I know the HA Policy is set by the following command:
$ rabbitmqctl set_policy ha-all "" '{"ha-mode":"all","ha-sync-mode":"automatic"}'
My question which seems basic:
Do I have to issue this command on each node or just one of them?
RabbitMQ provides to distributes the policy to all the cluster, so it does not matter which node you select the info will be distribute to the other nodes.
Please read here: https://www.rabbitmq.com/clustering.html
A RabbitMQ broker is a logical grouping of one or several Erlang
nodes, each running the RabbitMQ application and sharing users,
virtual hosts, queues, exchanges, bindings, and runtime parameters.
Sometimes we refer to the collection of nodes as a cluster.
Related
About RabbitMQ two concept is unknow to me, cluster and node ? what is different between them?
A RabbitMQ node is the basic "message broker" service (process running on a server) which provides core RabbitMQ features such as exchanges, virtual hosts, queues, etc. You need at least one RabbitMQ node to be up-and-running, to use RabbitMQ.
A RabbitMQ cluster is simply a grouping of one or more RabbitMQ nodes. From the documentation, a cluster is:
"a logical grouping of one or several nodes, each sharing users, virtual hosts, queues, exchanges, bindings, runtime parameters and other distributed state.".
Why can it be useful to place nodes in a cluster? Again from the documentation:
Clustering nodes can help improve availability, data safety of queue contents and sustain more concurrent client connections.
So, a cluster of nodes gives you more flexibility (than a single node), about how you design and provide your overall RabbitMQ services.
The terms "node" and "cluster" are not specific to RabbitMQ - they are fairly generic terms, used much more widely than just for RabbitMQ.
I set up lab about ha for rabbitmq using cluster and mirror queue.
I am using centos 7 and rabbitmq-server 3.3.5. with three server (ha1, ha2, ha3).
I have just joined ha1 and ha2 to ha3, but do not set policy for mirror queue. When I test create queue with name "hello" on ha1 server, after i check on ha2, and ha3 using rabbitmqctl list queue, hello queue is exist on all node on cluster.
I have a question, why i do not set policy to mirror queue on cluster, but it automatic mirror queue have been created on any node on cluster?
Please give me advice about I have mistake or only join node on cluster, queue will be mirror on all node of cluster. Thanks
In rabbitmq , by default, one queue is stored only to one node. When you create a cluster, the queue is available across nodes.
But It does't mean that the queue is mirrored, if the node gets down the queue is marked as down and you can't access.
Suppose to create one queue to the node, the queue will work until the node is up, as:
if the node is down you will have:
you should always apply the mirror policy, otherwise you could lose the messages
We have setup a RabbitMQ cluster with 3 nodes. If an effort to have some form of load balancing, we setup the policy to only sync across 2 of the nodes:
rabbitmqctl set_policy ha-2 . '{"ha-mode":"exactly","ha-params":2,"ha-sync-mode":"automatic"}'
This works as expected when all 3 nodes are online.
When we shutdown one of the nodes (to simulate a failure) queues mastered on the failed node are still available (on the slave) but not synchronized to another node. If we manually re-apply the policy, the queues then synchronize as expected.
Should we expect that all queues be mirrored in the scenario that one node fails with this policy?
Works as expected in RabbitMQ 3.5.4
I would like to run RabbitMQ Highly Available Queues in a cluster of two RabbitMQ instances on two separate servers. It's not clear to me from the documentation how can I detect which node is considered as master by RabbitMQ in order to determine which node should I publish messages to and consume from.
Is that something that RabbitMQ resolves internally (and so I can publish and consume from master even when connected to a slave node) or should the application know about master node for each queue and connect only to it?
RabbitMQ will take care of that. The idea of HA queues is that you publish and consume from either node, and RabbitMQ will try to keep a consistent state.
I have a clustered HA rabbitmq setup. I am using the "exactly" policy similar to:
rabbitmqctl set_policy ha-two "^two\." \'{"ha-mode":"exactly","ha-params":10,"ha-sync-mode":"automatic"}'
I have 30 machines running, of which 10 are HA nodes with queues replicated. When my broker goes down (randomly assigned to be the first HA node), I need my celery workers to point to a new HA node (one of the 9 left). I have a script that automates this. The problem is: I do not know how to distinguish between a regular cluster node and a HA node. When I issue the command:
rabbitmqctl cluster_status
The categories I get are "running nodes", "disc", and "ram". but there is no way here to tell if a node is HA.
Any ideas?
In cluster every node share everything with another, so you don't have do distinguish nodes in your application in order to access all entities.
In your case when one of HA node goes down (their number get to 9), HA queues will be replicated to first available node (doesn't matter disc or ram).