I am building a basic chat application for customer support of a website. It works flawlessly in development on local server. I pushed the changes to the server but it is behaving extremely slow. The application in itself works fast but the pub/sub to acioncable channels is slow.
I am using nginx, puma for webserver and redis for pub/sub. I have four channels and two of them have heavy client side (coffee.erb file).How can I reduce time for actioncable channels? How can I debug what is causing the lag?
Thanking you in advance. If any code is required please mention in the comments of the question and I would add it to the question.
The most common cause for things running way more slowly on a server than locally is because they don't have nearly the same amount of RAM and start swapping. Just like an app being ridiculously slow on older phones.
In one case, the system swaps in and out memory, in the other case, the app swaps in and out resources itself (often implicitly through resource caches provided by the API).
The effect is the same: massive I/O overhead that doesn't exist on your development system / modern phone, leading to runtime behavior that is slower by several orders of magnitude.
I need to host a lot of simple rails/sinatra/padrino applications of different ruby versions each with 0..low hits per day. They belong to different owners and should be well isolated from each other.
When an app is hit it should respond in reasonably short time, but I expect several simultaneous visitors are hitting the same site to be a rare case.
I'm going to create separate os user for each application. Surely I'd like to put them as many per server as it's possible. Thus I need to choose the web server with the lowest memory footprint, which can run applications on behalf of different users with different ruby versions and gemsets.
I consider webrick,nginx+passenger,thin,apache+passenger. I suppose the reliability of all choices is sufficient for such a job, and while performance isn't an issue, the memory consumption is.
I found many posts regarding performance issues, but most of them discuss the performance tuning and issues. I couldn't find a comparison of web servers memory usage when idle.
Is "in process" webrick the best choice? Which one would you choose for that job?
And I couldn't figure out how to resolve subdomains to application ports with webrick. Shall I use nginx or apache for that?
I don't have much experience with hosting myself, but using Webrick for production is not a good idea I think. You can also check out mongrel which I saw used in production. In most cases though you will probably want to choose between thin and unicorn. Check out this http://cmelbye.github.com/2009/10/04/thin-vs-unicorn.html or google around. Good luck :-)
Why not use Heroku? Its free and gets you out of the hassle of server configuration and maintenance.
I have a Rails app that uses MySQL, MongoDB, NodeJS (and SocketIO). Right now, the app (everything) is hosted inside 1 box. I would like to know what I should do when the number of users grow. What factors should I take into account to determine whether I need to host a separate element in another box (like MySQL, Node, Mongo in each of its separate box). Should I just make that one single box bigger? Is there a best-practice method that I can go with?
If you guys can provide me with reference, guides, research regarding this topic. Please do. I am super noob at deployment and server configuration.
We faced this dilemma at work a short while ago and found that simply upgrading to a more powerful single box sufficed and would give us room to grow further by up to 3-4 times.
The most important thing would be to identify your potential bottlenecks.
In our case there were 2 bottlenecks. Disk I/O and the database's ability to utilise memory.
On our new server we had the hard drive array configured in such a way as to maximise the disk I/O and we upgraded the database software to allow it to use more memory. In fact the DBMS now keeps the entire database in memory and only performs write operations to the disk as needed. This significantly improved performance.
The short answer is move everything to its own box. The longer answer is: it depends on your app's usage.
I recommend you use Nagios or similar to monitor your app's resource utilization -- that is, how much CPU and RAM each of your services use. When one starts to each up too much resources (and your page load speed is negatively affected), move that to its own box.
Then continue to monitor that box, beef up when necessary or shard out.
The high scalability blog is good for reading on what other people have done.
i'm running a rails application with apache+passenger on virtual servers that do not have any swap space configured.
The site gets decent amount of traffic with 200K+ daily requests and sometimes the whole system runs out of memory causing odd behaviour on whole system.
The question is that is there any way to configure apache or passenger not to run out of memory (e.g. gracefully restarting passenger instances when they start using, say more than 300M of memory).
Servers have 4GB of memory and currently i'm using passenger's PassengerMaxRequests option but it does not seem to be the most solid solution here.
At the moment, i also cannot switch to nginx so that is not an option to preserve some room.
Any clever ideas i'm probably missing are welcome.
Edit: My temporary solution
I did not go with restarting Rails instances when they exceed certain amount of memory usage. Engine Yard wrote great blog post on the ActiveRecord memory bloat issue. This is our main suspect on the subject. As i did not have much time to optimize application, i set PassengerMaxRequests to 300 and added extra 2GB memory to server. Things have been good since then. At first i was worried that re-starting Rails instances continuously makes it slow but it does not seem to have impact i should worry about.
If you mean "limiting" as killing those processes and if this is the only application on the server and it is a Linux, then you have two choices:
Set maximum amount of memory one process can have:
# ulimit -m
unlimited
Or use cgroups for similar behavior:
http://en.wikipedia.org/wiki/Cgroups
I would advise against restarting instances (if that is possible) that go over the "memory limit", because that may put your system in infinite loops where a process repeatedly reaches that limit and restarts.
Maybe you could write a simple daemon that constantly watches the processes, and kills any that go over a certain amount of memory. Be sure to log any information about the process that did this so you can fix the issue whenever it comes up.
I'd also look into getting some real swap space on there... This seems like a bad hack.
I have a problem where passenger processes end up going out of control and consuming too much memory. I wrote the following script which has been helping to keep things under control until I find the real solution http://www.codeotaku.com/blog/2012-06/passenger-memory-check/index. It might be helpful.
Passenger web instances don't contain important state (generally speaking) so killing them isn't normally a process, and passenger will restart them as and when required.
I don't have a canned solution but you might want to use two commands that ship with Passenger to keep track of memory usage and nr of processes: passenger-status and sudo passenger-memory-stats, see
Passenger users guide for Nginx or
Passenger users guide for Apache.
I have a simple Rails app deployed on a 500 MB Slicehost VPN. I'm the only one who uses the app. When I run it on my laptop, it's fast enough. But the deployed version is insanely slow. It take 6 to 10 seconds to load the login screen.
I would like to find out why it's so slow. Is it my code? (Don't think so because it's much faster locally, but maybe.) Is it Slicehost's server being overloaded? Is it the Internet?
Can someone suggest a technique or set of steps I can take to help narrow down the cause of this problem?
Update:
Sorry forgot to mention. I'm running it under CentOS 5 using Phusion Passenger (AKA mod_rails or mod_rack).
If it is just slow on the first time you load it is probably because of passenger killing the process due to inactivity. I don't remember all the details but I do recall reading people who used cron jobs to keep at least one process alive to avoid this lag that can occur with passenger needed to reload the environment.
Edit: more details here
Specifically - pool idle time defaults to 2 minutes which means after two minutes of idling passenger would have to reload the environment to serve the next request.
First, find out if there's a particularly slow response from the server. Use Firefox and the Firebug plugin to see how long each component (including JavaScript and graphics) takes to download. Assuming the main page itself is what is taking all the time, you can start profiling the application. You'll need to find a good profiler, and as I don't actually work in Ruby on Rails, I can't suggest any: google "profile ruby on rails" for some options.
As YenTheFirst points out, the server software and config you're using may contribute to a slowdown, but A) slicehost doesn't choose that, you do, as Slicehost just provides very raw server "slices" that you can treat as dedicated machines. B) you're unlikely to see a script that runs instantly suddenly take 6 seconds just because it's running as CGI. Something else must be going on. Check how much RAM you're using: have you gone into swap? Is the login slow only the first time it's hit indicating some startup issue, or is it always that slow? Is static content served slow? That'd tend to mean some network issue (either on the Slicehost side, or your local network) is slowing things down, assuming you're not in swap.
When you say "fast enough" you're being vague: does the laptop version take 1 second to the Slicehost 6? That wouldn't be entirely surprising, if the laptop is decent: after all, the reason slices are cheap is because they're a fraction of a full server. You're using probably 1/32 of an 8 core machine at Slicehost, as opposed to both cores of a modern laptop. The Slicehost cores are quick, but your laptop could be a screamer compared to 1/4 of core. :)
Try to pint point where the slowness lies
1/ application is slow, or infrastructure (network + web server)
put a static file on your web server, and access it through your browser
2/ If it is fast, it is probable a problem with application + server configuration.
database access is slow
try a page with a simpel loop: is it slow?
3/ If it slow, it is probably your infrastructure. You can check:
bad network connection: do a packet capture (with Wireshark for example) and look for retransmissions, duplicate packets, etc.
DNS resolution is slow?
server is misconfigured?
etc.
What is Slicehost using to serve it?
Fast options are things like: Mongrel, or apache's mod_rails (also called passenger phusion or
something like that)
These are dedicated servers (or plugins to servers) which run an instance of your rails app.
If your host isn't using that, then it's probably defaulting to CGI. Rails comes with a simple CGI script that will serve the page, but it reloads the app for every page.
(edit: I suspect that this is the most likely case, that your app is running off of the CGI in /webapp_directory/public/dispatch.cgi, which would explain the slowness. This tends to be a default deployment on many hosts, since it doesn't require extra configuration on their part, but it doesn't give good performance)
If your host supports "Fast CGI", rails supports that too. Fast CGI will open a CGI session, and keep it open for multiple pages, so you get much better performance, but it's not nearly as good as Mongrel or mod_rails.
Secondly, is it in 'production' or 'development' mode? The easy way to tell is to go to a page in your app that gives an error. If it shows you a stack trace, it's in development mode, which is slower than production mode. Mongrel and mod_rails have startup options to determine whether to run the app in production or development mode.
Finally, if your database is slow for whatever reason, that will be a big bottleneck as well. If you do have a good deployment (Mongrel/mod_rails/etc.) in production mode, try looking into that.
Do you have a lot of data in your DB? I would double check that you have indexed all the appropriate columns- because this can make a huge difference. On your local dev system, you probably have a lot more memory than on your 500 mb slice, which would result in the DB running a lot slower if you have big, un indexed tables. You can also run the slow queries logger in MySql to pinpoint columns without indexes.
Other than that, yes- passenger will need to spool up a process for you if you have not been using the site recently. If this is the case, you should see a significant speed increase on second, and especially third and later page loads.
You might want to run a local virtual machine with 500 MB. Are you doing a lot of client-server interaction? Delays over the WAN are significant
You might want to check out RPM (there's a free "lite" version too) and/or New Relic's Tune Up.
Your CPU time is guaranteed by Slicehost using the Xen virtualization system, so it's not that. Don't have the other answers for you, sorry! Might try 'top' on a console while you're trying to access the page.
If you are using FireFox and doing localhost testing (or maybe even on LAN) you may want to try editing the network.dns.disableIPv6 setting.
Type about:config in the address bar and filter for network.dns.disableIPv6 and double-click to set to true.
This bug has been reported mainly from Vista OS's, but some others as well.
You could try running 'top' when you SSH in to see which process is heavy. If you also have problems logging you, perhaps you may try getting Statistics in the Slicehost manager.
If you discover it is MySQL's fault, consider decreasing the number of servers it can spawn.
512 seems decent for Rails application, you might have to check if you misconfigured too.