http://activemq.apache.org/networks-of-brokers.html
I'm trying activemq network of brokers, following above article.
It works all fine with a fixed list of URIs.
But I have some problem with the multicast discovery. That is, the network bridge between two activemqs on the same machine can be started. But the bridge cannot establish between different machines(I tried telnet, it is ok).
I don't know which part went wrong. So I want to ask that is these two kind of network just difference in configuration?
Telnet is proving that Unicast networking is working, multicast may requires additional configuration in your network.
Are those machines in the same subnet?
Is there a router or Layer 3 switch between them? (it would then requires to be configured if the answer is yes..)
You could use iperf to test the multicast connectivity, you can look at Generating multicast traffic article to know how to do that.
Related
I can deliver normal UDP messages between two computers using a direct ethernet connection using my software. But I couldn't do the same for multicasting messages, I've tried other softwares that can send and receive multicast UDP messages and they didn't work as well. So I thought and wanted to ask if a direct Ethernet connection is a proper pyhsical setup or not. And if not what should I do?
Yes, a direct ethernet supports multicast. As opposed to an NBMA network like frame relay (rare these days) which does not support multicast for example.
Make sure you are not actually using a switch (which is a bridge) that has IGMP snooping enabled. IGMP snooping will not propagate multicast to nodes that have not sent an IGMP join (assuming your software does not do the join).
I'm newbie to DDS/Fast-RTPS.
Based on my understanding, the discovery is LAN-based. It failed to discover a node which is not in the same LAN. is it correct?
I'm wondering if we can use fast-rtps to communication across networks?
ps. let's ignore NAT/Firewall issues. Assuming we have a IP/TCP full reachable network environment.
DDS uses Multicast UDP. If your switches and other network infrastructure is set to swallow Multicast packets, or if the TTL is set too low, then the default discovery implementation of DDS will not complete/be seen.
You can up the TTL on your infrastructure, or you can tell the DDS libraries to target specific addresses (see the documentation for your provider's libraries).
I have setup the Rabbitmq cluster with two nodes deployed in two different machines.
I followed the steps in the link to make the communication across the nodes through SSL. I'm able to run through the steps without any issue.
Now that, I have completed the steps, how can I ensure that communication across cluster nodes is happening over SSL?
You have to capture packets in wireshark in the port you set for inter-node communication (by default it is 25672).
Then see in the wireshark capture if the protocol is SSL
I am starting to study ActiveMQ, and there is one question that I must have the answer as soon as possible: is it possible for a, say, console program, to know the IP of the machine where ActiveMQ is running without any previous information, like configuration file, or a parameter passed to the program? I wonder if ActiveMQ answers to some type of broadcast network message, reporting the IP of the computer it is running.
Thanks!
While your question is a bit vague on actual requirements and network capabilities etc, the most reasonable answer to this is to use discovery via multicast to locate a broker to connect to. There is documentation for this here, here, here and some here and more if you bother to search Google.
When you enable discovery on the broker's transport connector it will broadcast via multicast the IP address and port where a client can connect. You should do some research and even browse the ActiveMQ code to see how this works.
No, that's not possible. If all of the world's ActiveMQ servers were broadcasting their connection info to every producer or consumer in the world, that would be a ton of traffic. And if they were, how's a producer of consumer supposed to know which one to connect to, without being told? You have to tell the client how to reach the broker, and it's not a big deal to do.
It's unclear from the documentation why you should use Unicast rather than Multicast in a WebLogic cluster. Anyone have experience using either and the benefits of moving to Unicast?
The main difference between Unicast and Multicast is as follows
Unicast:
Say you have three servers (MS-1,MS-2,MS-3) in a cluster. If they have to communicate with each other, then they have to ping (i.e. heartbeats ) the cluster master for informing it that they are alive.
If MS-1 is the master then MS-2 and MS-3 would send the ping to MS-1
Multicast:
In Multicast, there is no cluster master. Instead each server has to ping each other to inform everyone that they are alive.
So MS-1 would send the ping to MS-2 & MS-3 and at the same time MS-2 would send the ping to MS-1 & MS-3 and MS-3 would ping MS-1 & MS-3.
Thus, in multicast there are more pings sent which makes the congestion in sending the pings much heavier compared to unicast. Because of this, WLS recommends using Unicast instead for less congestion in the network: Oracle Docs: Communications In a Cluster
The principle behind Multicast is that any message is received by all subscribers to the Multicast address. So MS-1 only needs to send 1 network packet to alert all other cluster members of its status. This means a status or JNDI update requires only 1 packet per Cluster for Muticast vs 1 packet per Server (approximately) for Unicast. Multicast also requires no "master" election. Multicast is thus far simpler to code and creates less network traffic.
So, Multicast is great? Not necessarily. It uses UDP datagrams which are inherently unreliable and un-acknowledged, so given the unreliable bearer protocol - Etherent - your message might never turn up (interpret: you fall out of the cluster). The whole concept of Multicast is based on subscription, it is not a 'routable' protocol in the normal sense, so by default routers must discard Multicast packets or risk a network storm. Hence the historical requirement for all cluster members to reside on the same network segment.
These shortcomings of Multicast mean Unicast is the way to go if your cluster spans networks or you're losing too many multicast packets.
The main benefit of Unicast over Multicast is ease of configuration. Unicast uses TCP communications and this usually requires no additional network configuration. Multicast uses UDP communication and Multicast addresses and this may require some network configuration and an additional effort in selecting the address to be used.
There is a great article from the Oracle A-Team with in-depth explanation: WebLogic Server Cluster Messaging Protocols.
In documentation for WLS 12.1.2 Oracle added Considerations for Choosing Unicast or Multicast in which they suggest to use Multicast in clusters with more than 10 Managed Servers.
In my personal experience I found that Unicast may give some problems in large clusters mainly because it is a new protocol introduced in WLS 10.0 and still suffer from some minor issues.
The answer here appears to conflict with the recommendation from the Oracle A-Team. Their recommendation is:
In general, the A-Team rule of thumb is to always recommend customers use multicast unless there is good reason why it isn’t possible or practical (e.g., spanning multiple subnets where routers are not allowed to propagate UDP multicast messages). The primary reasons for this are simply efficiency and resiliency to resource shortages.
The full article can be found here.
UPDATE
Weblogic defaults to unicast and documentation for 12c implies that multicast is only supported to ensure backward compatibility:
It is important to note that although parts of the WebLogic Server documentation suggest that multicast is only supported for backward compatibility—this is not correct. The multicast cluster messaging protocol is fully supported by Oracle. The A-team is working with WebLogic Server product management to address these documentation issues in the Weblogic Server 12c documentation.
Both multicast and unicast configurations have cluster masters. In addition to a cluster master, unicast has one or more leaders. The cluster leader may or may not be the cluster master.
Multicast is a broadcast; they do not ping each other like a tcp message. In both unicast and multicast cases, the traffic is usually trivial. But, multicast is almost always the best choice if you network supports it.
Unicast presents a simpler configuration than multicast in that you don't need multicast support. All routers/switches support TCP, but not all routers/switches support or have multicast enabled. But, unicast generates more network traffic than multicast.