I have application where clients are two.
1 > Device (socket.io)
2 > Angular (socket.io)
My application is working fine with one server but when I have put in scalable mode then it create problem to make communication between device and angular (socket).
So basically, we need solution where once device connected to a server then some middleware(like haproxy) will help to send all request after that to that particular server only.
Application Uses:
Node
Socket io
Python
Angular
Hosted on AWS and uses : EC2,Elastic cache Redis, DynamoDB
Please let me know if you have any query from my question.
Thanks in advance!
Related
I have a device (esp32s2) which is IoT enabled and communicating with AWS server.
The device is connecting to the internet via router. I want to check from the device, if the router is connected to the internet or not. If not connected, I need to disconnect mqtt broker instantly.
I know there is aws_iot_yield happening, but it is taking too much of time to change the client state (~5-10 mins) after disconnection. So, is there is any other way in which I can come to know if the device is connected to the mqtt broker or not using AWS sdk?
I want to avoid using pinging to some address/server as it will increase the usage of resources.
Thanks in advance!
Since the connectivity to the AWS server trough internet depends on the network elements, the only reliable way to know if you are connected to internet is to send a package to a know address and receive the response. Simplest way to do this is to use ICMP (ping) protocol. Usually the most reliable destination to ping is the Google DNS server 8.8.8.8 or 8.8.4.4 which is a cluster service and it's always replying on the ping.
You can control the pause between two pings and how many pings you will send in one session in order to preserve the resources.
Alternative approach is to use a router that can send messages to a monitoring device that the link state was changed (by example SNMP trap). But this is not fully reliable method since the router can not detect all scenarios where the connectivity to your AWS server is lost.
I'm trying to figure out how to create an offline / online approch to use within a huge application.
Right now, each part of the application has its own model and datalayer, who directly read / write data from / to SQL. My boss is asking me to create a kind of buffer that, in case of connectivity failure, might be used to store data until the connection to SQL return active.
What I'm trying to create is something like this: move all datalayers into a servicestack service. Each "GET" method should query the database and store the result into a cache to be reused once the connection to SQL is not available. Each "POST" and "PUT" method must execute their actions or store the request into a cache if the connection fail. this cache must be cleared once the connection to SQL is restored.
How can I achieve this? Mine is a WPF application running on Windows 10.
Best regards
Enrico
Maintaining caches on the server is not going to help create an offline Application given the client wouldn't have access to the server in order to retrieve those caches. What you'd need instead is to maintain state on the client so in the event that network access is lost the client is loading from its own local caches.
Architecturally this is easiest achieved with a Web App using a Single Page App framework like Vue (+ Vuex) or React (+ Redux or MobX). The ServiceStack TechStacks and Gistlyn Apps are good (well documented) examples of this where they store client state in a Vuex store (for TechStacks created in Vue) or Redux Store (for Gistlyn created in React), or the Old TechStacks (created with AngularJS).
For good examples of this checkout Gistlyn's snapshots feature where the entire client state can be restored from a single serialized JSON object or approach used the Real Time Network Traveler example where an initial client state and delta's can be serialized across the network to enable real-time remote control of multiple connected clients.
They weren't developed with offline in mind, but their architecture naturally leads to being offline capable, courtesy of each page being first loaded from its local store then it fires off a Request to update its local cache which thanks to the reactivity of JS SPA fx's, the page is automatically updated with the latest version of the server.
Messaging APIs
HTTP has synchronous tight coupling which isn't ideal for offline communication, what you want instead is to design your write APIs so they're One Way/Asynchronous so you can implement a message queue on the client which queues up Request DTOs and sends them reliably to the server by resending them (using an exponential backoff) until the succeed without error. Then for cases where the client needs to be notified that their request has been processed they can either be done via Server Events or via the client long-polling the server checking to see if their request has been processed.
I have this admin panel template that's built in nodejs, jquery and angular.
I am trying to connect it to a mongodb to make simple CRUD operations.
I've installed mongojs via npm for this purpose but how do I take it from here? The Datebase itself is already set up and ready for use.
I tried to follow the instructions but I am not quite sure where to put the code that connects to the database.
var databaseUrl = "mydb"; // "username:password#example.com/mydb"
var collections = ["users", "reports"]
var db = require("mongojs").connect(databaseUrl, collections);
I've understood that it has to be on the server side as the client side won't run the require('mongojs') part. But in what file should it preferably be placed? And if it's put in the server side code how do I reach the 'db' object from the client side when making the CRUD operations?
Thanks in advance!
The server and the clients are different devices that interact by HTTP. Consider them as different projects that can luckily execute same chunks of code just because they are written in the same language. DB connection is not this kind of chunk.
Client doesn't connect to the database. You can't give db access to all your clients. Actually db should not be accessible from the Internet at all for security reasons.
Client makes HTTP requests to the server. Server fetches the db data and returns it back to the client. It is the main purpose of almost all servers.
This data updates the state of the models in your controller code.
I'm writing a simple XMPP chat application. The interface has been made minimal to accommodate mobile devices. The client uses strophe.js which utilizes a bi-directional persistent connection (BOSH) between the javascript application and XMPP server.
Would this persistent connection consume a lot of bandwidth? I know most mobile phone users have some sort of monthly data quota - I don't want to hog it.
Yes, if you do the math, you need to account for:
HTTP headers sent & received
Possible cookies to/from the server
BOSH typically sends a packet every minute both ways (called the empty body). This takes up considerable bandwidth.
You might want to consider using websockets instead.
http://blog.superfeedr.com/xmpp-over-websockets/
Is there an open source WebSockets (JavaScript) XMPP library?
The XEP (draft): https://datatracker.ietf.org/doc/html/draft-moffitt-xmpp-over-websocket-00
I wonder how can I achieve this without UDP, I have a solution using UDP multicast: http://blogs.msdn.com/b/ncl/archive/2009/11/18/udp-multicast-in-silverlight-4.aspx
but since this is for a high profile customer who has an intranet with port TCP 80 and TCP 8080 only enabled this solution is not possible. Yes, the application runs in an intranet environment.
I need a simple example how to send messages to all Silverlight clients over WCF.
I found this solution, but I have no idea how to implement that into Silverlight:
http://idunno.org/archive/2008/05/29/wcf-callbacks-a-beginners-guide.aspx
I'm out of ideas guys, please help.
Instead of receiving notifications async the Silverlight client should use polling instead.
It can poll a WCF service that will fetch the data from a db...
This is the typical solution. Anyway, you have to handle the case in which the Silverlight client wasn't online and then it becomes online and need to know its state...
However, if you still want Silverlight to receive async notifications try searching for 'Full Duplex'.
Here are some starting points:
http://blog.developers.ba/post/2009/02/25/Silverlight-chat-application-using-WCF-full-duplex.aspx
http://weblogs.asp.net/dwahlin/archive/2008/06/16/pushing-data-to-a-silverlight-client-with-wcf-duplex-service-part-i.aspx
http://hindams.wordpress.com/2010/04/05/wcf-full-duplex-with-a-silverlight-application/