As for clarification, this question is not duplicated since the
situation differs from other related questions.
We are working on an client side application which will receive data from a server side PHP-powered web application. Data are critical and must be delivered to user as soon as possible. It doesn't matter if client request for data from server or server push data to client, the only thing we need is a reliable and fast option.
There are several methods but non of them fit our project:
Use GCM push notification ability:
This is a great option but in practice, we lost several pushes so it's not reliable and in other hand, delay is so much. I repeat, the situation is critical so it must be fast.
Request data from server by the client with a 1 or 2 second interval:
This is what we think is the best solution so far but is really expensive. It's reliable and fast. But in other hand, the pressure on our disturbed servers get extremely high and they become useless even with our current client numbers. If the number of clients get larger, we'll be down.
SMS based push:
The other option for us is to send SMS to client phones and use that data to operate application. Using this method, the pressure on our server will get really low (just like GCM option). But sending SMS in our countries mobile network is usually delayed, normally, 10 seconds. Although this option have good reliability but the speed so low that we can't use it.
FM radio signal based push:
We can use clients FM radio receiver to get data from local broadcasting stations. This method is reliable and very fast but the cost of stations will kill us! and even if we handle it (read: we can't), clients does not connect their earphone to the smartphones always.
So, what are the alternatives? what is a reliable and almost fast method which does not make a lot of pressure on our servers?
Would probably recommend using WebSockets for case you describe (using OkHttp library for example) - see following for nice overview of it's use https://medium.com/#ssaurel/learn-to-use-websockets-on-android-with-okhttp-ba5f00aea988. A common pattern would be use of WebSockets with Http REST requests (for an initial catch up query for example). Also you would typically only use WebSockets while app was in foreground and rely on push notifications otherwise.
Let's say have an app that has 10s of millions of installs and 10s of thousands of active users at a given point of time. I need to log my users' activity data to my servers. Currently, I make HTTP requests from the device to my servers. I have a bunch of machines running a web server, sitting behind amazon's ELB. They parse the data coming from the devices and put it in mongodb.
Now, I would like to capture device data by using upstream CCS provided by Google' GCM (so that I can piggyback on GCM for more reliable delivery of data) I have written a prototype XMPP server and I can make whole thing work, but I am worried about scaling it up. What will happen if Google starts sending me messages at a rate faster than I can consume? Earlier, I was able to use multiple servers behind load balancer to tackle high request rate. Is there a concept of load balancing here?
If I open multiple connections from my server to Google's server (Google says I can have till 1000 connections for a given sender id), will the incoming requests be load balanced between these connections?
Finally, is there recommended solution which takes care of solving most of the problems above? Will using ejabberd solve some of the problems above?
Thanks a bunch.
What will happen if Google starts sending me messages at a rate faster than I can consume?
At the end https://developers.google.com/cloud-messaging/ccs you may read
Conversely, to avoid overloading the app server, CCS stops sending if there are too many unacknowledged messages. Therefore, the app server should "ACK" upstream messages, received from the client application via CCS, as soon as possible to maintain a constant flow of incoming messages. The aforementioned pending message limit doesn't apply to these ACKs. Even if the pending message count reaches 100, the app server should continue sending ACKs for messages received from CCS to avoid blocking delivery of new upstream messages.
In the same document, you find partial answer to your second and third questions
If at any point the connection fails, you should immediately reconnect. There is no need to back off after a disconnect that happens after authentication.
For me it means, that Google implemented a simple redundancy logic and probably not a fair load balancing system (anyway I hope so). If you have that high volumes, I suggest you to contact them directly.
For the last ones, ejabberd is a good product, there are a lot of deployed systems with a clustered infrastructure and a plenty of documents on how do taht. I suggest you to start from here http://docs.ejabberd.im/admin/guide/clustering/ .
Anyway, for your high volumes I would evaluate RabbitMQ which is another Erlang jewel.
ejabberd can be clustered and placed behind a load balancer to distribute connections. A 3 or 4 server cluster should be able to handle that load fine and give you fail over protection. You can add servers if needed. Once you get close to 10 servers you may want to consider using Redis for the in memory DB rather than mnesia.
I have implemented a home monitoring and control system with some motion detectors and temperature sensors, that is connected to a mini PC as a server. On this PC I have a .NET ASMX web service that has some methods, return the detectors situation and environment temperature.
In order to achieve the devices situation I am trying to build an Android application that can connect to the web service via Wifi and shows the temperatures.
when the temperature exceeds critical range or motion detectors detect motion, this application must show a related notification.
The problem here is: every time I need the system situation, I query the web service. but this way I have to query the web service every one second to know that whether the temperature exceeded critical range or not, and whether the detectors detected motion or not.
The question: is there any better solution to achieve this? or is there any way that a web service can inform the clients when an event occurs?
note that I am using KSOAP2 library in my android app.
Thanks in advance
You need to consider using a Push notification pattern instead of polling the server to check for new data.
There are a few options here. The easiest and most standard would be to look into Google's push notification system, called Google Cloud Messaging (GCM) Note that this is only available to devices which have Google Services (so if you're using a Kindle Fire for example, you can't use it)
Or you could consider a more bespoke version of push notifications based on MQTT protocol. You'll need to setup your own MQTT server, and have android code and server code which talks to the MQTT server.
Any time the data changes, you would send a push notification to the subscribing clients so they would not have to be checking for data all the time.
Push services, i.e. http://developer.android.com/google/gcm/index.html
But there is a certain limit of pushes, I guess each second call would kill that limit. Maybe just send requests each 5 seconds, or 10 seconds? Temperature in the room doesn't change even at that rate :)
What's the best way to send constantly updating data from a server (over a REST API or a socket) to an iOS or Android app? Should I create a socket connection and have a socket server that pumps out data, or should I have the app periodically poll a backend resource? Thanks!
Should I create a socket connection and have a socket server that
pumps out data
This is an option. I know some top apps on the play store that use web sockets for streaming data.
Have the app periodically poll a backend resource
I would recommend against this. Polling drains the battery. The android OS will keep the CPU in idle mode at times and constant polling can wake the CPU up and cause a drain in battery. Users wont like that. You are also wasting processing power when there are no results from the server.
The easiest way to send push notifications / minor updates to the android phone is via GCM. The GCM messages are delivered in near real-time (I noticed a lag of about a second for my apps). The payload is limited to 4k and the messages are stored for up to 4 weeks. This is another option you can consider based on your use case.
The typical model I follow is to hit the server on a specified interval and download the updated data.
Polling is bad, it drains out the battery
If you want to update the screen when the application is in the foreground, it is better to go with Socket Connection. You can see the changes in realtime.
For this, you need to create a socket server and open a connection between the device and the server.
https://www.raywenderlich.com/3437391-real-time-communication-with-streams-tutorial-for-ios
I would suggest to use MQTT protocol to publish and subscribe data. Libraries for iOS(Moscapsule) and Android(Paho) for integrating MQTT protocol are available and can easily be integrated in mobile apps.
Backend needs to be configured to support MQTT also. Detail information about how MQTT works can be found here.
I am going to paste my accepted answer from a similar question that was posted a few hours ago.
It can be done using sockets or polling the server but I wouldn't recommend either for a production level app. You will eventually need security features and as a frontend developer, it would be difficult to start from scratch.
I would suggest using a third party service. Take a look at Space Cloud. It is an open source alternative to Firebase where you can use your own database and has built in security features. If you want to go deeper, it uses Apache Kafka for realtime database features.
If those don't suit you then the best option would be to go with GCM.
should I have the app periodically poll a backend resource?
this must be the last option to put in consideration. as long as the client number increases you need to scale out backend/server and this is not as simple as putting an another server next to existing one.
the perfect solution will be a push oriented design and best approach will be to register clients to events and server will push clients if that specific events occur.
you need to be more specific about your business case. you had mentioned real-time in your question but what kind of real-time is that. is it a video streaming, chat application or just ordinary rest calls?
Typically, you'll want your server to push updates to the clients because polling is expensive, may not scale well with N number of clients, and will drain your phone batteries faster. Depending on your server technology:
.NET/Core:
May want to take a look at SignalR to push notifications from the backend to your client apps.
Java:
May want to take a look at Atmosphere to push notifications from the backend to your client apps.
I have used SignalR with good results publishing to phone clients. Have not used Atmosphere, but it has good reviews.
I recently learned about the ability of iPhone apps to receive nearly instantaneous notifications to apps notifications to apps.
This is provided in the form of push notifications, a bespoke protocol which keeps an always on data connection to the iPhone and messages binary packets to the app, which pops up alerts incredibly quickly, between 0.5 - 5 seconds from server app send to phone app response time. This is sent as data - rather than SMS - in very very small packets charged as part of the data plan not as incoming messages.
I would like to know if, using Android, there is either a similar facility, or whether it's possible to implement something close to this using Android APIs. To clarify, I define similar as:
Not an SMS message, but some data driven solution
As real time as is possible
Is scalable, i.e., as the server part of a mobile app, I could notify thousands of app instances in seconds
I appreciate the app could be pull based, HTTP request/response style, but ideally I don't want to be polling that heavily just to check for notification; besides which it's like drip draining the data plan.
Firebase Cloud Messaging FCM FAQ is the new version of GCM. It inherits GCM’s core infrastructure to deliver messages reliably on Android, iOS and Chrome. However they'll continue to support GCM because lot of developers are using GCM SDKs today to handle notifications, and client app upgrade takes time.
As of June 26, 2012, Google Cloud Messaging is the preferred way of sending messages to applications running on devices.
Previously (and now deprecated), the service was called Cloud To Device Messaging.
XMPP is a good solution. I have used it for a push enabled, realtime, Android application. XMPP is powerful, highly extensible and easy to integrate and use.
There are loads of free XMPP servers (though out of courtesy you shouldn't abuse them) and there are open source servers you can run on one of your own boxes. OpenFire is an excellent choice.
The library you want isn't Smack as noted above, it's aSmack. But note, this is a build environment - you will have to build the library.
This is a calculation I did on battery life impact of an XMPP solution:
The Android client must maintain a persistent TCP connection by waking up periodically
to send a heartbeat to the XMPP server.
This clearly imposes a cost in terms of power usage. An estimate of this cost is
provided below:
Using a 1400mAh battery (as supplied in the Nexus One and HTC Desire)
An idle device, connected to an 3G network, uses approximately 5mA
The wake-up, heartbeat, sleep cycle occurs every 5 minutes, takes three seconds
to complete and uses 300mA
The cost in battery usage per hour is therefore:
36 seconds 300mA = 3mAh sending heartbeat
3600 seconds 5mA = 5mAh at idle
4:95 + 3 = 7:95mAh combined
A 1400mAh battery lasts approximately 11.6 days at idle and 7.3 days when
running the application, which represents an approximate 37% reduction in
battery life.
However, a reduction in battery life of 37% represents the absolute worst case
in practice given that devices are rarely completely idle.
I recently started playing with MQTT http://mqtt.org for Android as a way of doing what you're asking for (i.e. not SMS but data driven, almost immediate message delivery, scalable, not polling, etc.)
I have a blog post with background information on this in case it's helpful http://dalelane.co.uk/blog/?p=938
(Note: MQTT is an IBM technology, and I should point out that I work for IBM.)
Have a look at the Xtify platform. Looks like this is what they are doing,
Google is depreciating C2DM, but in its place their introducing GCM (Google Cloud Messaging) I dont think theirs any quota and its free! It does require Android 2.2+ though! http://developer.android.com/guide/google/gcm/index.html
If you can depend on the Google libraries being there for you target market, then you may want to piggy back on GTalk functionality (registering a resource on the existing username - the intercepting it the messages as they come in with a BroadcastReceiver).
If not, and I expect you can't, then you're into bundling your own versions of XMPP. This is a pain, but may be made easier if XMPP is bundled separately as a standalone library.
You may also consider PubSubHubub, but I have no idea the network usage of it. I believe it is built atop of XMPP.
I have been looking into this and PubSubHubBub recommended by jamesh is not an option. PubSubHubBub is intended for server to server communications
"I'm behind a NAT. Can I subscribe to a Hub? The hub can't connect to me."
/Anonymous
No, PSHB is a server-to-server
protocol. If you're behind NAT, you're
not really a server. While we've
kicked around ideas for optional PSHB
extensions to do hanging gets ("long
polling") and/or messagebox polling
for such clients, it's not in the core
spec. The core spec is
server-to-server only.
/Brad Fitzpatrick, San Francisco, CA
Source: http://moderator.appspot.com/#15/e=43e1a&t=426ac&f=b0c2d (direct link not possible)
I've come to the conclusion that the simplest method is to use Comet HTTP push. This is both a simple and well understood solution but it can also be re-used for web applications.
There is a new open-source effort to develop a Java library for push notifications on Android, using the Meteor comet server as a backend. You can check it out at the Deacon Project Blog. We need developers, so please spread the word!
Google recently(18May2016) announced that Firebase is now it's unified platform for mobile developers including near real time push notifications.It is also multi-platform :
The company now offers all Firebase users free and unlimited
notifications with support for iOS, Android and the Web.
source
I cannot find where I read it at, but I believe gmail utilizes an open TCP connection to do the e-mail push.
As GTalk is gone from the SDK, it might be a good idea to make a 'standard' push messaging system. That way, only one service has to run, only one extra tcp connection needs to be open. Applications should talk to this service using Intents and should first request permission to send and receive notification from the service. The service should then notify the user a new application wants to send and receive messages. The user will then grant or deny permission, so he stays in control. The application will then register an action + category to the service, so the service knows how to deliver the pushed message.
Would the a good idea or not?
Why dont you go with the XMPP implementation. right now there are so many public servers available including gtalk, jabber, citadel etc. For Android there is one SDK is also available named as SMACK. This we cant say a push notification but using the XMPP you can keep a connection open between client and server which will allow a two way communication. Means Android client and server both can communicate to each other. At present this will fulfill the need of Push in android. I have implemented a sample code and it really works great
I have recently developed http://pushdroid.org its a single application that should be installed on the phone just like google has implemented it in 2.2 this works from 1.5 and is broadcasting via intent.
The problem with GCM is that there is a lot of configuration involved in the process:
You have to add a lot of boilerplate to you Android app
You need to configure an external server to comunicate with the GCM server
You will have to write tests
If you like simple things (like me) you should try UrbanAirship. It is (IMHO) the easiest way to use GCM in your app without doing a lot of configuration. It also gives you a pretty GUI to test that your GCM messages are being delivered correctly.
You can find the docs and getting started guide here
You can find a sample application here
Note: I am not afiliated with UrbanAirship in any way
https://github.com/Guti/Google-Cloud-Messaging--Titanium-/blob/master/src/com/google/android/gcm/GCMRegistrar.java
Its reaily good and working solution for push.
Please try it
They have their listeners which has to be used by you by using their library classes in your code. You need not to bother about pushing. You have to send the message to server server will push the message to the device. They use OAuth. Regarding Protocols, there are two methods using CCS and XMPP. CCS just uses XMPP as an authenticated transport layer, so you can use most XMPP libraries to manage the connection. To send notifications to device you can write code in android app to send as well as your server code. the message sending will be done only by your code. Rest will be taken care by Google Server in GCM case. You can check detail at this link
http://developer.android.com/google/gcm/server.html
Also, for security issues
google cloud messaging security https://groups.google.com/forum/#!topic/android-gcm/M-EevBitbhQ
In case your app is not running then also devices can recieve notification because you have to write code for broadcast listeners. In background it will be listening to server and whenever any message packet will be there it will recieve the message as notification. Android has service you need to not to bother about it. You have only to use those resources using the library class that makes your work easier and let them write if your app is not running then also it recieve notification. Obviously, there would be some listener whick make the app to recieve.Check "Recieve the message" section in this link
http://developer.android.com/google/gcm/client.html
It will acccept request from users also. For GCM it will do. Please check "Send a message"
http://developer.android.com/google/gcm/client.html