I have a curiosity and I was searching for it without any result. In GlassFish documentation it is written:
If the GlassFish Server instance on which the application client is
deployed participates in a cluster, the GlassFish Server finds all
currently active IIOP endpoints in the cluster automatically. However,
a client should have at least two endpoints specified for
bootstrapping purposes, in case one of the endpoints has failed.
but I am asking myself how this list is created.
I've done some tests with a stand-alone client that is executed in a JVM and does some RMI calls on an application that is deployed in a GlassFish cluster and I can see from the logs that the IIOP endpoints list is completed automatically and it is set as com.sun.appserv.iiop.endpoints system property but if I stop a server instance or start another during the execution of the client the list remains the one that was created when the JVM was started.
GlassFish clustering is managed by the GMS (Group Management Service) which usually uses UDP Multicast, but can use TCP where that is not available.
See section 4 "Administering GlassFish Server Clusters" in the HA Administration Guide (PDF)
The Group Management Service (GMS) enables instances to participate in a cluster by
detecting changes in cluster membership and notifying instances of the changes. To
ensure that GMS can detect changes in cluster membership, a cluster's GMS settings
must be configured correctly.
Related
I have a weblogic cluster which has 4 nodes (managed servers). Today I found two of them are down, and I found in suprise that some JMS messages are not sent.
I wonder if it's the normal behaviour ? Shouldn't the cluster continue to deliver JMS using the two available nodes ?
In order to reach high availability for JMS you should configure two things
Migratable targets.
Persistance based either on shared storage or a database.
Why migratable targets? This is because messages produced by i.e. JMSServer01 can only be processed by JMSServer01. Thus, when you configure migratable targets the JMSServer01 will be migrated automatically into another Weblogic server.
Why persistance based on shared storage or a database? This is because once the JMS Server is migrated into another server, it will try to process the messages, which must be in a shared storage or database that can be seen by all your Weblogic servers.
You can find more information here https://docs.oracle.com/middleware/1213/core/ASHIA/jmsjta.htm#ASHIA4396
I am trying to setup a distributed system based on current spring-cloud release (meaning mostly Netflix OSS) using the following components
1 or more cloud config servers
1 or more Eureka servers
1 or more services using Eureka and Config Server clients
The setup above is easy enough to get going however once you start looking into setting up so that configuration changes in the cloud Config servers automatically trigger changes in the values of the actual clients, things start getting more complicated.
It is my understanding that for such a feature to work one should introduce spring-cloud-bus clients to the services which in turn will use, currently the only supported implementation, rabbitmq servers (the actual rabbitmq binaries and not some spring-boot app like eureka or Config servers) to allow change events in the Config server to be propagated to the clients automatically.
It sounds counterintuitive to setup such a system and have to hardcode addresses to rabbitmq servers in the clients (even if one will be keeping the amount of rabbitmq servers more or less static).
How is one supposed to register rabbitmq server instances in the Eureka service discovery server(s) to allow for clients to find them without having to have any knowledge about their location prior to startup?
I cannot seem to find any documentation on how this is done given that rabbitmq is not a spring-cloud component. In fact very little documentation seems to exist regarding on how the rabbitmq + eureka + spring-cloud-bus should be setup together.
I know that I am on a VERY old question, even though I think it worth a comment for people who read this in the future.
Most of the cloud services, lets take AWS as an example, have an Elastic IP solution - so you can configure IPs for RabbitMQ servers, and the IPs always belong to the RabbitMQ, no matter whether the instances change. You can re-attach the Elastic IP to different instances.
It works nearly the same with Elastic Load Balancer, which keeps its IP, so you could configure your microservices to a specific IP using Spring Cloud Config Server - and scale the RabbitMQ instances without a need to worry about configuration change.
Currently we have 2 load balanced web servers. We are just starting to expose some functionality over NSB. If I create two "app" servers would I create a cluster between all 4 servers? Or should I create 2 clusters?
i.e.
Cluster1: Web Server A, App Server A
Cluster2: Web Server B, App Server B
Seems like if it is one cluster, how do I keep a published message from being handled by the same logical subscriber more than once if that subscriber is deployed to both app server A and B?
Is the only reason I would put RabbitMQ on the web servers for message durability (assuming I didn't have any of the app services running on the web server as well)? In that case my assumption is that I am then using the cluster mirroring to get the message to the app server. Is this correct?
Endpoints vs Servers
NServiceBus uses the concept of endpoints. An endpoint is related to a queue on which it receives messages. If this endpoint is scaled out for either high availability or performance then you still have one queue (with RabbitMQ). So if you would have an instance running on server A and B they both (with RabbitMQ) get their messages from the same queue.
I wouldn't think in app servers but think in endpoints and their non functional requirements in regards to deployment, availability and performance.
Availability vs Performance vs Deployment
It is not required to host all endpoints on server A and B. You can also run service X and Y on server A and services U and V on server B. You then scale out for performance but not for availability but availability is already less of an issue because of the async nature of messaging. This can make deployment easier.
Pubsub vs Request Response
If the same logical endpoint has multiple instances deployed then it should not matter which instance processes an event. If it is then it probably isn't pub sub but async request / response. This is handled by NServiceBus by creating a queue for each instance (with RabbitMQ) on where the response can be received if that response requires affinity to requesting instance.
Topology
You have:
Load balanced web farm cluster
Load balanced RabbitMQ cluster
NServiceBus Endpoints
High available multiple instances on different machines
Spreading endpoints on various machines ( could even be a machine per endpoint)
A combination of both
Infrastructure
You could choose to run the RabbitMQ cluster on the same infrastructure as your web farm or do it separate. It depends on your requirements and available resources. If the web farm and rabbit cluster are separate then you can more easily scale out independently.
I have a JMS service targeted at a migratable target (using an Auto-Migrate Exactly-Once policy) in a cluster which consists of 2 managed servers, at any point of time the service is hosted at one of them and the consumer (which is targeted at the cluster) is supposed to receive messages seamlessly no matter where the service is hosted.
When I manually switch the host of the migratable target (clicking migrate), without turning the hosting managed server off, the consumer fails to receive messages sent to the queues, unless I turn off the previous hosting managed server forcing the consumer to the new host.
I can rule out sender problems, I can see the messages in the queue right after them being sent.
I'll be grateful if anyone can advice on how to configure either the consumer or the migratable service to work seamlessly when migration happens.
I think that may just be a misunderstanding of how migration works. The docs state Auto-Migrate Exactly-Once:
indicates that if at least one Managed Server in the candidate list
is running, then the JMS service will be active somewhere in the
cluster if servers should fail or are shut down (either gracefully or
forcibly). For example, a migratable target hosting a path service
should use this option so if its hosting server fails or is shut down,
the path service will automatically migrate to another server and so
will always be active in the cluster. Note that this value can lead to
target grouping. For example, if you have five exactly-once migratable
targets and only one server member is started, then all five
migratable targets will be activated on that server member.
The docs also state:
Manual Service Migration—the manual migration of pinned JTA and
JMS-related services (for example, JMS server, SAF agent, path
service, and custom store) after the host server instance fails
Your server/service has neither failed or shut down, you are forcing it to migrate with a healthy host still running, so it has not met the criteria for migration.
See more here as well.
I have some experience that sounds reminiscent of what you're looking at. There was some WLS-specific capability around recognizing reconfiguration in JMS destinations as part of their clustered server design.
In one case I had to call a WLS-specific method: weblogic.jms.extensions.WLSession.setExceptionListener(). This was on their implementation of the JMS Session interface. This is analogous to the standard JMS Connection.setExceptionListener().
With this WLS-specific capability, the WLSession.setExceptionListener() callback would occur at a point where the consuming client should tear down and re-establish the connection / session / consumer in reaction to a reconfiguration (migration) that had happened.
I have a WebLogic cluster on which I've deployed numerous topics and applications that use them. My applications uniformly show themselves in a Warning status. Looking at Monitoring on the deployment, I see the MDB application connects to Server #1, but on server #2 it shows this:
MDB application appName is NOT connected to messaging system.
My JMS Server is targetted to a migratable target, which is in turn targetted to the #1 server and has a cluster identified. And messages sent to either server all flow as expected. I just don't know why these deployments show in a Warning state.
WebLogic 11g
This can be avoided by using the parameter below
<start-mdbs-with-application>false</start-mdbs-with-application>
In the weblogic-application.xml, Setting start-mdbs-with-application to false forces MDBs to defer starting until after the server instance opens its listen port, near the end of the server boot up process.
If you want to perform startup tasks after JMS and JDBC services are available, but before applications and modules have been activated, you can select the Run Before Application Deployments option in the Administration Console (or set the StartupClassMBean’s LoadBeforeAppActivation attribute to “true”).
If you want to perform startup tasks before JMS and JDBC services are available, you can select the Run Before Application Activations option in the Administration Console (or set the StartupClassMBean’s LoadBeforeAppDeployments attribute to “true”).
Refer :http://docs.oracle.com/cd/E13222_01/wls/docs81/ejb/message_beans.html
this is applicable for the versions till 12c and later
I don't like unanswered questions, so I'm going to answer this one.
The problem is resolved, though I was not involved in its resolution. At present the problem only exists for the length of time it takes the JMS subsystem to fully initialize. During that period (with many queues, it can take a while) the JNDI system throws errors and the apps are truly in warning state. Once the JMS is fully initialized, everything goes green.
My belief is that someone corrected something in the JMS Server / Cluster config. I'll never know what it was.