Chapter 6. Network Connections: Acceptors and Connectors

There are two types of connections used in AMQ Broker: network and In-VM. Network connections are used when the two parties are located in different virtual machines, whether on the same server or physically remote. An In-VM connection is used when the client, whether an application or a server, resides within the same virtual machine as the broker.

Network connections rely on Netty. Netty is a high-performance, low-level network library that allows network connections to be configured in several different ways: using Java IO or NIO, TCP sockets, SSL/TLS, even tunneling over HTTP or HTTPS. Netty also allows for a single port to be used for all messaging protocols. A broker will automatically detect which protocol is being used and direct the incoming message to the appropriate handler for further processing.

The URI within a network connection’s configuration determines its type. For example, using vm in the URI will create an In-VM connection. In the example below, note that the URI of the acceptor starts with vm.

<acceptor name="in-vm-example">vm://0</acceptor>

Using tcp in the URI, alternatively, will create a network connection.

<acceptor name="network-example">tcp://localhost:61617</acceptor>

This chapter will first discuss the two configuration elements specific to network connections, Acceptors and Connectors. Next, configuration steps for TCP, HTTP, and SSL/TLS network connections, as well as In-VM connections, are explained.

6.1. About Acceptors

One of the most important concepts when discussing network connections in AMQ Broker is the acceptor. Acceptors define the way connections are made to the broker. Below is a typical configuration for an acceptor that might be in found inside the configuration file BROKER_INSTANCE_DIR/etc/broker.xml.

<acceptors>
   <acceptor name="example-acceptor">tcp://localhost:61617</acceptor>
</acceptors>

Note that each acceptor is grouped inside an acceptors element. There is no upper limit to the number of acceptors you can list per server.

Configuring an Acceptor

You configure an acceptor by appending key-value pairs to the query string of the URI defined for the acceptor. Use a semicolon (';') to separate multiple key-value pairs, as shown in the following example. It configures an acceptor for SSL/TLS by adding multiple key-value pairs at the end of the URI, starting with sslEnabled=true.

<acceptor name="example-acceptor">tcp://localhost:61617?sslEnabled=true;key-store-path=/path</acceptor>

For details on connector configuration parameters, see Acceptor and Connector Configuration Parameters.

6.2. About Connectors

Whereas acceptors define how a server accepts connections, a connector is used by clients to define how they can connect to a server.

Below is a typical connector as defined in the BROKER_INSTANCE_DIR/etc/broker.xml configuration file:

<connectors>
   <connector name="example-connector">tcp://localhost:61617</connector>
</connectors>

Note that connectors are defined inside a connectors element. There is no upper limit to the number of connectors per server.

Although connectors are used by clients, they are configured on the server just like acceptors. There are a couple of important reasons why:

  • A server itself can act as a client and therefore needs to know how to connect to other servers. For example, when one server is bridged to another or when a server takes part in a cluster.
  • A server is often used by JMS clients to look up connection factory instances. In these cases, JNDI needs to know details of the connection factories used to create client connections. The information is provided to the client when a JNDI lookup is performed. See Configuring a Connection on the Client Side for more information.

Configuring a Connector

Like acceptors, connectors have their configuration attached to the query string of their URI. Below is an example of a connector that has the tcpNoDelay parameter set to false, which turns off Nagle’s algorithm for this connection.

<connector name="example-connector">tcp://localhost:61616?tcpNoDelay=false</connector>

For details on connector configuration parameters, see Acceptor and Connector Configuration Parameters.

6.3. Configuring a TCP Connection

AMQ Broker uses Netty to provide basic, unencrypted, TCP-based connectivity that can be configured to use blocking Java IO or the newer, non-blocking Java NIO. Java NIO is preferred for better scalability with many concurrent connections. However, using the old IO can sometimes give you better latency than NIO when you are less worried about supporting many thousands of concurrent connections.

If you are running connections across an untrusted network, remember that a TCP network connection is unencrypted. You may want to consider using an SSL or HTTPS configuration to encrypt messages sent over this connection if encryption is a priority. Refer to Configuring Transport Layer Security for details.

When using a TCP connection, all connections are initiated from the client side. In other words, the server does not initiate any connections to the client, which works well with firewall policies that force connections to be initiated from one direction.

For TCP connections, the host and the port of the connector’s URI defines the address used for the connection.

Procedure

  1. Open the configuration file BROKER_INSTANCE_DIR/etc/broker.xml
  2. Add or modify the connection and include a URI that uses tcp as the protocol. Be sure to include both an IP or hostname as well as a port.

In the example below, an acceptor is configured as a TCP connection. A broker configured with this acceptor will accept clients making TCP connections to the IP 10.10.10.1 and port 61617.

<acceptors>
  <acceptor name="tcp-acceptor">tcp://10.10.10.1:61617</acceptor>
  ...
</acceptors>

You configure a connector to use TCP in much the same way.

<connectors>
  <connector name="tcp-connector">tcp://10.10.10.2:61617</connector>
  ...
</connectors>

The connector above would be referenced by a client, or even the broker itself, when making a TCP connection to the specified IP and port, 10.10.10.2:61617.

For details on available configuration parameters for TCP connections, see Acceptor and Connector Configuration Parameters. Most parameters can be used either with acceptors or connectors, but some only work with acceptors.

6.4. Configuring an HTTP Connection

HTTP connections tunnel packets over the HTTP protocol and are useful in scenarios where firewalls allow only HTTP traffic. With single port support, AMQ Broker will automatically detect if HTTP is being used, so configuring a network connection for HTTP is the same as configuring a connection for TCP. For a full working example showing how to use HTTP, see the http-transport example, located under INSTALL_DIR/examples/features/standard/.

Procedure

  1. Open the configuration file BROKER_INSTANCE_DIR/etc/broker.xml
  2. Add or modify the connection and include a URI that uses tcp as the protocol. Be sure to include both an IP or hostname as well as a port

In the example below, the broker will accept HTTP communications from clients connecting to port 80 at the IP address 10.10.10.1. Furthermore, the broker will automatically detect that the HTTP protocol is in use and will communicate with the client accordingly.

<acceptors>
  <acceptor name="http-acceptor">tcp://10.10.10.1:80</acceptor>
  ...
</acceptors>

Configuring a connector for HTTP is again the same as for TCP.

<connectors>
  <connector name="http-connector">tcp://10.10.10.2:80</connector>
  ...
</connectors>

Using the configuration in the example above, a broker will create an outbound HTTP connection to port 80 at the IP address 10.10.10.2.

An HTTP connection uses the same configuration parameters as TCP, but it also has some of its own. For details on HTTP-related and other configuration parameters, see Acceptor and Connector Configuration Parameters.

6.5. Configuring an SSL/TLS Connection

You can also configure connections to use SSL/TLS. Refer to Configuring Transport Layer Security for details.

6.6. Configuring an In-VM Connection

An In-VM connection can be used when multiple brokers are co-located in the same virtual machine, as part of a high availability solution for example. In-VM connections can also be used by local clients running in the same JVM as the server. For an in-VM connection, the authority part of the URI defines a unique server ID. In fact, no other part of the URI is needed.

Procedure

  1. Open the configuration file BROKER_INSTANCE_DIR/etc/broker.xml
  2. Add or modify the connection and include a URI that uses vm as the protocol.
<acceptors>
  <acceptor name="in-vm-acceptor">vm://0</acceptor>
  ...
</acceptors>

The example acceptor above tells the broker to accept connections from the server with an ID of 0. The other server must be running in the same virtual machine as the broker.

Configuring a connector as an in-vm connection follows the same syntax.

<connectors>
  <connector name="in-vm-connector">vm://0</connector>
  ...
</connectors>

The connector in the example above defines how clients establish an in-VM connection to the server with an ID of 0 that resides in the same virtual machine. The client can be be an application or broker.

6.7. Configuring a Connection from the Client Side

Connectors are also used indirectly in client applications. You can configure the JMS connection factory directly on the client side without having to define a connector on the server side:

Map<String, Object> connectionParams = new HashMap<String, Object>();

connectionParams.put(org.apache.activemq.artemis.core.remoting.impl.netty.TransportConstants.PORT_PROP_NAME, 61617);

TransportConfiguration transportConfiguration =
    new TransportConfiguration(
    "org.apache.activemq.artemis.core.remoting.impl.netty.NettyConnectorFactory", connectionParams);

ConnectionFactory connectionFactory = ActiveMQJMSClient.createConnectionFactoryWithoutHA(JMSFactoryType.CF, transportConfiguration);

Connection jmsConnection = connectionFactory.createConnection();