I am a newbie to rails. I have used feature flags when i was in java world. I found that there are a few gems in rails (rollout and others) for doing it. But how to turn a feature on/off on the fly in rails.
In java we can use a mbean to turn features on the fly. Any idea or pointers on how to do this? I dont want to do a server restart on my machines once a code is deployed.
Unless you have a way of communicating to all your processes at once, which is non-standard, then you'd need some kind of centralized configuration system. Redis is a really fast key-value store which works well for this, but a database can also do the job if a few milliseconds per page load to figure out which features to enable isn't a big deal.
If you're only deploying on a single server, you could also use a static YAML or JSON configuration file that's read before each request is processed. The overhead of this is almost immeasurable.
Related
Are there any recommended Load Test tools / services that are able to cycle through AWS Application Load Balancer logs stored in S3 preferably utilising the time stamps to perform piano roll type functionality?
aws-log-replay seems to be something you're looking for, it can replay requests with defined concurrency.
With regards to more or less popular load testing tools I can only think of Apache JMeter with Access Log Sampler which support out of box access log files from Tomcat, Weblogic, Reisin and SunOne, however you can come up with your own implementation of Generator class or dynamically populate HTTP Request sampler fields using JSR223 PreProcessor like it's described in Stop Making Assumptions! Learn How to Replay Your Production Traffic With JMeter guide.
Actually I don't think you will be able to produce realistic load by replaying your access logs, it might work for something simple like static content, however if your application assumes authentication, sessions, complex workflows, etc. - I'm afraid your "replay" attempt will got stuck at login page.
So instead of trying to replay complex scenarios from the logs I would suggest sticking to the load testing tool of your choice and create it from scratch. Access logs can be used to identify workload distribution (like X % of users are normally doing this, Y % are doing that, etc.) and anticipated concurrency (like at X time we had Y online users).
I'm studying the best way to have multiple redmine instances in the same server (basically I need a database for each redmine group).
Until now I have 2 options:
Deploy a redmine instance for each group
Deploy one redmine instance with multiple database
I really don't know what is the best practice in this situation, I've seen some people doing this in both ways.
I've tested the deployment of multiple redmines (3 instances) with nginx and passenger. It worked well but I think with a lot of instances it may not be feasible. Each app needs around 100mb of RAM, and with the increasing of requests it tends to allocate more processes to the app. This scenario seems bad if we had a lot of instances.
The option 2 seems reasonable, I think I can implement that with rails environments. But I think that there are some security problems related with sessions (I think a user of site A is allowed to make actions on site B after an authentication in A).
There are any good practice for this situation? What's the best practice to take in this situation?
Other requirement related with this is: we must be able to create or shut down a redmine instance without interrupt the others (e.g. we should avoid server restarts..).
Thanks for any advice and sorry for my english!
Edit:
My solution:
I used a redmine instance for each group. I used nginx+unicorn to manage each instance independently (because passenger didn't allow me to manage each instance independently).
The two options are not so different after all. The only difference is that in option 2, you only have one copy of the code on your disk.
In any case, you still need to run different worker processes for each instance, as Redmine (and generally most Rails apps) doesn't support database switching for each request and some data regarding a certain environment are cached in process.
Given that, there is not really much incentive to share even the codebase as it would require certain monkey patches and symlink-magic to allow the proper initialization for the intentional configuration differences (database and email configuration, paths to uploaded files, ...). The Debian package does that but it's (in my eyes) rather brittle and leads to a rather non-standard system.
But to stress again: even if you share the same code on the disk between instances, you can't share the running worker processes.
Running multiple instances from the same codebase is not officially supported by Redmine. However, Debian/Ubuntu packages seem to support such approach... See:
Multiple instances of redmine on Debian squeeze
So, generally:
If you use Debian/Ubuntu go with option #2
Otherwise go with #1
Rolling forward a couple of years, and you might now want to consider a third option of using docker containers for each of your redmine instances.
I've been using https://github.com/sameersbn/docker-redmine.git , and have been quite happy with it except that it doesn't yet support handling of incoming mail for creating and commenting on tickets.
I am working on a rails application that requires files to be uploaded to my server and then have resque workers (running on several other computers) use those files to do some tasks. I have my workers all set to do the task but I can't seem to find a nice way to get the files from my host computer to my worker computers. I've tried Carrierwave (and looked the documentation for Paperclip), but all I see is using S3 which I cannot use. My only idea is to store a string which contains the URI where the file may be found so that the workers can download them and start working. I'm not particularly fond this idea. Does anyone have any suggestions on what might be best way to do this? Thank you!
Update
I should also note the files that need to be shared are roughly 200MB each
Have you considered something like a Network File System instead of doing this inside your application?
Depending on what platform your workers and server are you should have numerous options to share a filesystem (I assume you have a LAN running between them).
And even if no real LAN, sshfs could work too..
The upsides are obvious: Your Ruby application only has to deal with a regular filesystem using FileUtils and the heavy lifting of pushing stuff around is handled by a much more reliable infrastructure
In the question What little things do I need to do before deploying a rails application I am getting a lot of answers that are bigger than "little things". So this question is slighly different.
What reasonably major steps do I need to take before deploying a rails application. In this case, i mean things which are are going to take more than 5 mins, and so need to be scheduled. For small oneline config changes, please use the little things question.
Set up Capistrano to deploy You'll want to learn capistrano if you don't already know it, and use it to deploy your code in an automated way. This will involve setting up your shared directory and shared resources like database.yml.
Install C Based MySQL gem If you don't have all the required libs, this can take a little while, but less than 20 minutes.
Make sure you aren't vulnerable to common web application attacks Session fixation, session hijacking, cross-site scripting, SQL injection (probably you don't have to worry much about SQL injection). Be sure you use h() when outputting user-entered data in a view screen. Lots of good material online about this.
Choose a server architecture Nginx, Mongrel, FastCGI, CGI, Apache, Passenger: there is a lot to choose from. Think about how your app will be used and decide on the best architecture, then set it up.
Set up Exception Notifier or Exception Logger You will want your app to warn you when it breaks. Set one of these tools up to track production exceptions. Note: Exception notifier will warn you when routing errors occur (i.e. when people fat-finger URLs or script kiddies attack you): so think about what you want the framework to do when that happens and adjust accordingly.
Make sure all of your passwords are out of source control If you have database.yml, mail.yml (if you use yaml_mail_config) or other sensitive files in source control, get them out of there, replace them with database.yml.example, and put them in the shared/ folder on your server.
Ensure that your DB is locked down. A lot of people forget to secure MySQL when setting up their new production Rails box. Don't be like them.
Make sure all of the little web-files are in place If you are planning to be listed in Google, generate a sitemap.xml file. If you are planning to use an .htaccess file for something, make sure it's there. If you need a robots.txt file to prevent certain areas of your site from being indexed, make one. If you want a good looking 404 Page, make sure it's set up correctly. If you want a "Be Right Back" page to be present when you deploy, make sure that you have a Capistrano maintenance file specified and Nginx or Apache knows how and when to redirect to it.
Get your SSL Certs in place If you are going to use SSL, make sure you get certificates that are valid on your production domain, and set them up.
Use some process monitoring
Sometimes your processes (mongrels in many cases) will die or other bad things will happen to them. For example a memory leak could cause the memory consumption to increase indefinitely or a process could start using all your CPU.
monit and god are both good choices to save you from this fate. They can also be set to hit a url on your site to check for a 200 response code.
Set up server monitoring
Some suggestions in this space: fiveruns, newrelic, scout
These tools will record detailed metrics on your servers and are invaluable when something goes wrong and you need to see what actually happened. They also give you real time information on server load.
If you have a cluster this kind of reporting is even more critical.
Backup
Write a script to periodically backup your database and any other assets that your users can upload. S3 might be a good choice for this.
Choose a web server / load balancer
My preferred server is nginx, but the common pattern is to start with apache + mod_proxy_http.
We all hear a lot about scaling issues in Rails.
I was just curious what the actual costs in handling a HTTP request is in the Rails framework. Meaning, what has to happen for each and every request which comes in? Is there class parsing? Configuration? Database Connection establishment?
That actually depends a lot on which web server you're using, and which configuration you're using, not to mention the application design itself. Configuration and design issues involved include:
Whether you're using fastcgi, old-school cgi, or some other request handling mechanism (affects whether you're going to have to rerun all of the app initialization code per request or not)
Whether you're using memcache (or an alternate caching strategy) or not (affects cost of database requests)
Whether you're using additional load balancing techniques or not
Which session persistence strategy you're using (if needed)
Whether you're using "development" mode or not, which causes code files to be reloaded whenever they're changed (as I recall; maybe it's just per-request) or not
Like most web app frameworks, there are solutions for connection pooling, caching, and process management. There are a whole bunch of ways to manage database access; the usual, default ones are not necessarily the highest performance, but it's not rocket science to adjust that strategy.
Someone who has dug into the internals more deeply can probably speak in more excruciating detail, but most apps use either FastCGI on Apache or an alternate more rails-friendly web server, which means that you only have app setup once per process.
Until the release of Phusion Passenger (aka mod_rails) the "standard" for deployment was not FastCGI but using a cluster of Mongrel servers fronted by Apache and mod_proxy (or Nginx etc).
The main issue behind the "Rails doesn't scale" is the fact that there are some quite complicated threading issues which has meant tiwht the current version of Ruby and the available serving mechanisms, Rails has not been threadsafe. This has meant that multiple containers have been required to run a Rails app to support high-levels of concurrent requests. Passenger makes some of this moot, as it handles all of this internally, and can also be run on a custom build of Ruby (Ruby Enterprise Edition) that changes the way memory is handled.
On top of this, the upcoming versions of both Ruby and Rails are directly addressing the threading issue and should close this argument once and for all.
As far as I am concerned the whole claim is pretty bogus. "Scale" is an architectural concern.
Here's a good high level overview of the lifecycle of a Rails request. After going through this, you can choose specific sections to profile and optimize.