Creating a variable per instance, rather than per request, with Sinatra modular style - ruby

Question

I have a Sinatra app, written in modular style, running on Heroku. It uses Redis and I have a limited number (10) of Redis connections. I found that it would often throw errors complaining that it had run out of Redis connections. So I started using connection_pool in the hope that would fix things; a single pool of Redis connections and the app would choose one of those each time, rather than try to create a new connection on each request.
But I'm still getting the same issue. I can do loads of Redis queries on a single query without complaints. But if I reload a single test page, which just does some Redis queries, several times in fairly quick succession, I get the "Redis::CommandError - ERR max number of clients reached" error again.
So I'm assuming, maybe, it's creating a new instance of connection_pool on each request... I don't know. But it's not "pooling" as I would expect it to.
I have this kind of thing:
# myapp.rb
$LOAD_PATH.unshift(File.dirname(__FILE__))
$stdout.sync = true
require 'thin'
require 'myapp/frontend'
MyApp::Frontend.run!
And the Sinatra app:
# myapp/frontend.rb
require 'sinatra/base'
require 'redis'
require 'connection_pool'
require 'uuid'
module MyApp
class Frontend < Sinatra::Base
helpers do
def redis_pool
#redis_pool ||= ConnectionPool.new(:size => 8, :timeout => 5) do
redis_uri = URI.parse(ENV['REDISCLOUD_URL'])
client = ::Redis.new(:host => redis_uri.host,
:port => redis_uri.port,
:password => redis_uri.password)
end
end
end
get '/tester/'
redis_pool.with do |r|
id = UUID.generate
r.hset(:user, id, "Some data")
r.hget(:user, id)
r.hdel(:user, id)
end
p "DONE"
end
end
end
The Procfile looks like:
web: ruby myapp.rb
Any ideas? The current site is pretty low traffic, so this should be possible.

Answer 1

A new instance of #redis_pool is created every time a get request for /tester/ is processed because the helper method redis_pool is called every time.
You can use sinatra's settings helper to initialize a redis connection only once:
config do
redis_uri = URI.parse(ENV['REDISCLOUD_URL'])
set :redis, Redis.new(:host => redis_uri.host,
:port => redis_uri.port,
:password => redis_uri.password)
end
Now the each instance of the app has one redis connection that persists for all requests. Access the setting like so
get '/tester/'
id = UUID.generate
settings.redis.hset(:user, id, "some data")
settings.redis.hget(:user, id)
settings.redis.hdel(:user, id)
p "DONE"
end