Let's say I initialize Curator giving it a single Zookeeper server to CuratorFrameworkFactory#newClient. Will Apache Curator automagically discover the other servers in the ensemble? Or will I always need to specify all servers in the connection string for it to gracefully switch over to other leader when/if that happens?
Related
I've started exploring Redis Cluster and it's C client(hiredis). I've been unable to find much info about the client's interaction with the Redis cluster. I've got some queries in this regard:
Does the client make a connection with all the nodes of the cluster(master and slaves) in the beginning?
Is there any coordinator node which proxies the client's request to the correct node?
If not, does the client periodically get the info about the hash-slot holdings of each node in the cluster(in order to send its request to the correct node)?
Which client-cluster connection specific parameters are configurable?
Does the client make a connection with all the nodes?
Yes, the client maintains a connection with all the masters at least.
Is there a coordinator node which proxies the client's request to the correct node?
No, there isn't. By design, redis cluster does not have a proxy.
(Aside: There is some talk of developing a proxy solution for redis - but I don't expect it to be released any time soon.)
Does the client periodically get info about hash slot bindings?
When a client starts up, it builds up a cache of hash-slot mappings. Then, at runtime, if a slot is migrated to another master, redis cluster will return a specific error that will tell the client the new owner for that slot. The client is then expected to cache the new owner, and retry the request against the new node.
As a result of this design, clients usually have a very good cache of every slot and it's owner, and there is very little overhead.
which client connection parameters are configurable?
The most important parameter is the list of server nodes to connect to the cluster. You don't have to specify all the nodes - the client can auto-discover all the masters. As long as even one node is active, the client will discover all the other nodes.
Apart from that, you have connection timeout parameters, parameters to control TLS.
We are trying to prevent our application startups from just spinning if we cannot reach the remote cluster. From what I've read Force Server Mode states
In this case, discovery will happen as if all the nodes in topology
were server nodes.
What i want to know is:
Does this client then permanently act as a server which would run computes and store caching data?
If connection to the cluster does not happen at first, a later connection to an establish cluster cause issue with consistency? What would be the expect behavior with a Topology version mismatch? Id their potential for a split brain scenario?
No, it's still a client node, but behaves as a server on discovery protocol level. For example, it can start without any server nodes running.
Client node can never cause data inconsistency as it never stores the data. This does not depend forceServerMode flag.
i have the following scenario which i want to fulfill:
rabbit mq must be loadbalanced (is it something which is provided by rabbitmq out of the box OR something like haproxy load balancer would work great. Which one is well loadbalanced.)
CAN haproxy directly push messages to rabbitmq (lets say a POST request coming to http://localhost:3333/redirectToRabbit gets redirected to rabbit and optionally either the ACK or RESPONSE goes back to client. Also note haproxy would load balance the request)
with HA; what the best configuration ( exchange with durable queue, durable queue or something else. NOTE: How would the messages gets redirected to some other rabbitmq instance if one of the rabbitmq instance goes down -- persisted and auto redirection to available rabbitmq )
Assuming you setup a two-node RabbitMQ cluster. Before talking about ha proxy, you need to understand the ha policies and the behavior of ha queues first. Different ha options might cause completely different behaviors of RabbitMQ message replication and node failover. RabbitMQ is so flexible, so don't expect a golden way of configuration which could meet all scenarios.
Then, since you have two nodes which could accept connections, your client could either use a loadbalancer (such as ha proxy) or to use a client driver which supports connecting to multiple nodes of a cluster. Either way will work.
When using haproxy, you have one load balancer ip. Client connects only to this load balancer ip, the load balancer forward you connection to the underlying nodes. But as long as a connection created, the client connection instance keeps talking to one of the node. When one of the node is down, if no "Health Checking" options are configured in your load balancer, client might get random connection failures. When you have "Health Checking" options configured correctly, the load balancer knows which nodes are down, so that clients will only connect to healthy nodes, which solves the issue.
When not using a load balancer and only base on client driver to connect to all the nodes, the client driver should be able to handle connection failure or health check internally and do failover/retry, etc, to ensure connections go to healthy nodes.
I'm trying to configure master/slave configuration using apache zookeeper. I have 2 application servers only on which I'am running activemq. as per the tutorial given at
[1]: http://activemq.apache.org/replicated-leveldb-store.html we should have atleast 3 zookeeper servers running. since I have only 2 machines , can I run 2 zookeeper servers on 1 machine and remaining one on another ? also can I run just 2 zookeeper servers and 2 activemq servers respectively on my 2 machines ?
I will answer the zookeper parts of the question.
You can run two zookeeper nodes on a single server by specifying different port numbers. You can find more details at http://zookeeper.apache.org/doc/r3.2.2/zookeeperStarted.html under Running Replicated ZooKeeper header.
Remember to use this for testing purposes only, as running two zookeeper nodes on the same server does not help in failure scenarios.
You can have just 2 zookeeper nodes in an ensemble. This is not recommended as it is less fault tolerant. In this case, failure of one zookeeper node makes the zookeeper cluster unavailable since more than half of the nodes in the ensemble should be alive to service requests.
If you want just POC ActiveMQ, one zookeeper server is enough :
zkAddress="192.168.1.xxx:2181"
You need at least 3 AMQ serveur to valid your HA configuration. Yes, you can create 2 AMQ instances on the same node : http://activemq.apache.org/unix-shell-script.html
bin/activemq create /path/to/brokers/mybroker
Note : don't forget du change port number in activemq.xml and jetty.xml files
Note : when stopping one broker I notice that all stopping.
Glassfish 3.1.2
Ubuntu 12.04
I've created a cluster of two nodes and have a JMS queue.
I'm having issues trying to connect to this JMS queue using a remote standalone client.
The cluster JMS listener is on port 27676 and the queue is deployed to the cluster.
mq://Glassfish2:27676/,mq://Glassfish3:27676
When I connect using the code I'd use to connect to a stand alone instance the message is not received by the cluster.
I believe it is using the default 7676 port. When the IIOP port is changed to use port 23700 which is the one the cluster (DAS) is using I get a connection refused exception as it is trying to connect to localhost:27676. At least it's the right port.
WARNING: [C4003]: Error occurred on connection creation [localhost:27676]. - cause: java.net.ConnectException: Connection refused: connect
I've also updated the following values in node config file (domain.xml) to remove references to localhost. jms-host and node-host values.
I had this issue before with a stand alone instance and it was resolved by adding entries to the /etc/hosts file. However, this does not seem to resolve the issue.
I also have all server instance IPs in the hosts file.
Am I missing something very basic here?
Any help would be greatly appreciated.
Thanks
If you look log files under
${glassfish_home}/glassfish/nodes/cluster-name/instance-name/imq/instances/instance-name/log
folder, you will see that
master brockers does not match
Every your node has different master brockers, probably every node know its own brocker as master brocker..
I had the same error and after a few days find this..