I am trying to solve the following problem and was wondering what is the best approach to apply?
I'd like to setup a versioned communication via ZeroMQ, which effectively means that any client first makes a handshake stating the version of its messaging protocol and than all subsequent requests are forwarded only to specific set of workers, i.e. the ones which can understand this protocol.
I saw the example of Router/Dealer but there forwarding occurs always to all workers.
IMO this is something like a session, which is established based on handshake and all future requests are made in a particular context. Can this be done with ZeroMQ?
I understand that I can send back some ID to the client and ask it to put in all future requests, but would like to avoid that kind of intrusiveness.
Just a side note: I implement this approach in C++. I don't mind if you answer represents a general idea taking in account features available in either in ZeroMQ C API or cppzmq wrapper. No need to write a fully fledged solution, just how it might be done.
Yes, this seems doable:
With a full respect not to enter into "in-band" signalling via ID/multipart message-processing, one may build the wish-to-have infrastructure using a mix of static and dynamic use of as-is ZeroMQ resources.
Step 0: your central authority handles initial "client" contact / handshaking / identity validation
Step 1: each "client" receives a set of directions, as it's identity/version got approved, based upon 0)
Step 2: ad-hoc instructed "client" may { .connect() | .bind() } with appropriate access-point
Step 3: as an architecture bonus, this can be enjoyed as distributed platform with re-negotiation(s) and node re-discoveries for even more robust, scalable-performance and raised security motivated scenarios
Our own imagination is the only ceiling:
In a few word, one may soon forget about the standard Scalable Formal Communication Patterns, these serve as rather a set of building blocks for ad-hoc defined architectures. That is the biggest power of the ZeroMQ or nanomsg to realise.
May read more on advanced use-cases in this ( and check the book there ... ).
Related
I am trying to build a c++ application that must use ZeroMQ to listen to encoded packets being forwarded to port 8080 via UDP on my machine at a rate of 10 [Hz].
How do I setup a zmq socket/server/etc.. such that I can receive and decode the incoming data?
I am on a linux machine, running Ubuntu 16.04
UPDATE + ANSWER:
ZMQ does not listen to generic UDP packets, as #tadman stated. Therefore, considering I was unable to modify the system that was sending the packets, this would not be an appropriate use for ZMQ. I ended up using a generic UDP endpoint as #tadman recommended.
How do I use ZeroMQ to listen to and parse UDP-data on a specific port ?
Greetings to Dearborn/UoM, let's first demystify the problem, ok?
ZeroMQ is not a self-isolating tool, it can and does talk or listen to non-ZeroMQ sockets too.
#tadman was right and wrong at the same time.
ZeroMQ doesn't listen to UDP packets. // == True; ( as of known in 2018-Q2, API ~ 4.2.2 )It listens to ZeroMQ packets. // == False;
Since ZeroMQ native API ~ 4.+, ZeroMQ can both listen and talk to non-ZeroMQ sockets, i.e. your wish may lead to a ZeroMQ Context()-engine working with a plain socket.
If new to ZeroMQ distributed-system's design eco-systems, you may like first a brief dis-ambiguation read into the main conceptual differences in the [ ZeroMQ hierarchy in less than a five seconds ] Section, so as to better touch the roots of the problem to solve.
ZeroMQ has udp:// <transport-class>,can be used for { ZMQ_RADIO | ZMQ_DISH } Archetypes only
While ZeroMQ has the udp:// transport-class ready to use for both unicast and multicast AccessPoint addresses, it is not yet possible to make the Context() instantiate such data-pump for a non-ZeroMQ, plain-socket peers.
ZeroMQ can talk to non-ZeroMQ peers,yet just over a tcp:// <transport-class>
non-ZeroMQ peers can get connected using a plain socked, redressed ( due to many architecture / API design reasons ) inside the ZeroMQ implementation into a ZeroMQ-compliant Scalable Formal Communication Archetype named ZMQ_STREAM ). This is cool and permits to use homogeneous strategies to handle also these types of communicating peers, yet, there is just a need to use the tcp:// transport-class, if this is necessary.
How to ?
Given your source of the dataflow is under your control, try to make it use ZeroMQ eco-system, since which it can be comfortably served as any other ZeroMQ udp://-cross-connected AccessPoint.
If design or "political" constraints prevent you from doing so, the receiving side cannot be ZeroMQ directly, so decide about making an application-specific protocol gateway, mediating Non-ZeroMQ-udp traffic to any form of ZeroMQ "consumable", be it a ZMQ_STREAM over plain-tcp: ( if decided to make a functionally minimalistic design of the proxy, or decide to equip such proxy straight with any other, smarter ZeroMQ archetype, to communicate on way higher level of comfort with your main data-collector / processor ).
If audio is the intended payload and the accumulating latency is a concern, best also read more details on how easily the main engine can get performance tuned - scaled up the number of IOthreads, wisely mapped ZMQ_AFFINITY and ZMQ_PRIORITY settings - all that can influence the target latency + throughput performance envelopes.
Last, but not least, the 10 [Hz] requirement
this one is indeed a nice part, that will test one's insights into asynchronous process coordination. ZeroMQ main engine ( the Context()-instance(s) ) work in an asynchronous and uncoordinated manner.
This means, there is no direct way to avoid accumulated latency or to inspect any of the Broker-less, per-peer managed, async by desing message-queue buffer, so as to "travel"-"back"-in-time, upon a Hard-Real-Time 10 [Hz] probing.
If this is going to work in a weak / "soft" ( not a strict R/T ) flow-of-time system coordination ( having no control-system stability constraints / critical-system / life-supporting or similar system responsibility, as hard R/T system designs do have ), thus tolerating a certain amount of code-execution related jitter RTT- / [ transport + (re-)processing ]-latencies a smart-designed .poll()-based non-blocking inspections and possibly some fast queue pre-emptying policies may help you get into acceptably fast, soft-RT behaviour to make the 10 [Hz]-monitor robust enough.
So, indeed cool days with ZeroMQ in front of you - Good Luck, Sir. If not already overdue with Project's Plan or deadline coming on Monday, best take a read of a fabulous Pieter HINTJENS' book "Code Connected, Volume 1", where most gems of the Zen-of-Zero are well discussed and inspected for distributed-systems designs.
I am implementing a c++ application which involves multiply users(for example. 128 users) with asymmetric roles(they all have different jobs). In such scenario, every user has to communicate with each other. Thus each pair of users need a bi-direction (virtual) communication channel between them.
There are three popular messaging patterns in this application.
Exchange: each user i has a message m_ij for user j != i to send. The length of m_ij is a public constant value. These messages m_ij are independent and have no relation with each other. This is something like "everyone has something for everyone".
Distribute: a (per-determined) user i_0 has a message m_j for ever other user j!=i_0. The length of the messages is a public constant value. It is a little similar to broadcast but the receivers are not receiving the same message.
Gather: a (per-determined) user i_0 receives a message m_j from ever other user j!=i_0. The length of the messages is a public constant value. This is very similar to vote mechanism.
Besides, there are also a small amount of two-party communication between some of the users.
The round-trip cost is very sensitive in the application. Thus a one-roundtrip implementation for these communication patterns is very desirable.
Besides, the bandwidth cost of the application is very high thus a non-blocking implementation is almost a must-have.
I first tried the classic server/client socket (https://www.geeksforgeeks.org/socket-programming-cc/) by having multiply ports and deploy a server/client pair between every two users. However it turns out to be a failure.
I also investgate the ZMQ library. But to my poor understanding I have to somehow handle "routing" on my own, which I am not capable of.
Nanomsg is another candidate to go with but none of the patterns it provides seem to match the requirements.
So, could anyone provide any idea about this challenge? Thanks in advance!
I am looking to use ZeroMQ to facilitate IPC in my embedded systems application, however, I'm not able to find many examples on using multiple 0MQ socket types in the same process.
For example, say I have a process called "antenna_mon" that monitors an antenna. I want to be able to send messages to this process and get responses back - a classic REQ-REP pattern. However, I also have a "cm" process, that publishes configuration changes to subscribers. I want antenna_mon to also subscribe to antenna configuration changes - PUB-SUB.
I found this example of reading from multiple sockets in the same process, but it seems sub optimal, because now you no longer block waiting for messages, you inefficiently check for messages constantly and go back to sleep.
Has anyone encountered this problem before? Am I just thinking about it wrong? Maybe I should have two threads - one for CM changes, one for REQ-REP servicing?
I would love any insights or examples of solving this type of problem.
Welcome to the very nature of distributed computing!
Yes, there are new perspectives one has to solve, once assembling a Project for a multi-agent domain, where more than one process works and communicates with it's respective peers ad-hoc.
A knowledge base, acquired from a soft Real-Time System or embedded systems design experience will help a lot here. If none such available, some similarities might be also chosen from GUI design, where a centerpiece is something like a lightweight .mainloop() scheduler, and most of the hard-work is embedded into round-robin polled GUI-devices and internal-state changes or external MMI-events are marshalled into event-triggered handlers.
ZeroMQ infrastructure gives one all the tools needed for such non-blocking, controllably poll-able ( scaleable, variable or adaptively ad-hoc adjustable poll-timeouts, not to overcome the given, design defined, round-trip duration of the controller .mainloop() ) and transport-agnostic, asynchronously operated, message dispatcher ( with thread-mapped performance scaling & priority tuning ).
What else one may need?
Well, just imagination and a lot of self-discipline to adhere the Zero-Copy, Zero-Sharing and Zero-Blocking design maxims.
The rest is in your hands.
Many "academic" examples may seem trivial and simplified, so as to illustrate just the currently discussed, or a feature demonstrated in some narrow perspective.
Not so in the real-life situations.
As an example, my distributed ML-engine uses a tandem of several PUSH/PULL pipelines for moving state data updates transfers and prediction forcasts + another PUSH/PULL for remote keyboard + a reversed .bind()/.connect() on PUB/SUB for easy broadcasting of distributed agents' telemetry to a remote centrally operated syslog and some additional PAIR/PAIR pipes, as processing requires.
( nota bene: one shall always bear in mind, that robust and error-resilient systems ought avoid to use a default REQ/REP Scaleable Formal Communication Pattern, as there is non-zero probability of falling the pairwise-stepped REQ/REP dual-FSA into an unsalvageable deadlock. Do not hesitate to read more about this smart tool. )
I'm looking for a way to add network emulation to a socket.
The basic solution would be some way to add bandwidth limitation to a connection.
The ideal solution for me would:
Support advanced network properties (latency, packet-loss)
Open-source
Have a similar API as standard sockets (or wraps around them)
Work on both Windows and Linux
Support IPv4 and IPv6
I saw a few options that work on the system level, or even as proxy (Dummynet, WANem, neten, etc.), but that won't work for me, because I want to be able to emulate each socket manually (for example, open one socket with modem emulation and one with 3G emulation. Basically I want to know how these tools do it.
EDIT: I need to embed this functionality in my own product, therefore using an extra box or a third-party tool that needs manual configuration is not acceptable. I want to write code that does the same thing as those tools do, and my question is how to do it.
Epilogue: In hindsight, my question was a bit misleading. Apparently, there is no way to do what I wanted directly on the socket. There are two options:
Add delays to send/receive operation (Based on #PaulCoccoli's answer):
by adding a delay before sending and receiving, you can get a very crude network simulation (constant delay for latency, delay sending, as to not send more than X bytes per second, for bandwidth).
Paul's answer and comment were great inspiration for me, so I award him the bounty.
Add the network simulation logic as a proxy (Based on #m0she and others answer):
Either send the request through the proxy, or use the proxy to intercept the requests, then add the desired simulation. However, it makes more sense to use a ready solution instead of writing your own proxy implementation - from what I've seen Dummynet is probably the best choice (this is what webpagetest.org does). Other options are in the answers below, I'll also add DonsProxy
This is the better way to do it, so I'm accepting this answer.
You can compile a proxy into your software that would do that.
It can be some implementation of full fledged socks proxy (like this) or probably better, something simpler that would only serve your purpose (and doesn't require prefixing your communication with the destination and other socks overhead).
That code could run as a separate process or a thread within your process.
Adding throttling to a proxy shouldn't be too hard. You can:
delay forwarding of data if it passes some bandwidth limit
add latency by adding timer before read/write operations on buffers.
If you're working with connection based protocol (like TCP), it would be senseless to drop packets, but with a datagram based protocol (UDP) it would also be simple to implement.
The connection creation API would be a bit different from normal posix/winsock (unless you do some macro or other magic), but everything else (send/recv/select/close/etc..) is the same.
If you're building this into your product, then you should implement a layer of abstraction over the sockets API so you can select your own implementation at run time. Alternatively, you can implement wrappers of each socket function and select whether to call your own version or the system's version.
As for adding latency, you could have your implementation of the sockets API spin off a thread. In that thread, have a priority queue ordered by time (i.e. this background thread does a very basic discrete event simulation). Each "packet" you send or receive could be enqueued along with a delivery time. Each delivery time should have some amount of delay added. I would use some kind of random number generator with a Gaussian distribution.
The background thread would also have to simulate the other side of the connection, though it sounds like you may have already implemented that part?
I know only Network Link Conditioner for Mac OS X Lion. You should be mac developer to download it, so i cannot put download link there. Only description from 9to5mac.com: http://9to5mac.com/2011/08/10/new-in-os-x-lion-network-link-conditioner-utility-lets-you-simulate-internet-and-bandwidth-conditions/
This answer might be a partial solution for you when using linux:
Simulate delayed and dropped packets on Linux. It refers to a kernel module called netem, which can simulate all kinds of network problems.
If you want to work with TCP connections, having "packet loss" could be problematic since a lot of error-handling (like recovering lost packages) is done in the kernel. Simulating this in a cross-platform way could be hard.
you usually add a network device to your network that throttles the bandwidth or latency, on a port by port basis, you can then achieve what you want just by connecting to the port allocated to the particular type of crappy network you want to test, with no code changes or modifications required.
The easiest ways to do this is just add iptables rules to a Linux server acting as a proxy.
If you want it to work without the separate device, try trickle that is a software package that throttles your network on your client PC. (or for Windows)
You may would like to check WANem http://wanem.sourceforge.net/ . WANEM is Open Source and licensed under the GNU General Public License.
WANem allows the application development team to setup a transparent application gateway which can be used to simulate WAN characteristics like Network delay, Packet loss, Packet corruption, Disconnections, Packet re-ordering, Jitter, etc.
I think you could use a tool like Network Simulator. It's free, for Windows.
The only thing to do is to setup your program to use the right ports (and the settings for the network, of course).
If you want a software only solution that you control, you will have to implement it yourself. I know of no such existing package.
While a wrapper layer over a socket may give you the ability to introduce delay, it won't be sufficient to introduce loss or out of order delivery. In order to simulate those activities, you actually need intercept the data in transit between the two TCP stacks.
The approach I would recommend is to use a tunneling device (say tunX). Routes should be set so the client believes the way to the server is through tunX. Additional code (perhaps running in a different thread) would promiscuously intercept traffic on tunX, and perform your augmented behavior, before forwarding packets over the true physical interface that will get the traffic to your server. The reverse would happen for packets arriving from the server on the physical interface. Those packets would be intercepted by the client code, behavior augmented, before forwarding through tunX.
However, since you are testing client software, I am unclear as to why you would want to embed this code in your released software, unless the software itself is a WAN simulating client.
I am coding a workload scheduler. I would like my piece of software to be a peer-to-peer scheduler, ie. a node only knows some neighbours (other nodes) and use them to reach other nodes.
Each node would have its own weighted-routing table to send messages to other peers (basically based on the number of hops), ie. "I want the master to give me my schedule" or "is resource A available on node B ?" : which neighbor is the closest to my target ?
For instance I have written my own routing protocol using XML-RPC (xmlrpc-c) and std::multimaps / std::maps.
I am thinking of using ZeroMQ to optimze my data streams :
queueing can reduce the network load between peers ;
subscriptions can be used to publish upgrades.
As a consequence :
I would need to open as many sockets as I would create new types of connections ;
Each node would need to be a client, a server, a publisher, a subscriber, a broker and a directory ;
I am not sure that my "peer-to-peer architecture" is compatible with the main purpose of ZeroMQ.
Do you think that ZeroMQ can be a helpful concept to use ?
It would be helpful to know exactly what you mean by "routing protocol".
That sounds like you mean the business logic of routing to a particular peer.
Knowing more fully what you're looking to achieve with ZeroMQ would also be helpful.
Have you read the ZeroMQ Guide?
ZeroMQ is a pretty different beast and without spending some time to play with it, you'll
likely find yourself confused. As a bonus, reading the guide will also help you answer
this question for yourself, since you know your requirements better.
ZeroMQ was designed to build robust distributed and multi-threaded applications. Since distributed applications can often take the form of "peer-to-peer", ZeroMQ could indeed be a good fit for your needs.