Every n seconds application is requesting a remote JSON file that provides live prices for securities in the Trading system. JSON has a block with the data I need (marketdata) and a block with the current dataversion(version and seqnum).
Right now I use ActionController::Live (with EventSource on the client side) to push updated data to the browser. All actions are done within one method:
opening SSE connection;
forming dynamic URL;
pulling new data from remote server;
comparing/reassigning seqnum value;
updating database if needed.
So my goal now is to separate pulling & updating the database (ActiveJob) with pushing updated values to the browser (ActionController::Live). To accomplish this I need:
either to store somewhere on the server side seqnum & version to share between controller and background job;
or monitor databases for the latest changes in the updated_at fields.
So basically I have two questions:
What is more efficient between the two options above?Are there any other good approaches?
(in case the first one has a right to exist) How to implement this approach?
Considering the fact that you might have, for example, multiple rails process running, I believe it becomes quite hard for you to let activejob talk directly to rails controller in some way.
Defintely store seqnum and version, I wouldn't rely on updated_at in any case, it's too easy to get it updated randomly and so end up sending stuff to the client without any real reason. Also in this case they seem like very solid fields to point out if the file has been updated.
With polling
That being said, you want to "signal" ActionController::Live in some way and I'm afraid polling here is your only option, unless on your client side there is a specific moment when it needs to know if the file has been updated, in which case you might want to use websockets or something similar.
So, something like
cached_request = YourCachedRequest.latest # Assuming it returns a single record
updated = true
loop do
if updated
updated = false
response.stream.write cached_request.serialize_in_some_way
end
current_version = cached_request.version # use seqnum too if you need
cached_request = cached_request.reload
updated = true if cached_request.version > current_version
sleep 20.0
end
Without polling
If you want an option that doesn't involve polling, you can only go for websockets I believe. However you have a more efficient option:
Create a mini application (evenmachine/sinatra/something light) where the clients will poll (you can pass through your main application to distribute this to differente nodes of this mini application), the point of this app is only to reroute messages from your main application to polling clients.
Now, you can create an internal API endpoint for your main application that it's used only by delayed job. Delayed job will hit this endpoint only when it notices that the fetched JSON is actually updated relative to the one currently stored. If that's the case, it will hit your main app API endpoint which in turn will send a message (again, probably through an HTTP API endpoint, this time on your mini app) to all your mini app instances, which in turn will send them to your clients.
In this way, you don't overload your main server but only these mini-nodes which can have localized outages (which is a big advantage, instead of having a big system outage).
Related
I am working in a Rails application and below is the scenario requiring a solution.
I'm doing some time consuming processes in the background using Sidekiq and saves the related information in the database. Now when each of the process gets completed, we would like to show notifications in a separate area saying that the process has been completed.
So, the notifications area really need to pull things from the back-end (This notification area will be available in every page) and show it dynamically. So, I thought Ajax must be an option. But, I don't know how to trigger it for a particular area only. Or is there any other option by which Client can fetch dynamic content from the server efficiently without creating much traffic.
I know it would be a broad topic to say about. But any relevant info would be greatly appreciated. Thanks :)
You're looking at a perpetual connection (either using SSE's or Websockets), something Rails has started to look at with ActionController::Live
Live
You're looking for "live" connectivity:
"Live" functionality works by keeping a connection open
between your app and the server. Rails is an HTTP request-based
framework, meaning it only sends responses to requests. The way to
send live data is to keep the response open (using a perpetual connection), which allows you to send updated data to your page on its
own timescale
The way to do this is to use a front-end method to keep the connection "live", and a back-end stack to serve the updates. The front-end will need either SSE's or a websocket, which you'll connect with use of JS
The SEE's and websockets basically give you access to the server out of the scope of "normal" requests (they use text/event-stream content / mime type)
Recommendation
We use a service called pusher
This basically creates a third-party websocket service, to which you can push updates. Once the service receives the updates, it will send it to any channels which are connected to it. You can split the channels it broadcasts to using the pub/sub pattern
I'd recommend using this service directly (they have a Rails gem) (I'm not affiliated with them), as well as providing a super simple API
Other than that, you should look at the ActionController::Live functionality of Rails
The answer suggested in the comment by #h0lyalg0rithm is an option to go.
However, primitive options are.
Use setinterval in javascript to perform a task every x seconds. Say polling.
Use jQuery or native ajax to poll for information to a controller/action via route and have the controller push data as JSON.
Use document.getElementById or jQuery to update data on the page.
I have a rails app that people can send data to in the query params of a url. The rails app then validates the correctness of the data and creates a json reponse listing any detected errors. The validation itself is done by checking the data against a set of rules that live in a github repo.
Ideally I'd like to update my local copy of this repo once a day. In order to prevent complications I'd like any requests that come in while this update takes place to back off for a few seconds.
What's the best way to communicate to the incoming requests that an update is currently occuring? I'm using a process based webserver (unicorn), so memory mutexes don't seen like the right answer :(.
I am designing a Rails app that takes in requests, uses data within the request to call a 3rd party web service, process the reply and then sends out a response to the original requestor and also issues a PUT request to yet another service.
I am trying to wrap my head around how to design this Rails app as it's different from the canonical Rails structure.
The objects are Lists and Tasks. Each List has many Tasks, and each Task belongs to a List.
The request I would get is something like:
http://myrailsapp.heroku.com/v1/lists?id=1&from=2012-02-12&to=2012-02-14&priority=high
In this example I am requesting tasks from 2/12/2012 to 2/14/2012 with a high priority in List #1
I would then issue a 3rd party web service call like this:
http://thirdpartywebservice.com/v1/lists?id=4128&from=2012-02-12&to=2012-02-14&priority=high
As you can see some processing was done on the data (id was changed in this case)
The results are then sent back to the requestor and to another web service via PUT.
My question is, how do I set up the Rails app to handle these types of behaviors? How does the controller structure change? This looks like a good use case for queues, how do I distribute multiple concurrent requests among queues?
For one thing I don't need data persistence (data can be discarded after the response is sent out) and also data structure design is simplified. (I don't think I need ruby objects, simply dictionaries or hashes representing these would be lighter weight and quicker to implement)
Edit
So I broke down the work flow of the app into these components
Parse incoming request
Construct 3rd part web service request
Send 3rd party request
Enqueue a worker to process the expected response
Process the response once it arrives
Send the parsed result back as a response
Which of the standard ruby controllers handle each of these steps? What are the models needed besides Lists and Tasks?
You should still use a database because passing data to Resque is messy. Rather, you should store it in the database and then pass the id to the workers, fetch the data, commit any new data or delete the record. It's really up to you but this method is cleaner. You can also use a push service like faye to let the user know when the processing is complete.
If you expect to have many concurrent requests, I would recommend Sidekiq as it's less of a memory hog. Having 4-5 resque workers can already suck up about 512 MB. The controller structure should not change. Please comment on anything you need clarified and I'll be happy to update my answer.
EDIT
You would want to use a separate database store, such as Postgres. Not sure if it's important what models you need, but essentially this is what should be happening.
In your controller, create a Request object which contains the query params you want to query this 3rd party service with. Then enqueue a job to be handled by Sidekiq/Resque, let's call this ThirdPartyRequest and pass in the id of the Request object you just created as an argument. Then render a view here showing the Request object. Let's say that Request#response is still empty cause it hasn't been processed yet, so let the user know it's still processing.
A worker then handles your job ThirdPartyRequest. ThirdPartyRequest should then fetch the Request object and obtain the query params needed to contact the third party service. It does that then gets a Request. Update the Request object with this Request then save it.
class ThirdPartyRequest
def self.perform(request_id)
request = Request.find(request_id)
# contact third party service
request.response = ...
request.save
end
end
The user can continually refresh his page to check on his/her Request object. Once it gets updated with the response, they will know its completed. If you want the page to refresh automatically, look into faye/juggernaut/private_pub or a SaaS solution like Pusher.
I am building an application which will send status requests to users (via email & sms) on a regular basis. I want to execute the service each hour which will:
Query the database for all requests that need to be sent (based on some logic)
Send the requests through Amazon's Simple Email Service (this is already working)
Write a record of the status request notification back to the data store
I am considering wrapping up this series of operations into a single controller with an end point that can be called remotely to kick off the process within the rails app.
Longer term, I will break this process out into an app that can be run independently of my rails app, but for now I'm just trying to keep it simple.
My first inclination is to build the following:
Controller with the following elements:
A method which will orchestrate the steps outlined above (and can be called externally)
A call to the status_request model which will bring back a collection of request needing to be sent
A loop to iterate through the pending requests, which will:
Make a call to my AWS Simple Email Service module to actually send the email, and
Make a call to the status_request model to log the request back to the database
Model:
A method on my status_request model which will bring back a collection of requests that need to be sent
A method in my status_request model which will log that a notification was sent
Since this will behave as a service that gets called periodically from an outside scheduler I don't think I'll need a view for this operation. (Will, of course, need views to show users and admins what requests have been sent, but that's later...).
As someone new to Rails, I'm asking for review of this approach and any suggestions you may have.
Thanks!
Instead of a controller which Jeff pointed out exposes a security risk, you may just want to expose a rake task and use cron to invoke it on an hourly basis.
If you are still interested in building a controller, look at devise gem and its single access token, token_authenticatable, for securing the methods you are exposing.
You may also want to look at delayed_job or resque to offload the call to status_request and the loop to AWS simple service to a background worker process.
You may want a seperate controller and view for the log file so you can review progress on demand.
And if you want to get real fancy use Amazon SNS to send you alerts when the service reaches some unacceptable level of failures, backlog, etc.
Since you are trying to invoke this from an outside process, your approach should work. You could also have a worker process that processes task when they are there.
You will need routes to expose your service, and you may want to also make security decisions. How will the service that invokes your application authenticate so all others can't hit it at will?
Another consideration should be how many emails are you sending. If there are enough, we may want to look into the fact that writing this sort of loop is going to be extremely top heavy; and may affect users on the current system if it's a web application.
In the end, there are many ways to do this. I would focus on the performance/usage you expect as well as security. There's never one perfect way to solve a problem like this, and your way should just be aware of the variables it will need to be operating within.
Resque and Redis might be helpful to you in scheduling and performing operatio n .They are simple and superfast, [here](http://railscasts.com/episodes/271-resque] is a simple tut on same.
I am to build a web application which will accept different events from external sources and present them quickly to the user for further actions. I want to use Ruby on Rails for the web application. This project is a internal development project. I would prefer simple and easy to use solutions for rapid development over high reliable and complex systems.
What it should do
The user has the web application opened in his browser. Now an phone call comes is. The phone call is registered by a PBX monitoring daemon. In this case via the Asterisk Manager Interface. The daemon sends the available information (remote extension, local extension, call direction, channel status, start time, end time) somehow to the web application. Next the user receives a notified about the phone call event. The user now can work with this. For example by entering a summary or by matching the call to a customer profile.
The duration from the first event on the PBX (e.g. the creation of a new channel) to the popup notification in the browser should be short. Given a fast network I would like to be within two seconds. The single pieces of information about an event are created asynchronously. The local extension may be supplied separate from the remote extension. The user can enter a summary before the call has ended. The end time, new status etc. will show up on the interface as soon as one party has hung up.
The PBX monitor is just one data source. There will be more monitors like email or a request via a web form. The monitoring daemons will not necessarily run on the same host as the database or web server. I do not image the application will serve thousands of logged in users or concurrent requests soon. But from the design 200 users with maybe about the same number of events per minute should not be a scalability issue.
How should I do?
I am interested to know how you would design such an application. What technologies would you suggest? How do the daemons communicate their information? When and by whom is the data about an event stored into the main database? How does the user get notified? Should the browser receive a complete dataset on behalf of a daemon or just a short note that new data is available? Which JS library to use and how to create the necessary code on the server side?
On my research I came across a lot of possibilities: Message brokers, queue services, some rails background task solutions, HTTP Push services, XMPP and so on. Some products I am going to look into: ActiveMQ, Starling and Workling, Juggernaut and Bosh.
Maybe I am aiming too hight? If there is a simpler or easier way, like just using the XML or JSON interface of Rails, I would like to read this even more.
I hope the text is not too long :)
Thanks.
If you want to skip Java and Flash, perhaps it makes sense to use a technology in the Comet family to do the push from the server to the browser?
http://en.wikipedia.org/wiki/Comet_%28programming%29
For the sake of simplicity, for notifications from daemons to the Web browser, I'd leave Rails in the middle, create a RESTful interface to that Rails application, and have all of the daemons report to it. Then in your daemons you can do something as simple as use curl or libcurl to post the notifications. The Rails app would then be responsible for collecting the incoming notifications from the various sources and reporting them to the browser, either via JavaScript using a Comet solution or via some kind of fatter client implemented using Flash or Java.
You could approach this a number of ways but my only comment would be: Push, don't pull. For low latency it's not only quicker it's more efficient, as your server now doesn't have to handle n*clients once a second polling the db/queue. ActiveMQ is OK, but Starling will probably serve you better if you're not looking for insane levels of persistence.
You'll almost certainly end up using Flash on the client side (Juggernaut uses it last time I checked) or Java. This may be an issue for your clients (if they don't have Flash/Java installed) but for most people it's not an issue; still, a fallback mechanism onto a pull notification system might be prudent to implement.
Perhaps http://goldfishserver.com might be of some use to you. It provides a simple API to allow push notifications to your web pages. In short, when your data updates, send it (some payload data) to the Goldfish servers and your client browsers will be notified, with the same data.
Disclaimer: I am a developer working on goldfish.
The problem
There is an event - either external (or perhaps internally within your app).
Users should be notified.
One solution
I am myself facing this problem. I haven't solved it yet, but this is how I intend to do it. It may help you too:
(A) The app must learn about the event (via an exposed end point)
Expose an end point by which you app can be notified about external events.
When the end point is hit (and after authentication then users need to be notified).
(B) Notification
You can notify the user directly by changing the DOM on the current web page they are on.
You can notify users by using the Push API (but you need to make sure your browsers can target that).
All of these notification features should be able to be handled via Action Cable: (i) either by updating the DOM to notify you when a phone call comes in, or (ii) via a push notification that pops up in your browser.
Summary: use Action Cable.
(Also: why use an external service like Pusher, when you have ActionCable at your disposal? Some people say scalability, and infrastructure management. But I do not know enough to comment on these issues. )