I have two asp.net applications, one of which is a publisher of data, one is a subscriber. It's possible there will be more subscribers too. The list is not anonymous, I know my applications.
What would be the best strategy to notify the subscribers when there is data in the publisher?
There are several message brokers and queueing systems on the internet, most are hard to implement and require code that I don't really find desirable (for instance running a service on the machines of the applications, where the services do the communication).
I don't mind running a server somehow that brokers messages, like a hub, but I would prefer a hub that offers an HTTP API I can call from my publisher, and that calls an HTTP page on the subscribers (kind of like PubSubHubbub but that appears to be very much about RSS feeds).
It's a bit unfeasable to write my own queueing system because there are some hard problems in that as well. Also calling the list of subscribers from publisher directly will cause some performance issues that I also want to avoid.
Do you know of solutions I can try?
PS: if this message is better suited for Programmers#StackExchange, feel free to move it!
Related
I need to create a web UI for a client company to allow them to monitor which subscribers (Microservices) are up and if they are part of a worker queue, how many of them are running.
Although this is easy to implement by keeping sending a signal to another instance of NATS (to minimize overheads) for monitoring, I would like to ask if there is any built-in feature that can provide this functionality.
This link suggests that there is a monitoring endpoint built-in but I am not sure if I can get what I need out of it. So do I have to start inventing the wheel, or is there something that can be used out of the box?
I am building a microservice application, and I try to follow the best practices. I use event sourcing and event driven state transfer in many places, but I realized that sometimes I just need to call another service in an asynchronous way to kindly ask it to do something e.g. send out a registration email (as the email service is a technical component and not a domain). I noticed that many times, services just call the other's service API endpoint, but that wouldn't be asynchronous. As I don't expect any returned value when calling from another service, the command would only produce events, RPC is not necessary.
In the end, my plan is to implement commands/actions that can be triggered by clients from REST API (then the commands may also produce responses) or by events or other services from RabbitMQ or similar. This leads me to how should I define the data structure of the command/action, is there any specification for that? Or existing solutions for Python? Or should I do something differently?
I'm designing a database monitoring application. Basically, the database will be hosted in the cloud and record-level access to it will be provided via custom written clients for Windows, iOS, Android etc. The basic scenario can be implemented via web services (ASP.NET WebAPI). For example, the client will make a GET request to the web service to fetch an entry. However, one of the requirements is that the client should automatically refresh UI, in case another user (using a different instance of the client) updates the same record AND the auto-refresh needs to happen under a second of record being updated - so that info is always up-to-date.
Polling could be an option but the active clients could number in hundreds of thousands, so I'm looking for a more robust and lightweight (on server) solution. I'm versed in .NET and C++/Windows and I could roll-out a complete solution in C++/Windows using IO Completion Ports but feel like that would be an overkill and require too much development time. Looked into ASP.NET WebAPI but not being able to send out notifications is its limitation. Are there any frameworks/technologies in Windows ecosystem that can address this scenario and scale easily as well? Any good options outside windows ecosystem e.g. node.js?
You did not specify a database that can be used so if you are able to use MSSQL Server, you may want to lookup SQL Dependency feature. IF configured and used correctly, you will be notified if there are any changes in the database.
Pair this with SignalR or any real-time front-end framework of your choice and you'll have real-time updates as you described.
One catch though is that SQL Dependency only tells you that something changed. Whatever it was, you are responsible to track which record it is. That adds an extra layer of difficulty but is much better than polling.
You may want to search through the sqldependency tag here at SO to go from here to where you want your app to be.
My first thought was to have webservice call that "stays alive" or the html5 protocol called WebSockets. You can maintain lots of connections but hundreds of thousands seems too large. Therefore the webservice needs to have a way to contact the clients with stateless connections. So build a webservice in the client that the webservices server can communicate with. This may be an issue due to firewall issues.
If firewalls are not an issue then you may not need a webservice in the client. You can instead implement a server socket on the client.
For mobile clients, if implementing a server socket is not a possibility then use push notifications. Perhaps look at https://stackoverflow.com/a/6676586/4350148 for a similar issue.
Finally you may want to consider a content delivery network.
One last point is that hopefully you don't need to contact all 100000 users within 1 second. I am assuming that with so many users you have quite a few servers.
Take a look at Maximum concurrent Socket.IO connections regarding the max number of open websocket connections;
Also consider whether your estimate of on the order of 100000 of simultaneous users is accurate.
Best I could find was this wiki entry
I I thought "surely there must be more to it than this".
Am I missing something?
From the doc:
What is WebHook?
The concept of a WebHook is simple. A WebHook is an HTTP callback: an
HTTP POST that occurs when something happens; a simple event-notification via HTTP POST.
A web application implementing WebHooks will POST a message to a URL
when certain things happen. When a web application enables users to
register their own URLs, the users can then extend, customize, and
integrate that application with their own custom extensions or even
with other applications around the web. For the user, WebHooks are a
way to receive valuable information when it happens, rather than
continually polling for that data and receiving nothing valuable most
of the time. WebHooks have enormous potential and are limited only by
your imagination! (No, it can't wash the dishes. Yet.)
Why should I care?
As integrated as we perceive the web, most web applications today
operate in silos. With the rise of API's we've seen mashups and some
degree of integration between applications. However, we have not seen
the vision of the programmable web: a web where you as the user can
"pipe" data between apps much like the Unix command line. Some say RSS
is the answer. They are wrong. The heart is in the right place, but
the implementation is wrong. RSS is still useful, but it is not going
to bring us the true programmable web.
We just need a simple way to get data out in real-time to let the user easily do whatever >they wantwith it. That means no polling, no content constraints, and no XML
parsing. That means no RSS. Using HTTP is simpler and easier to use.
PHP is a very popular and accessible programming environment, so it's
likely to be used often for writing hooklets... getting data from a
web POST in PHP is as simple as $_POST['something']. And making the
request to the user script is as simple as making an HTTP request,
something already built-in to most programming environments. In fact,
web hooks are easier to implement than an API.
I have been given access to a real time data feed which provides location information, and I would like to build a website around this, but I am a little unsure on what architecture to use to achieve my needs.
Unfortunately the feed I have access to will only allow a single connection per IP address, therefore building a website that talks directly to the feed is out - as each user would generate a new request, which would be rejected. It would also be desirable to perform some pre-processing on the data, so I guess I will need some kind of back end which retrieves the data, processes it, then makes it available to a website.
From a front end connection perspective, web services sounds like it may work, but would this also create multiple connections to the feed for each user? I would also like the back end connection to be persistent, so that data is retrieved and processed even when the site is not being visited, I believe IIS will recycle web services and websites when they are idle?
I would like to keep the design fairly flexible - in future I will be adding some mobile clients, so the API needs to support remote connections.
The simple solution would have been to log all the processed data to a database, which could then be picked up by the website, but this loses the real-time aspect of the data. Ideally I would be looking to push the data to the website every time the data changes or now data is received.
What is the best way of achieving this, and what technologies are there out there that may assist here? Comet architecture sounds close to what I need, but that would require building a back end that can handle multiple web based queries at once, which seems like quite a task.
Ideally I would be looking for a C# / ASP.NET based solution with Javascript client side, although I guess this question is more based on architecture and concepts than technological implementations of these.
Thanks in advance for all advice!
Realtime Data Consumer
The simplest solution would seem to be having one component that is dedicated to reading the realtime feed. It could then publish the received data on to a queue (or multiple queues) for consumption by other components within your architecture.
This component (A) would be a standalone process, maybe a service.
Queue consumers
The queue(s) can be read by:
a component (B) dedicated to persisting data for future retrieval or querying. If the amount of data is large you could add more components that read from the persistence queue.
a component (C) that publishes the data directly to any connected subscribers. It could also do some processing, but if you are looking at doing large amounts of processing you may need multiple components that perform this task.
Realtime web technology components (D)
If you are using a .NET stack then it seems like SignalR is getting the most traction. You could also look at XSockets (there are more options in my realtime web tech guide. Just search for '.NET'.
You'll want to use signalR to manage subscriptions and then to publish messages to registered client (PubSub - this SO post seems relevant, maybe you can ask for a bit more info).
You could also look at offloading the PubSub component to a hosted service such as Pusher, who I work for. This will handle managing subscriptions and component C would just need to publish data to an appropriate channel. There are other options all listed in the realtime web tech guide.
All these components come with a JavaScript library.
Summary
Components:
A - .NET service - that publishes info to queue(s)
Queues - MSMQ, NServiceBus etc.
B - Could also be a simple .NET service that reads a queue.
C - this really depends on D since some realtime web technologies will be able to directly integrate. But it could also just be a simple .NET service that reads a queue.
D - Realtime web technology that offers a simple way of routing information to subscribers (PubSub).
If you provide any more info I'll update my answer.
A good solution to this would be something like http://rubyeventmachine.com/ or http://nodejs.org/ . It's not asp.net, but it can easily solve the issue of distributing real time data to other users. Since user connections, subscriptions and broadcasting to channels are built in to each, that will make coding the rest super simple. Your clients would just connect over standard tcp.
If you needed clients to poll for updates then you would need a que system to store info for the next request. That could be a simple array, or a more complicated que system depending on your requirements and number of users.
There may be solutions for .net that I am not aware of that do the same thing, but those are the 2 I know of.