How to improve Nginx, Rails, Passenger memory usage? - ruby-on-rails

Question

I currently have a rails app set up on a Digital Ocean VPS (1GB RAM) trough Cloud 66. The problem being that the VPS' memory runs full with Passenger processes.
The output of passenger-status:
# passenger-status
Version : 4.0.45
Date : 2014-09-23 09:04:37 +0000
Instance: 1762
----------- General information -----------
Max pool size : 2
Processes : 2
Requests in top-level queue : 0
----------- Application groups -----------
/var/deploy/cityspotters/web_head/current#default:
App root: /var/deploy/cityspotters/web_head/current
Requests in queue: 0
* PID: 7675 Sessions: 0 Processed: 599 Uptime: 39m 35s
CPU: 1% Memory : 151M Last used: 1m 10s ago
* PID: 7686 Sessions: 0 Processed: 477 Uptime: 39m 34s
CPU: 1% Memory : 115M Last used: 10s ago
The max_pool_size seems to be configured correctly.
The output of passenger-memory-stats:
# passenger-memory-stats
Version: 4.0.45
Date : 2014-09-23 09:10:41 +0000
------------- Apache processes -------------
*** WARNING: The Apache executable cannot be found.
Please set the APXS2 environment variable to your 'apxs2' executable's filename, or set the HTTPD environment variable to your 'httpd' or 'apache2' executable's filename.
--------- Nginx processes ---------
PID PPID VMSize Private Name
-----------------------------------
1762 1 51.8 MB 0.4 MB nginx: master process /opt/nginx/sbin/nginx
7616 1762 53.0 MB 1.8 MB nginx: worker process
### Processes: 2
### Total private dirty RSS: 2.22 MB
----- Passenger processes -----
PID VMSize Private Name
-------------------------------
7597 218.3 MB 0.3 MB PassengerWatchdog
7600 565.7 MB 1.1 MB PassengerHelperAgent
7606 230.8 MB 1.0 MB PassengerLoggingAgent
7675 652.0 MB 151.7 MB Passenger RackApp: /var/deploy/cityspotters/web_head/current
7686 652.1 MB 116.7 MB Passenger RackApp: /var/deploy/cityspotters/web_head/current
### Processes: 5
### Total private dirty RSS: 270.82 MB
.. 2 Passenger RackApp processes, OK.
But when I use the htop command, the output is as follows:
There seem to be a lot of Passenger Rackup processes. We're also running Sidekiq with the default configuration.
New Relic Server reports the following memory usage:
I tried tuning Passenger settings, adding a load balancer and another server but honestly don't know what to do from here. How can I find out what's causing so much memory usage?
Update: I had to restart ngnix because of some changes and it seemed to free quite a lot of memory.

Answer 1

Press Shift-H to hide threads in htop. Those aren't processes but threads within a process. The key column is RSS: you have two passenger processes at 209MB and 215MB and one Sidekiq process at 154MB.
Short answer: this is completely normal memory usage for a Rails app. 1GB is simply a little small if you want multiple processes for each. I'd cut down passenger to one process.

Answer 2

Does your application create child processes? If so, then it's likely that those extra "Passenger RackApp" processes are not actually processes created by Phusion Passenger, but are in fact processes created by your own app. You should double check whether your app spawns child processes and whether you clean up those child processes correctly. Also double check whether any libraries you use, also properly clean up their child processes.
I see that you're using Sidekiq and you've configured 25 Sidekiq processes. Those are also eating a lot of memory. A Sidekiq process eats just as much memory as a Passenger RackApp process, because both of them load your entire application (including Rails) in memory. Try reducing the number of Sidekiq processes.