I have a small application, which is free for personal use, but requires a paid license for corporate use.
It is most likely that in a corporate environment my application will run on multiple workstations. If it is the freeware version, I want to show an unobtrusive message. (and continue)
It doesn't have to be bulletproof, if it is not possible (i.e. firewall) then the application should just continue. And I don't want to make the user set up some kind of central service to track the instances. I don't want to annoy my users (especially not the paying ones *g*)
Is there any way to achive this kind of functionality?
I remember an older version of Dreamweaver had this kind of feature. You couldn't run it more than once in the same network.
One way: Listen for UDP broadcast on specific ports. Let each instance send broadcast UDP packet on this port to local network. If application receives such packet, and recognizes its structure, it knows that other instance is running.
You can include license details to avoid messages if two valid licenses are used.
Broadcasts usually aren't routed, so this works on local network only. (And user can disable it completely via firewall too... but if you will use some standard port like 53 (DNS), it won't be blocked).
Other way is to use custom server, which is informed about all running instances around the world ;-)
There are two primary ways to achieve this:
First, you can set up a small server application on each workstation that communicates with other workstations on the network (personally I would use Bonjour for discovery, but there are other options). The drawback here is that you're going to write quite a bit more code to make this work than option #2.
Second (probably simpler) would be to use WMI to enumerate processes on other workstations (again, probably use a Bonjour-like system for discovery), and find your process running on other machines. The drawback to this is that your enumeration code will require privileges on all machines to conduct the search.
When the application starts, it sends out a UDP broadcast on a specific port. This will be restricted to the local subnet, and might not make it through firewalls. This is the "is anyone else running, or can I start?" query.
If there are no responses, the application starts as normal, listening for this UDP broadcast. If it sees one, it responds with an "I'm already running; you can't start" packet.
The application that's just started receives this response packet and then refuses to start or (if you don't want to be that strict) displays a warning to the user.
You'd want to include the product ID and license key (or a hash) in the initial request, so that you can have more than one license on the same network. The response probably wants the machine name in it, so that the second user can go and find the first user and ask if they really need to use the application.
Evil corporation solution:
Have the application call home every time it starts. If more than one application for a license wakes up, tell it not to. If there is no internet connection, don't start at all.
Related
I have a concox GT06 device from which I want to send tracking data to my AWS Server.
The coding protocol manual that comes with it only explains the data structure and protocol.
How does my server receive the GPS data collected by my tracker?
Verify if your server allows you to open sockets, which most low cost solutions do NOT allow for security reasons (i recommend using an Amazon EC2 virtual machine as your platform).
Choose a port on which your application will listen to incoming data, verify if it is open (if not open it) and code your application (i use C++) to listen to that port.
Compile and run your application on the server (and make sure that it stays alive).
Configure your tracker (usually by sending an sms to it) to send data to your server's IP and to the port which your application is listening to.
If you are, as i suspect you are, just beginning, consider that you will invest 2 to 3 weeks to develop this solution from scratch. You might also consider looking for a predeveloped tracking platform, which may or may not be acceptable in terms of data security.
You can find examples and tutorials online. I am usually very open with my coding and would gladly send a copy of the socket server, but, in this case, for security reasons, i cannot do so.
Instead of direct parsing of TCP or UDP packets you may use simplified solution putting in-between middleware backends specialized in data parsing e.g. flespi.
In such approach you may use HTTP REST API to fetch each new portion of data from trackers sent to you dedicated IP:port (called channel) or even send standardized commands with HTTP REST to connected devices.
At the same time it is possible to open MQTT connection using standard libraries and receive converted into JSON messages from devices as MQTT in real time, which is even better then REST due to almost zero latency.
If you are using python you may take a look at open-source flespi_receiver library. In this approach with 10 lines of code you may have on your EC2 whole parsed into JSON messages from Concox GT06.
Is there any protocol, API or software in existence that can send data/IM/etc directly from one device to another with no server?
Can you not use HTTP GET/POST/DELETE directly between two devices when their device data is known to the user(s)?
I would very much like to know if there is ANY software/protocols that can do this.
thank you!
The internet is build on the Internet Protocol suite. This suite has 5 different layers of protocols: The physical layer, the link layer, the network layer, the transport layer and the application layer. Each depends on the one before.
If you just use the browser, by default HTTP (application layer) is used, which relies on TCP (transport layer), which relies on IP (v4 or v6, network layer), which relies on ethernet (link layer), which finally relies on the actual cable that's plugged into your computer (for WiFi, the first three are the same but the last two differ if I'm not mistaken).
Now to your question: Is there any protocol, API or software in existence that can send data/IM/etc directly from one device to another with no server?
Yes there is. I suggest you start looking at protocols that are in the application layer. To highlight a few standards next to HTTP(S): FTP is for file transfer, IMAP is for emails clients, SMTP is for email servers and SSH is a secure shell which can also be used to tunnel data through.
For your specific case, I think either FTP (FTPS if you want it over SSL), or SSH can be a solution, but it's hard to know for sure without the specifics.
The only thing that these protocols have in common is that one of the two computers will act like server and the other computer as client. This has as downside that port-forwarding might be necessary.
If you've chosen the protocol you'd like to use, then you're up for the next step, selecting a program that can do that for you. For HTTP(S), I'd recommend Apache. If you're using Linux and chose SSH, then you're in luck, there is a build in SSH server in Linux, you can use that. For other protocols, you might just want to search yourself, as I do not have any suggestions.
I hope this answers most of your questions!
Desirius
In browser context, WebRTC is probably what you are looking for: It allows user to user communications.
https://en.wikipedia.org/wiki/WebRTC
https://webrtc.org/
That is to say, if I have a server listening on 127.0.0.1, and a TCP connection comes in, how can I determine the process id of the client?
Also if there isn't an API for this, where would I be able to extract the information from in a more hackish manner?
(The purpose of this is to modify a local HTTP proxy server to accept or deny requests based on the requesting process.)
Edit: palacsint's answer below led me to find this answer to a similar question which is just what's needed
netstat -a -o
prints it. I suppose they are on the same machine becase you are listening on 127.0.0.1.
The only way to do this is if the connecting process sends some sort of custom headers which contains identifier. This is due to the fact that the networking layer is completely separated from the application layer (hint: OSI MODEL. This way it is possible to write lower layers software without caring what happens above as long as the messages exchanged (read: networking packets) follow a pre-determined format (read: use the same protocol).
If a regular internet user wishes to contact a TCP service on their computer but without having to go through the hassle of firewall translation I think I'm right in saying that the 'best' way to do this is by having a 3rd party in the middle that will accept connections from both the user's home computer and their travelling computer and act as a proxy.
But how exactly is this achieved? Obviously the travelling computer just contacts the proxy server whenever it wants information, but how is this then relayed back to the home computer? Does the home computer keep a constant connection open with the proxy which allows bidirectional data flow?
If this is the case, how would I go about designing a Ruby/Sinatra server that would keep track of these permanent connections and then forward a travelling computer's queries onwards? (Assume that the home computer's service can make whatever calls would be necessary to establish the link)
Thanks guys!
EDIT
I think I over-generalised, I'm forwarding HTTP requests (or at least, the requests coming from the travelling computer will be HTTP based), so I figured it made sense to use sinatra to capture the requests from the traveller. My problem though is how to keep an open connection from the home computer to the proxy so I can forward the requests immediately.
I know persistent HTTP connections can be done, but that they're a little convoluted, would I be better off having the home computer continually establish a lower level connection with the proxy and push the requests over that?
I think your general methodology will work - relay event messages from one computer to another by having the traveling computer send signals to the proxy and having the home computer request new information from the proxy.
If you want more continuous data flow, you may not want to use sinatra - specifically for receiving the data from the travelling computer. Check out Event Machine - https://github.com/eventmachine/eventmachine/wiki
Windows NLB works great and removes computer from the cluster when the computer is dead.
But what happens if the application dies but the server still works fine? How have you solved this issue?
Thanks
By not using NLB.
Hardware load balancers often have configurable "probe" functions to determine if a server is responding to requests. This can be by accessing the real application port/URL, or some specific "healthcheck" URL that returns only if the application is healthy.
Other options on these look at the queue/time taken to respond to requests
Cisco put it like this:
The Cisco CSM continually monitors server and application availability
using a variety of probes, in-band
health monitoring, return code
checking, and the Dynamic Feedback
Protocol (DFP). When a real server or
gateway failure occurs, the Cisco CSM
redirects traffic to a different
location. Servers are added and
removed without disrupting
service—systems easily are scaled up
or down.
(from here: http://www.cisco.com/en/US/products/hw/modules/ps2706/products_data_sheet09186a00800887f3.html#wp1002630)
Presumably with Windows NLB there is some way to programmatically set the weight of nodes? The nodes should self-monitor and if there is some problem (e.g. a particular node is low on disc space), set its weight to zero so it receives no further traffic.
However, this needs to be carefully engineered and have further human monitoring to ensure that you don't end up with a situation where one fault causes the entire cluster to announce itself down.
You can't really hope to deal with a "byzantine general" situation in network load balancing; an appropriately broken node may think it's fine, appear fine, but while being completely unable to do any actual work. The trick is to try to minimise the possibility of these situations happening in production.
There are multiple levels of health check for a network application.
is the server machine up?
is the application (service) running?
is the service accepting network connections?
does the service respond appropriately to a "are you ok" request?
does the service perform real work? (this will also check back-end systems behind the service your are probing)
My experience with NLB may be incomplete, but I'll describe what I know. NLB can do 1 and 2. With custom coding you can add the other levels with varying difficulty. With some network architectures this can be very difficult.
Most hardware load balancers from vendors like Cisco or F5 can be easily configured to do 3 or 4. Level 5 testing still requires custom coding.
We start in the situation where all nodes are part of the cluster but inactive.
We run a custom service monitor which makes a request on the service locally via the external interface. If the response was successful we start the node (allow it to start handling NLB traffic). If the response failed we stop the node from receiving traffic.
All the intermediate steps described by Darron are irrelevant. Did it work or not is the only thing we care about. If the machine is inaccessible then the rest of the NLB cluster will treat it as failed.