The RabbitMQ module bundle provides an alternative way of publishing content and synchronizing instances in Magnolia. RabbitMQ is open source message broker software (a.k.a message-oriented middleware) that implements the Advanced Message Queuing Protocol (AMQP).
The Magnolia RabbitMQ modules are suitable for:
- Environments consisting of more than three public instances.
- Environments that need to synchronize with other environments.
The RabbitMQ alternative gives you full control over activation and synchronization, while reducing the load on your author environment. Activation is persisted into queues, allowing for easier setup of continuous deployment environments.
Maven is the easiest way to install the modules. Add the following dependencies to your bundle:
To get started even quicker consider using CloudAMQP to get RabbitMQ as a service.
RabbitMQ can be used for publication and/or synchronization. There exists a single exchange sever with multiple queues. RabbitMQ exchanges are configured in the connector module.
The exchange is configured on both author (producing instance) and public (consumer instance).
The connector module ships with a sample client configuration found here:
The value specified here must match the
Enables and disables the client. Toggling this property restarts the client.
Address of the broker.
Password of the user account to connect with.
Port number to connect the AMQP service.
Username of the user account to connect with.
Virtual host to connect to.
The exchange is the kind of router that the queues connect to. The producer instance pushes messages to the exchange and the exchange then decides what to do with them. You must configure the exchange configuration on the author or producing instance. An example exchange configuration is found with the sample client found here:
The name specified here must match the
Exchange type. See AMQP 0-9-1 Model Explained for more.
A list of queue definitions to bind with the exchange should be configured under the node
queueConfigList. A sample queue configuration can be found here:
Automatically deletes the queue when last consumer unsubscribes.
optional, default is
Used for only one connection. Queue is deleted when that connection closes.
Name of the queue.
Key used to route messages. The queue binds to the exchange with the routing key. Applicable when
Consuming messages on a public instance is called activation or publication. A sample consumer definition can be found here:
Used for monitoring. An ACK exchange is bound to a queue on which activation confirmation messages are sent.
Name of the client to use.
Consumer class which implements AbstractMQConsumerJob.
Enables and disables the consumer.
Name of the consumer.
Here are example to set up a producer and consumer using CloudAMPQ.
The producer (author) configuration is located here:
The consumer (public) configuration is located here:
You can confirm the connection(s) from the RabbitMQ console. When the(s) is enabled, the exchanges and queues should be visible. You can test this at
It's also possible to view the Queues and Exchanges from the console.
The RabbitMQ Activation module bootstraps activation commands into the standard Activation module. You can select commands/catalogs to match your purpose for using RabbitMQ.
The catalogs can be found here:
|Allows you to hook into transmission over RabbitMQ once you have done a standard activation.|
|Adds versioning to |
|Replaces standard activation with RabbitMQ versioned activation.|
The activate and deactivate commands defined in the above catalogs depend on your client and exchange configurations.
Configured client name.
Configured exchange name.
required , default is
When set to
required , default is
Stack size allows you to send more nodes per activation message, making messages bigger but reducing the number of messages in the queue.
optional , default is
Blocktime in seconds. Works only if
Blockactivation. Works only if
Minimum number of public instances to wait ack for. Works only if
Adding to apps
Using the RabbitMQ commands in your apps is simple. Reference the command to use by the catalog name.
Here is an example using the Pages app:
To test the new commands activate content and then open the RabbitMQ console. You should see messages in the queue (
Each activation is prefixed with a BOA (Beginning Of Activation) message and postfixed with a EOA (End Of Activation) message. When the consumer receives a message on a public instance, the message is stamped with the identity of the receiver and send back to the ack queue. When the author receives the message, the author knows exactly if the message started consuming the activation. In addition, identifying the activation in queue with BOA and EOA allow identification of TX inside the the queue.
Testing message consumption
When the activation consumer is configured, the receiving instance should start consuming messages.
Open the RabbitMQ console to verify that the specific queue (
fan1) is being emptied and that the nodes appear on the receiving instance.
While transactions are possible with RabbitMQ, they are complicated and slow down publishing. Ideally, the same activation message would be received by all instances at the same time, but this is technically very difficult to achieve and does not add much advantage in any event.
What is important however is that a Magnolia instance knows when a node is out of sync with another node, and that the load balancer knows which node is late. This is achieved by recording the time stamp and latest message state.
Whenever a message has been consumed and the content activated on the instance, the instance stores the message id (which is a
long that is incremented) and the date the message was activated.
This information is either sent to the load balancer or made available over a servlet. The goal is that the load balancer knows which instance is behind and by how much. In the example above the load balancer controlling tool knows that Public 1 and Public 2 are synced. It can decide to wait for Public 3 to sync, and if this does not happen, to alert the systems administrator or trigger the creation of a new instance.
SyncState and SyncStore mechanism
The Magnolia RabbitMQ implementation introduces the concepts of SyncState and SyncStore to achieve content synchronicity between public instances.
The mechanism is basically a counter that is incremented when each activation message is sent. The counter is sent in the message header. When the receiving instance gets the message, the instance increments its own activation counter. This means that two public instances which have different SyncStates are out of sync until the counters once again have the same number.
The load balancer calls the REST service of the public nodes and in this way knows which public node is most up to date and which one is out of sync.
|REST service is not responding.||Public node down.||Remove from the pool.|
|Rest service's sync state is 0.||Public Node is up but completely out of sync.|
|Public node is working but under heavy load.||Remove public node temporarily from the pool until |
The loadbalancer also knows when the public instances are getting activated. SyncStates are persisted to the JCR.
The Dynamically Weighted Least Connections Algorithm on your load balancer guarantees synchronicity and ensures that public instances do not get too far out of sync. See Least-Connection Algorithm based on variable weight for multimedia transmission for more.
The load balancer plays a big role in this. During a very big and long activation process, the load balancer can decide to redirect the traffic to the instances which have the highest and most equal ids. This increases traffic on these instances, which in turn slows down the activation process. Instances with initial low and unequal ids now have a higher chance of reaching the same state as the instances under load.
The algorithm creates a kind of "auto-damping" system that slows down instances by giving them more traffic, while speeding up the activation process on the others . Having the load balancer actively take the activation mechanism into consideration stabilizes the whole public node group.
- This module is at INCUBATOR level.