I have inherited the maintenance of a legacy web-application with an "interesting" way to manage concurrent access to the database.
The application is based on ruby-on-rails 2.3.8.
I'd like to set up a development environment and from there have two web browser make simultaneous requests, just to get the gist of what is going on.
Of course this is not going to work if I use Webrick, since it services just one http request at a time, so all the requests are effectively serialized by it.
I thought that mongrel could help me, but
mongrel_rails start -n 5
is actually spawning a single process and it seems to be single-threaded, too.
What is the easiest way of setting my development environment so that it responds to more than one request at a time? I'd like to avoid using apache and mod_passenger because, this being development, I'd like to be able to change the code and have it reloaded automatically on the next request.
In development mode, mod_passenger does reload classes and views. I use passenger exclusively for both development and deployment.
In production, you can (from the root of the rails app):
touch tmp/restart.txt
and passenger will reload the app.
Take a look at thin
http://code.macournoyer.com/thin/
Related
Hyperstack is an isomorphic framework where same code can run server or client side. So there are specific cases where depending on where some piece of code gets executed (server or client side) different things should be accomplished (client synchronization etc.).
The problem is that relying on the default check if
defined?(Rails::Server)
depends on the webserver you are running and the enclosing environment.
For example i run on puma (in docker for development and in Ubuntu server for production) and even in that case defined?(Rails::Server) works fine in development but not in production. This reveals that server execution detection depends not only on the actual server you are running on, but also on the method used to start it (e.x. rails s VS puma start)
Additional information can be found here:
Detect if application was started as HTTP server or not (rake task, rconsole etc)
https://gitter.im/ruby-hyperloop/chat?at=59d60f2201110b72317cd61c
https://hyperstack-org.slack.com/archives/CHRQ5U8HL/p1557262851049900
Is there a standard way to check whether something in Rails is executing on the server process/thread (not in browser, some sort of client, console, migration, rake task etc.) without relying on some hack to identify or declare what server we deploy on (puma, thin, nginx etc.)?
You can use the RUBY_ENGINE guard to see if the code is running in Opal or not.
if RUBY_ENGINE == 'opal'
# I am on the client
end
This is very useful in your Isomorphic models to exclude parts of the model's methods from existing on the client. Also very useful for using added Gem methods which make no sense in the client code.
In my application, I have used caching. This is the code, I have used. In after_filter, I called the method which include this one line code.
Rails.cache.write("properties", #properties.to_xml)
I try to get this in another action in before_filter like
#hotels = Rails.cache.fetch("properties")
this all working fine in development machine. But in server it returns null value. the application run in same development mode in server. Can you please anyone suggest me the right way. Thanks in advance.
It sounds like you haven't configured a backend for the store, so it will use ActiveSupport::Cache::MemoryStore
From the documentation:
If you're running multiple Ruby on Rails server processes (which is the case if you're using mongrel_cluster or Phusion Passenger), then this means that Rails server process instances won't be able to share cache data with each other.
This works in development since you are likely using a single server instance, so the cache is only stored in one process. For production you need to configure an alternative shared store. I'd recommend running a memcached instance, and installing and using the Dalli Gem as per the README.
This has been asked before, but never answered particularly exhaustively.
Let's say you have Rails running on one of the several web servers that support it, such as WEBrick, Mongrel, Apache and Nginx (through Passenger Phusion). The server receives two concurrent GETs, what happens? Is this clearly documented anywhere?
Basically I'm curious:
Is a new instance or rails is created by the server every time?
Does it somehow try to re-use existing instances (ruby processes with Rails already loaded in it?) to handle the request?
Isn't starting a new ruby process and re-loading Rails in it pretty slow?
Thanks! Any links to exhaustive clarifications would be greatly appreciated.
Some use workers (apache, phusion, unicorn), some don't. If you don't
use workers, it really depends wherever your application is threadsafe
or not. If you are, more than one request may be served at a time,
otherwise there's Rack::Lock which blocks that. If there are workers
(separate processes), each of them does a request then goes back to
the pool where the master assigns it a new request. Read
on
We have an environment running that uses Apache, Passenger and rails. The system is handling most request normally, yet certain requests do not make it to the rails application. For instance, a request to /books is successful, but /books/1 hits apache and passenger, but does not even make it to rails.
We set the apache log level to debug and the passenger log level to 3 so that we could monitor all incoming requests. We could see each request coming through and even the /books/1 request is being handled by passenger. But it never gets to rails.
Is there any way to determine where the request goes between Passenger and rails or where debugging information might live? Has anyone ever seen any problems with passenger spawning or queuing? We have spawning set to conservative. Also, we have had some permission/ownership problems in the past, so I am not ruling this out yet.
Thanks in advance
First guess: is that it's reading from your cache at public/books/1.html. This fits all the symptoms. If there is a public/books/1.html file when you go to request books/1 Apache will serve the request by sending just that file.
Second guess: alternate configuration is mucking about with how Apache is serving the route.
I'd like to know why is there a need to restart the server (Mongrel/WEBrick) every time a model file is updated? I know it doesn't get loaded in if you don't do it - but is there any documentation out there that would explain why it does so?
Thanks!
Development environments do not require you to restart the server if you change a model. They will reload the environment for each request if necessary.
Production environments are a different story. A Rails server (mongrel/passenger/webrick/etc) running in a production environment will only load your Rails environment once when the process is started. This takes a couple of seconds, as you might notice when starting the console which also loads your Rails environment. To avoid this overhead for each request the server will spawn a new thread from the loaded environment to handle each incoming request.
Because the server only responds to HTTP requests, and the usual signals. There's no good way to force an environment reload beyond always loading a fresh environment (like a development environment, or restarting the server.