I need to have an intelligent conversation with several co-workers who have not yet been sold on embracing tried and trusted message queuing libraries such as MSMQ, ZeroMQ, RabbitMQ, etc and we need this type of messaging in our solution.
But to be able to sell to my colleagues the benefits of using established solutions, I need to understand the fundamental difference between PGM and UDP. What is PGM solving that UDP multicast could not solve?
The fundamental difference:
UDP multicast is not reliable meaning messages may be lost or delivered out of order,If you want delivery guarantees you will have to build middleware on top to handle this.On the other hand PGM is a reliable multicast protocol meaning you get in order message delivery guarantees "out of the box" PGM
Related
I am super new to the networking world, so I have a QTcpserver that's currently working with the newConnection signal, but I was wondering if I could use QUdpSocket with a QTcpServer ? It's this possible at all ?
TCP is a connection oriented stream over an IP network. It guarantees
that all sent packets will reach the destination in the correct order.
This imply the use of acknowledgement packets sent back to the sender,
and automatic retransmission, causing additional delays and a general
less efficient transmission than UDP.
UDP is a connection-less protocol. Communication is datagram oriented.
The integrity is guaranteed only on the single datagram. Datagrams
reach destination and can arrive out of order or don't arrive at all.
It is more efficient than TCP because it uses non ACK. It's generally
used for real time communication, where a little percentage of packet
loss rate is preferable to the overhead of a TCP connection.
StackOverFlow
So the simple Answer is No , You can't ,because tcp and udp are 2 different protocols .
I want to develop a program in c using pjsip for peer to peer file transfer. As pjsip uses ice and in ICE UDP is used, so do I need to handle the packet delivery assurance.
And as I would be sending the file by breaking it into several parts and them re assemble all the parts at the receiver's end, so do I have to maintain the sequence of the packets or can i assume that packets are delivered in the correct sequence??
With UDP you can neither assume that packets are delivered in order nor that they are delivered exactly once nor that they are delivered at all! So you need to come up with a protocol that does a lot of things which normally TCP would take care of. It has to reassemble the original data stream and handle the things I listed above.
Additionally, with UDP you can have the problem that you cause congestion. TCP can avoid that with its congestion avoidance algorithms, with UDP you can easily send packets too fast causing them to drop at the overloaded router.
All these are non trivial problems to solve so I suggest you read up on the topic. I'd start with a good book about TCP.
In our application the publisher creates a message and sends it to a topic.
It then needs to wait, when all of the topic's subscribers ack the message.
It does not appear, the message bus implementations can do this automatically. So we are leaning towards making each subscriber send their own new message for the client, when they are done.
Now, the client can receive all such messages and, when it got one from each destination, do whatever clean-ups it has to do. But what if the client (sender) crashes part way through the stream of acknowledgments? To handle such a misfortune, I need to (re)implement, what the buses already implement, on the client -- save the incoming acknowledgments until I get enough of them.
I don't believe, our needs are that esoteric -- how would you handle the situation, where the sender (publisher) must wait for confirmations from multiple recipients (subscribers)? Sort of like requesting (and awaiting) Return-Receipts from each subscriber to a mailing list...
We are using RabbitMQ, if it matters. Thanks!
The functionality that you are looking for sounds like a messaging solution that can perform transactions across publishers and subscribers of a message. In The Java world, JMS specifies such transactions. One example of a JMS implementation is HornetQ.
RabbitMQ does not provide such functionality and it does for good reasons. RabbitMQ is built for being extremely robust and to perform like hell at the same time. The transactional behavior that you describe is only achievable with the cost of reasonable performance loss (especially if you want to keep outstanding robustness).
With RabbitMQ, one way to assure that a message was consumed successfully, is indeed to publish an answer message on the consumer side that is then consumed by the original publisher. This can be achieved through RabbitMQ's RPC procedure calls which might help you to get a clean solution for your problem setting.
If the (original) publisher crashes before all answers could be received, you can assume that all outstanding answers are still queued on the broker. So you would have to build your publisher in a way that it is capable to resume with processing those left messages. This might turn out to be none-trivial.
Finally, I recommend the following solution: Design your producing component in a way that you can consume the answers with one or more dedicated answer consumers that are separated from the origin publisher.
Benefits of this solution are:
the origin publisher can finish its task independent of consumer success
the origin publisher is independent of consumer availability and speed
the origin publisher implementation is far less complex
in a crash scenario, the answer consumer can resume with processing answers
Now to a more general point: One of the major benefits of messaging is the decoupling of application components by the broker. In AMQP, this is achieved with exchanges and bindings that allow you to move message distribution logic from your application to a central point of configuration.
If you add RPC-style calls to your clients, then your components are most likely closely coupled again, meaning that the publishing component fails if one of the consuming components fails / is not available / too slow. This is exactly what you will want to avoid. Otherwise, why would you have split the components then?
My recommendation is that you design your application in a way that publishers can complete their tasks independent of the success of consumers wherever possible. Back-channels should be an exceptional case and be implemented in the described not-so coupled way.
I'm a little confused as to what the difference is between a message broker e.g. RabbitMQ and Message-orientated Middleware. I can't find much info apart from what's on Wikipedia. When searching MOM I find info on AMQP which states is a protocol for MOM.. what does this mean? What is MOM then? I also have read that RabbitMQ implements the AMPQ protocol.. so why does that make a RabbitMQ a messsage broker? Are a message broker and MOM the same thing?
Hope some can unravel my confusion. thanks
An overview -
A protocol - A set of rules.
AMQP - AMQP is an open internet protocol for reliably sending and receiving messages.
MOM (message-oriented-middleware) - is an approach, an architecture for distributed system i.e. a middle layer for the whole distributed system, where there's lot of internal communication (a component is querying data, and then needs to send it to the other component, which will be doing some processing on the data) so components have to share info/data among them.
Message broker - is any system (in MOM) which handles messages (sending as well as receiving), or to be more precise which routes messages to the specific consumer/recipient. A Message Broker is typically built upon a MOM. The MOM provides the base communication among the applications, and things like message persistence and guaranteed delivery. "Message brokers are a building block of Message oriented middleware."
Rabbitmq - a message broker; a MOM implementation; an open-source implementation of AMQP; as per Wikipedia:
RabbitMQ is an open source message broker software (sometimes
called message-oriented middleware) that implements the Advanced
Message Queuing Protocol (AMQP).
As you asked:
When searching MOM I find info on AMQP which states is a protocol for MOM.. what does this mean?
MOM is about having a messaging middleware (middle layer) between (distributed) system components, and AMQP is protocol (set of rules) for reliably sending and receiving messages. So, a MOM implementation (i.e. Rabbitmq) may use AMQP.
What is MOM then?
Message-Oriented-Middleware - is an approach, an architecture for distributed system i.e. a middle layer for the whole distributed system, where there's lot of internal communication (a component is querying data, and then needs to send it to the other component, which will be doing some processing on the data) so components have to share info/data among them.
In short it's a way to design a system, for example: depending upon the overall requirements we need to develop a distributed system, with some internal communication. The biggest advantage of MOM architecture/decision is decoupling of the components i.e. if we're going to change the data query component it'll have no effect on the data processing components, as they're communicating via MOM (e.g. Rabbitmq Cluster) - the data processing component is getting the data in form messages, which then parses and processes them.
MOM at the end is just a design decision, that we use a middleware for gluing our system (distributed) components, a middleware for handling communication between them, in the form of messages (i.e. JSON). To implement a message-oriented-middleware we need more - set of specific rules i.e. how the messages will be published, consumed, how the acknowledgement will work, the lifetime of a message is until it is consumed, the persistence of a message, etc. AMQP is basically these set of rules i.e. a standard/protocol for implementing a MOM i.e. a messaging system using AMQP, means it confines itself by the stated rules. From Wikipedia:
AMQP mandates the behavior of the messaging provider and client to the
extent that implementations from different vendors are inter-operable,
in the same way as SMTP, HTTP, FTP, etc. have created inter-operable
systems.
I also have read that RabbitMQ implements the AMPQ protocol.. so why does that make a RabbitMQ a message broker?
Yes, Rabbitmq is a message broker (publisher -> exchange -> queue -> consumer). It's an open source AMQP implementation i.e. a messaging system/broker which confines to AMQP (the AMQP rules) - one can use Rabbitmq as the middleware, hence MOM.
AMQP - is just a set of rules i.e .how messages will be published, kept (in queues), consumed, delivery acknowledgement, etc.
Are a message broker and MOM the same thing?
In simple words, Yes. If we need to go with MOM design for our distributed system, we can simply use Rabbitmq (a message broker; an AMQP implementation) as the middleware.
"MOM" broadly means any technology that can deliver "messages" from one user-space application to another. A message is usually understood to be a discrete piece of information, as compared to a stream.
MOM products used to be quite large and complex: CORBA, JMS, TIBCO, WebsphereMQ, etc. and tried to do a lot more than simply deliver messages.
A broker is a particular set of routing and queuing patterns, and we usually use the term "broker" specifically in MOM (as compared to HTTP, email, XMPP, etc.) Routing means, one message goes to one peer, to one of many peers, to all of many peers, etc. Queuing means messages are held in memory or disk until they can be delivered (and in some cases, acknowledged).
AMQP used to specific those broker patters, so an application could rely on consistent behavior from any AMQP-compatible broker (thus RabbitMQ and OpenAMQ looked much the same to a client app, like two HTTP or two XMPP servers would look the same). AMQP/1.0 specifies just the connection between nodes, so you don't have guarantees of behavior. This makes AMQP/1.0 much easier for firms to implement, but doesn't deliver interoperability.
ZeroMQ is message-oriented middleware that defines, like AMQP/1.0, the connections between pieces rather than the behaviour of a central broker. However it's relatively easy to write MOM brokers using 0MQ, and we've done a few of these (like Majordomo).
Message brokers are one (quite popular) kind of MOM. Another kind of MOM would be brokerless MOM, like ZeroMQ. With broker based MOM, all messages go to one central place: broker, and get distributed from there. Broker less MOM usually allows for peer to peer messaging (but does not exclude option of central server as well) .
AMQP is broker based MOM protocol definition (at least all versions prior to 1.0, which drifts into more general MOM), and there are several different Message brokers implementing that protocol, RabbitMQ is just one of them.
On my team at work, we use the IBM MQ technology a lot for cross-application communication. I've seen lately on Hacker News and other places about other MQ technologies like RabbitMQ. I have a basic understanding of what it is (a commonly checked area to put and get messages), but what I want to know what exactly is it good at? How will I know where I want to use it and when? Why not just stick with more rudimentary forms of interprocess messaging?
All the explanations so far are accurate and to the point - but might be missing something: one of the main benefits of message queueing: resilience.
Imagine this: you need to communicate with two or three other systems. A common approach these days will be web services which is fine if you need an answers right away.
However: web services can be down and not available - what do you do then? Putting your message into a message queue (which has a component on your machine/server, too) typically will work in this scenario - your message just doesn't get delivered and thus processed right now - but it will later on, when the other side of the service comes back online.
So in many cases, using message queues to connect disparate systems is a more reliable, more robust way of sending messages back and forth. It doesn't work well for everything (if you want to know the current stock price for MSFT, putting that request into a queue might not be the best of ideas) - but in lots of cases, like putting an order into your supplier's message queue, it works really well and can help ease some of the reliability issues with other technologies.
MQ stands for messaging queue.
It's an abstraction layer that allows multiple processes (likely on different machines) to communicate via various models (e.g., point-to-point, publish subscribe, etc.). Depending on the implementation, it can be configured for things like guaranteed reliability, error reporting, security, discovery, performance, etc.
You can do all this manually with sockets, but it's very difficult.
For example: Suppose you want to processes to communicate, but one of them can die in the middle and later get reconnected. How would you ensure that interim messages were not lost? MQ solutions can do that for you.
Message queueuing systems are supposed to give you several bonuses. Among most important ones are monitoring and transactional behavior.
Transactional design is important if you want to be immune to failures, such as power failure. Imagine that you want to notify a bank system of ATM money withdrawal, and it has to be done exactly once per request, no matter what servers failed temporarily in the middle. MQ systems would allow you to coordinate transactions across multiple database, MQ and other systems.
Needless to say, such systems are very slow compared to named pipes, TCP or other non-transactional tools. If high performance is required, you would not allow your messages to be written thru disk. Instead, it will complicate your design - to achieve exotic reliable AND fast communication, which pushes the designer into really non-trivial tricks.
MQ systems normally allow users to watch the queue contents, write plugins, clear queus, etc.
MQ simply stands for Message Queue.
You would use one when you need to reliably send a inter-process/cross-platform/cross-application message that isn't time dependent.
The Message Queue receives the message, places it in the proper queue, and waits for the application to retrieve the message when ready.
reference: web services can be down and not available - what do you do then?
As an extension to that; what if your local network and your local pc is down as well?? While you wait for the system to recover the dependent deployed systems elsewhere waiting for that data needs to see an alternative data stream.
Otherwise, that might not be good enough 'real time' response for today's and very soon in the future Internet of Things (IOT) requirements.
if you want true parallel, non volatile storage of various FIFO streams(at least at some point along the signal chain) use an FPGA and FRAM memory. FRAM runs at clock speed and FPGA devices can be reprogrammed on the fly adding and taking away however many independent parallel data streams are needed(within established constraints of course).