initializer code here
end
Don't start that other server from an initializer. Create a daemon in script/momentarily and start it from within your app.
After your application launches, you could have it shell out to check ps. If ps shows that the HTTP server is running and the running HTTP server has the same pid as your application (check the pid by inspecting $$), then you could launch the TCP server.
In addition to a great answer by Frederick Cheung above, there can be some other "footprints" in actual process environment. Eg. Phusion Passenger adds certain variables to ENV such as:
PASSENGER_APP_ENV
IN_PASSENGER
PASSENGER_SPAWN_WORK_DIR
PASSENGER_USE_FEEDBACK_FD
Web servers typically can also set SERVER_SOFTWARE variable eg.:
SERVER_SOFTWARE=nginx/1.15.8 Phusion_Passenger/6.0.2
I need to setup a connection to an external service in my Rails app. I do this in an initializer. The problem is that the service library uses threaded delivery (which I need, because I can't have it bogging down requests), but the Unicorn life cycle causes the thread to be killed and the workers never see it. One solution is to invoke a new connection on every request, but that is unnecessarily wasteful.
The optimal solution is to setup the up the connection in an after_fork block in the unicorn config. The problem there is that doesn't get invoked outside of unicorn, which means we can't test it in development/testing environments.
So the question is, what is the best way to determine whether a Rails app is running under Unicorn (either master or worker process)?
There is an environment variable that is accessible in Rails (I know it exists in 3.0 and 3.1), check the value of env['SERVER_SOFTWARE']. You could just put a regex or string compare against that value to determine what server you are running under.
I have a template in my admin that goes through the env variable and spits out its content.
Unicorn 4.0.1
env['SERVER_SOFTWARE'] => "Unicorn 4.0.1"
rails server (webrick)
env['SERVER_SOFTWARE'] => "WEBrick/1.3.1 (Ruby/1.9.3/2011-10-30)"
You can check for defined?(Unicorn) and in your Gemfile set: gem :unicorn, require: false
In fact you don't need Unicorn library loaded in you rails application.
Server is started by unicorn command from shell
Checking for Unicorn constant seems a good solution, BUT it depends very much on whether require: false is provided in the Gemfile. If it isn't (which is quite probable), the check might give a false positive.
I've solved it in a very straightforward manner:
# `config/unicorn.rb` (or alike):
ENV["UNICORN"] = 1
...
# `config/environments/development.rb` (or alike):
...
# Log to stdout if Web server is Unicorn.
if ENV["UNICORN"].to_i > 0
config.logger = Logger.new(STDOUT)
end
Cheers!
You could check to see if the Unicorn module has been defined with Object.constants.include?('Unicorn').
This is very specific to Unicorn, of course. A more general approach would be to have a method which sets up your connection and remembers it's already done so. If it gets called multiple times, it just returns doing nothing on subsequent calls. Then you call the method in after_fork and in a before_filter in your application controller. If it's been run in the after_fork it does nothing in the before_filter, if it hasn't been run yet it does its thing on the first request and nothing on subsequent requests.
Inside config/unicorn.rb
Define ENV variable as
ENV['RAILS_STDOUT_LOG']='1'
worker_processes 3
timeout 90
and then this variable ENV['RAILS_STDOUT_LOG'] will be accessible anywhere in your Rails app worker thread.
my issue:
I wanted to output all the logs(SQL queries) when on the Unicorn workers and not on any other workers on Heroku, so what I did is adding env variable in the unicorn configuration file
If you use unicorn_rails, below code will help
defined?(::Unicorn::Launcher)