public static void main(String[] args) throws Exception {
 MQTT mqtt = new MQTT(); mqtt.setHost("localhost", 1883); 
// mqtt.setUserName(user); 
// mqtt.setPassword(password);
 FutureConnection connection = mqtt.futureConnection(); 
connection.connect().await();
 UTF8Buffer topic = new UTF8Buffer("foo/blah/bar"); 
Buffer msg = new AsciiBuffer("mqtt message"); 
Future<?> f = connection.publish(topic, msg, QoS.AT_LEAST_ONCE, false);
 f.await(); 
connection.disconnect().await(); 
System.exit(0); 
}

Server

AUTO

security

https://activemq.apache.org/security

authentication

Simple authentication

stay activemq.xml of broker Simple authentication plug-ins and users are configured in the configuration file

<plugins>
 <!-- Configure authentication; Username, passwords and groups -->         
     <simpleAuthenticationPlugin> 
            <users> 
                <authenticationUser username="system" password="manager" groups="users,admins"/> 
                <authenticationUser username="user" password="password" groups="users"/>        
                 <authenticationUser username="guest" password="password" groups="guests"/>     
            </users> 
     </simpleAuthenticationPlugin> 
</plugins>

ConnectionFactory connectionFactory = new ActiveMQConnectionFactory(username,password,url);

Support anonymous access

<simpleAuthenticationPlugin anonymousAccessAllowed="true">.....

JAAS mode

 

• Configure the JAAS plug-in in the broker of activemq.xml.

<plugins> 
<!--use JAAS to authenticate using the login.config file on the classpath to configure JAAS --> 
<jaasAuthenticationPlugin configuration="activemq" />
 </plugins>

confifiguration="activemq" Specify use login.confifig Medium "activemq" to configure.

conf/login.confifig

activemq { 
  org.apache.activemq.jaas.PropertiesLoginModule required 
  org.apache.activemq.jaas.properties.user="users.properties" 
  org.apache.activemq.jaas.properties.group="groups.properties"; 
};

• Configure users in conf/users.properties   

#User name = password
 admin=admin
 user=password 
guest=guest

• Configure user groups (roles) in conf/groups.properties

#Group name = user 1, user 2 group name custom 
admins=admin 
users=admin,user 
guests=guest

Permission control

Control user group pair Queue/Topic Operation permissions.

Permissions include: read only   Write only and admin

You can add any of these in the configuration

 

  ActiveMQ high availability cluster

Master Slave

Master-slave scheme   High availability cluster

https://activemq.apache.org/masterslave

  ActiveMQ provides a master-slave cluster mechanism to achieve high availability.   

The master and slave are selected through distributed locks. There is a common data implementation, and the intermediate data cannot be killed

• Multiple Broker instances share storage
• Multiple brokers become masters by grabbing exclusive locks
• The Master node provides external services, and the Slave node suspends waiting for the exclusive lock
• If the Master node fails, non persistent messages will be lost, so persistent messages are generally used.
• Clients connect in a multi Broker failover mode

failover:(tcp://broker1:61616,tcp://broker2:61616,tcp://broker3:61616)

Broke1 restart

• The Shared File System Master Slave exclusive lock is the lock file in the shared storage directory

• The JDBC Master Slave exclusive lock is activemq_lock table record

As mentioned earlier, there is a lock under the KahaDB directory in the log record. This lock is implemented by the distributed lock.

In a large number of high concurrency scenarios, this cluster still can't work. No load balancing. Not suitable.

  Distributed queues and topics

Distributed queue   And topics use this method to solve the problem of high concurrency  

Starting with 1.1, ActiveMQ supports proxy networks, which enables us to support distributed queues and topics across proxy networks. This allows the client to connect to any agent in the network and fail over to another agent if necessary. There is a failure - provide an HA agent cluster from the client's point of view

• Independent brokers are connected to each other;
• The client uses Failover to connect to any Broker;
• The message produced by the client is sent to the broker to which it is connected and stored on the broker;
• The consumer client can connect to any Broker to consume the messages of the target.

Distributed queues in store / forward

When we publish A message on the queue, it is stored in the publisher that is communicating. Then, if the agent is configured to store / forward to other agents, for clients, the agent will send it to one of these clients (which can be A node or agent), depending on the scheduling algorithm). This dispatch algorithm will continue until the message is deleted and finally sent and used by the client. At any point in time, messages will only exist in the storage of one agent before they are consumed. Note that messages are distributed to other agents only if there are consumers on them. e. g. if there are agents A, B, C and publishers in the queue on A. If there are consumers in the queue on A and B, the messages in the queue will be distributed on agents A and B; Some messages will be sent to B, some messages will be used on A, and no messages will be sent to C. If there are consumers in the queue, start with C, and then the message will flow there. If the consumer stops, no more messages are sent to C.