This question is a follow up to:
Akka Routing: Reply's send to router ends up as dead letters
I'm facing the same problem.
It is given in the answer that
"Note that different code would be needed if the routees were
not children of the router, i.e. if they were provided when the router was created."
I want to know What is that different code and how does it work? And is there any other way to communicate with the Router other than this method?
It'd be good if exlpained with code snippets or links to projects where it is used.
Related
I'm newbie in Apache Camel, so please forgive me for the stupid question.
I am browsing examples of sending messages using multicast and I don't understand it.
I know that (in the network layer) multicast source sends datagram to specified address from range 224.0.0.0 to 239.255.255.255, to subscribers, but multicast source "does not know" how many subscribers are, only one datagram is sent for anyone of subscribers .
I do not understand either the example from the documentation (https://camel.apache.org/components/latest/eips/multicast-eip.html#_multicast_example) or from here (https://www.javarticles.com/2015/05/apache-camel-multicast-examples.html).
Why (if I understood correctly) the subscribers of the message are explicitly specified ("direct: a", "direct: b", "direct: c")?
After all, in one moment there may be 3 of them, in another time 10 of them, and so on. I don't think I need to change the code and define e.g. "direct:10", am I right?
Does the Apache Camel multicast mean something different than the one from the network layer?
Yes its not the same. Multicast EIP is a way of sending a message to N recipients at the same time (where the number of recipient is fixed/known ahead of time).
yes, you correctly understand that there is difference between network layer multicast and apache camel multicast.
The use case for camel multicast is when you want to send same message to the multiple endpoints. So in example from docs:
from("direct:a").multicast().to("direct:x", "direct:y", "direct:z");
The same message from "direct:a" will be send to all three endpoints. And the number of "destination" endpoints is defined for each route and could be different for different routes.
Note that in case of:
from("direct:a").to("direct:x").to("direct:y")
You are chaining processing of the messages. The result from the "direct:a" will be send to "direct:x" and the result from "direct:x" will be send to "direct:y", so "direct:y" could get different message as "direct:x".
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I'd like to understand what exactly is the difference between the two Enterprise Integration Patterns
Content-Based Router
Message Router
The definition at camel documentation is suggestive that Content-Based router is a special case of Message Router. They why list them separately?
Actually "Message Router" is one of the "Basic Messaging Concepts". List of such basic messaging concepts is:
Channel - Messaging applications transmit data through a Message Channel, a virtual pipe that connects a sender to a receiver.
Message - A Message is an atomic packet of data that can be transmitted on a channel.
Multi-step delivery - Set of actions often need to be performed on the message after it is sent by its original sender but before it is received by its final receiver.
Routing - In a large enterprise with numerous applications and channels to connect them, a message may have to go through several channels to reach its final destination. The route a message must follow may be so complex that the original sender does not know what channel will get the message to the final receiver. Instead, the original sender sends the message to a Message Router.
Transformation - Various applications may not agree on the format for the same conceptual data; the sender formats the message one way, yet the receiver expects it to be formatted another way.
Endpoint - An application does not have some built-in capability to interface with a messaging system. Rather, it must contain a layer of code that knows both how the application works and how the messaging system works, bridging the two so that they work together.
"Content Based Router" is one of the "Message Routers" and there are a lot of different other Message Routers available like "Message Filter", "Splitter", "Aggregator", "Recipient list" etc.
I suggest reading a book that used by camel so all such points will be more clear:
https://www.amazon.com/o/asin/0321200683/ref=nosim/enterpriseint-20
As far as I understand the patterns Message Router only applies when the input and output is a queue or topic of a messaging system.
Content-based Router is not limited to messaging. I think you can say that inside a Message Router you have a Content-based router that decides which way to go.
In camel the decision is made using the choice() element.
If my assumption is correct then the documentation of the Message-Router at camel is wrong as it does not reflect the queues. I will check with the camel dev list and correct the wiki page if we agree on this.
There are quite a couple of related questions (e.g. Java Socket specify a certain network interface for outgoing connections ) however I couldn't find a satisfying i.e. practical solution to my problem:
On my target (Linux) platform there are multiple network interfaces (eth0...ethN) from which a Server S is reachable. The default route is normally via eth0, however I'm trying to connect S via e.g. eth4 using
new java.net.Socket(IP_of_S, targetport, IP_of_eth4, srcport)
or
sock.bind( eth4_SocketAddress );
sock.connect( S_SocketAddress );
In this example case the IP of eth4 is assigned correctly but traffic is still going out trough the interface of the default route. I've learned this is due to the the "weak end system model" RFC 1122. However I'm wondering whether there's still a Java-based solution to achieving my original goal or whether I have to trigger external iptables or route calls from my program.
(BTW: The outgoing interface needs to be chosen dynamically at runtime, i.e. my program closes the connection and tries to reconnect using a different outbound interface quite frequently.)
As far as I know, you cannot choose the outgoing interface without some routing table setup.
In my opinion, the best solution is to set up a bunch of source-specific routes, routes that match on the source address of a packet, and bind to a given source address in order to select the route (as you already do). There are two ways of achieving that:
use ip rule and multiple routing tables — this is described in http://lartc.org/howto/lartc.rpdb.html ;
use ip route add ... from .... As far as I know, this only works for IPv6, but avoids the complexity of multiple routing tables.
You'll find some background about source-specific routing in https://arxiv.org/pdf/1403.0445v4.pdf (disclaimer, I'm a co-author).
so I have been following this tutorial: http://www.rabbitmq.com/tutorials/tutorial-six-java.html, but I cant get it to work with a direct exchange.
Can someone help me out please by modifying the code so that it works with a direct exchange.
My objective: the user can chose which machine to send to, When they choose i want to bind to that machine and just send it to that machine. But it doesn't seem to be working when i change the queue declare to exchange declare. Any help would be greatly appriciated!!!
Thanks
In RabbitMQ you publish messages to exchanges, so the code you are seeing in the tutorial: channel.basicPublish("", "rpc_queue", props, message.getBytes());, means: send a message to the exchange "", using routing key "rpc_queue". That's the default or anon exchange discussed in tutorial one.
So if you want to send a message to a direct exchange, just change the empty exchange name for your exchange name.
Now, why do you want to do it that way? Why can't you instead of declaring an "rpc_queue", you declare a queue per machine, and address them by their names, in basicPublish?
I'm writing an application server that will receive SIP and DNS messages from the network.
When I receive a message from the network, I understand from the documentation that at first, I get a ChannelBuffer. I would like to determine which kind of message has been received (SIP or DNS) and to decode it.
To determine the message type, I can dedicate port to each type of message, but I would be interested to know if there exist another solution for that. My question is more about how to decode the ChannelBuffer.
Is there a ChannelHandler provided by Netty to decode SIP or DNS messages? If not, what would be the right place in the type hierarchy to write my custom ChannelHandler?
To illustrate my question, let's take as example the HttpRequestDecoder, the hierarchy is:
java.lang.Object
org.jboss.netty.channel.SimpleChannelUpstreamHandler
org.jboss.netty.handler.codec.frame.FrameDecoder
org.jboss.netty.handler.codec.replay.ReplayingDecoder<HttpMessageDecoder.State>
org.jboss.netty.handler.codec.http.HttpMessageDecoder
org.jboss.netty.handler.codec.http.HttpRequestDecoder
Also, do I need to use two different ChannelHandler for decoding and encoding, or is there a possibility to use a single ChannelHandler for both?
Thanks
If you really have a requirement for port unification (an example here), i.e. receiving different protocols on the same port, then you would have to detect the protocol in a handler and take appropriate actions. Could be as simple as inserting different handlers in the pipe line.
However, I find it very improbable that SIP and DNS would share the same port, hence no need to complicate matters.
I haven't seen a SIP decoder/encoder for Netty, but depending on what you want to do with the message, the HTTP decoder is a a very good starting point (and could be made simpler since chunking is not supported in SIP).
I would strongly recommend not to try to combine DNS and SIP decoding in one handler (or any other combination for that matter). Keep the handlers as simple and coherent as possible. Combine handlers instead, if needed.