Writing to a file in production with sinatra - ruby

Question

I cannot write to a file for the life of me using Sinatra in production.
In my development environment, I can use Logger without a problem and log STDOUT to a file.
It seems like in production, the Logger class is overwritten by the RACK middleware's Logger and it makes things more complicated.
I simply want to write to a file like this:
post '/' do
begin
$log_file = File.open("/home/ec2-user/www/logs/app.log", "w")
...do..stuff...
$log_file.write "INFO -- #{Time.now} --\n #{notification['Message']}"
...do..stuff...
rescue
$log_file.write "ERROR -- #{Time.now} --" + "\njob failed"
ensure
$log_file.close
end
end
The file doesn't get created when I receive a POST request to '/'.
However the file DOES get created when I load the app running pry:
pry -r ./app.rb
I am certain the code inside the POST block is effectively running because new jobs are getting added to the database upon receiving requests..
Any help would be greatly appreciated.

Answer 1

I was finally able to get to the bottom of this.
I changed the nginx user in /etc/nginx/nginx.conf from nginx to ec2-user. (Ideally I would just fix the write permissions for the nginx user but this solution suits me for now.)
Then I ps aux | grep unicorn and saw the timestamp next to the process name: unicorn master -c unicorn.rb -D was 3 days old!!
All this time I was pushing my code the the production server, restarting nginx and never killed and restart the unicorn process.
I removed all the code in my POST block and left only the file creation part
post '/' do
$log_file = File.open("/home/ec2-user/www/logs/app.log", "a")
$log_file.write("test log string")
$log_file.close
end
And the the file was successfully written to upon receiving a POST request.