In this chapter we’ll describe the concepts required for understanding Apache ActiveMQ Artemis transports and where and how they’re configured.

1. Acceptors

One of the most important concepts in Apache ActiveMQ Artemis transports is the acceptor. Let’s dive straight in and take a look at an acceptor defined in xml in the configuration file broker.xml.

<acceptor name="netty">tcp://localhost:61617</acceptor>

Acceptors are always defined inside an acceptors element. There can be one or more acceptors defined in the acceptors element. There’s no upper limit to the number of acceptors per server.

Each acceptor defines a way in which connections can be made to the Apache ActiveMQ Artemis server.

In the above example we’re defining an acceptor that uses Netty to listen for connections at port 61617.

The acceptor element contains a URL that defines the kind of Acceptor to create along with its configuration. The schema part of the URL defines the Acceptor type which can either be tcp or vm which is Netty or an In VM Acceptor respectively. For Netty the host and the port of the URL define what host and port the acceptor will bind to. For In VM the Authority part of the URL defines a unique server id.

The acceptor can also be configured with a set of key=value pairs used to configure the specific transport, the set of valid key=value pairs depends on the specific transport be used and are passed straight through to the underlying transport. These are set on the URL as part of the query, like so:

<acceptor name="netty">tcp://localhost:61617?sslEnabled=true;keyStorePath=/path</acceptor>

2. Connectors

Whereas acceptors are used on the server to define how we accept connections, connectors are used to define how to connect to a server.

Let’s look at a connector defined in our broker.xml file:

<connector name="netty">tcp://localhost:61617</connector>

Connectors can be defined inside a connectors element. There can be one or more connectors defined in the connectors element. There’s no upper limit to the number of connectors per server.

A connector is used when the server acts as a client itself, e.g.:

• When one server is bridged to another

• When a server takes part in a cluster

In these cases the server needs to know how to connect to other servers. That’s defined by connectors.

3. Configuring the Transport Directly from the Client

How do we configure a core ClientSessionFactory with the information that it needs to connect with a server?

Connectors are also used indirectly when configuring a core ClientSessionFactory to directly talk to a server. Although in this case there’s no need to define such a connector in the server side configuration, instead we just specify the appropriate URI.

Here’s an example of creating a ClientSessionFactory which will connect directly to the acceptor we defined earlier in this chapter, it uses the standard Netty TCP transport and will try and connect on port 61617 to localhost (default):

ServerLocator locator = ActiveMQClient.createServerLocator("tcp://localhost:61617");
ClientSessionFactory sessionFactory = locator.createClientSessionFactory();
ClientSession session = sessionFactory.createSession(...);

Similarly, if you’re using JMS, you can configure the JMS connection factory directly on the client side:

ConnectionFactory connectionFactory = new ActiveMQConnectionFactory("tcp://localhost:61617");
Connection jmsConnection = connectionFactory.createConnection();

4. Configuring the Netty transport

Out of the box, Apache ActiveMQ Artemis currently uses Netty, a high performance low level network library.

Our Netty transport can be configured in several different ways; to use straightforward TCP sockets, SSL, or to tunnel over HTTP or HTTPS..

We believe this caters for the vast majority of transport requirements.

4.1. Single Port Support

Apache ActiveMQ Artemis supports using a single port for all protocols, Apache ActiveMQ Artemis will automatically detect which protocol is being used CORE, AMQP, STOMP, MQTT or OPENWIRE and use the appropriate Apache ActiveMQ Artemis handler. It will also detect whether protocols such as HTTP or Web Sockets are being used and also use the appropriate decoders. Web Sockets are supported for AMQP, STOMP, and MQTT.

It is possible to limit which protocols are supported by using the protocols parameter on the Acceptor like so:

<acceptor name="netty">tcp://localhost:61617?protocols=CORE,AMQP</acceptor>

4.2. Configuring Netty TCP

Netty TCP is a simple unencrypted TCP sockets based transport. If you’re running connections across an untrusted network please bear in mind this transport is unencrypted. You may want to look at the SSL or HTTPS configurations.

With the Netty TCP transport all connections are initiated from the client side (i.e. the server does not initiate any connections to the client). This works well with firewall policies that typically only allow connections to be initiated in one direction.

All the valid keys for the tcp URL scheme used for Netty are defined in the class org.apache.activemq.artemis.core.remoting.impl.netty.TransportConstants. Most parameters can be used either with acceptors or connectors, some only work with acceptors. The following parameters can be used to configure Netty for simple TCP:

host

This specifies the host name or IP address to connect to (when configuring a connector) or to listen on (when configuring an acceptor). The default value for this property is localhost. When configuring acceptors, multiple hosts or IP addresses can be specified by separating them with commas. It is also possible to specify 0.0.0.0 to accept connection from all the host’s network interfaces. It’s not valid to specify multiple addresses when specifying the host for a connector; a connector makes a connection to one specific address.

port

This specified the port to connect to (when configuring a connector) or to listen on (when configuring an acceptor). The default value for this property is 61616.

tcpNoDelay

If this is true then Nagle’s algorithm will be disabled. This is a Java (client) socket option. The default value for this property is true.

tcpSendBufferSize

This parameter determines the size of the TCP send buffer in bytes. The default value for this property is 32768 bytes (32KiB).

TCP buffer sizes should be tuned according to the bandwidth and latency of your network. Here’s a good link that explains the theory behind this.

In summary TCP send/receive buffer sizes should be calculated as:

buffer_size = bandwidth * RTT.

Where bandwidth is in bytes per second and network round trip time (RTT) is in seconds. RTT can be easily measured using the ping utility.

For fast networks you may want to increase the buffer sizes from the defaults.

tcpReceiveBufferSize

This parameter determines the size of the TCP receive buffer in bytes. The default value for this property is 32768 bytes (32KiB).

writeBufferLowWaterMark

This parameter determines the low water mark of the Netty write buffer. Once the number of bytes queued in the write buffer exceeded the high water mark and then dropped down below this value, Netty’s channel will start to be writable again. The default value for this property is 32768 bytes (32KiB).

writeBufferHighWaterMark

This parameter determines the high water mark of the Netty write buffer. If the number of bytes queued in the write buffer exceeds this value, Netty’s channel will start to be not writable. The default value for this property is 131072 bytes (128KiB).

batchDelay

Before writing packets to the transport, Apache ActiveMQ Artemis can be configured to batch up writes for a maximum of batchDelay milliseconds. This can increase overall throughput for very small messages. It does so at the expense of an increase in average latency for message transfer. The default value for this property is 0 ms.

directDeliver

When a message arrives on the server and is delivered to waiting consumers, by default, the delivery is done on the same thread as that on which the message arrived. This gives good latency in environments with relatively small messages and a small number of consumers, but at the cost of overall throughput and scalability - especially on multi-core machines. If you want the lowest latency and a possible reduction in throughput then you can use the default value for directDeliver (i.e. true). If you are willing to take some small extra hit on latency but want the highest throughput set directDeliver to false.

nioRemotingThreads

This is deprecated. It is replaced by remotingThreads, if you are using this please update your configuration.

remotingThreads

Apache ActiveMQ Artemis will, by default, use a number of threads equal to three times the number of cores (or hyper-threads) as reported by Runtime.getRuntime().availableProcessors() for processing incoming packets. If you want to override this value, you can set the number of threads by specifying this parameter. The default value for this parameter is -1 which means use the value from Runtime.getRuntime().availableProcessors() * 3.

localAddress

When configured a Netty Connector it is possible to specify which local address the client will use when connecting to the remote address. This is typically used in the Application Server or when running Embedded to control which address is used for outbound connections. If the local-address is not set then the connector will use any local address available

localPort

When configured a Netty Connector it is possible to specify which local port the client will use when connecting to the remote address. This is typically used in the Application Server or when running Embedded to control which port is used for outbound connections. If the local-port default is used, which is 0, then the connector will let the system pick up an ephemeral port. valid ports are 0 to 65535

connectionsAllowed

This is only valid for acceptors. It limits the number of connections which the acceptor will allow. When this limit is reached a DEBUG level message is issued to the log, and the connection is refused. The type of client in use will determine what happens when the connection is refused. In the case of a core client, it will result in a org.apache.activemq.artemis.api.core.ActiveMQConnectionTimedOutException. Default value is -1 (unlimited)

handshake-timeout

Prevents an unauthorised client opening a large number of connections and just keeping them open. As connections each require a file handle this consumes resources that are then unavailable to other clients. Once the connection is authenticated, the usual rules can be enforced regarding resource consumption. Default value is set to 10 seconds. Each integer is valid value. When set value to zero or negative integer this feature is turned off. Changing value needs to restart server to take effect.

autoStart

Determines whether or not an acceptor will start automatically when the broker is started. Default value is true.

4.3. Configuring Netty Native Transport

Netty Native Transport support exists for selected OS platforms. This allows Apache ActiveMQ Artemis to use native sockets/io instead of Java NIO.

These Native transports add features specific to a particular platform, generate less garbage, and generally improve performance when compared to Java NIO based transport.

Both Clients and Server can benefit from this.

Current Supported Platforms.

• Linux running 64bit JVM

• MacOS running 64bit JVM

Apache ActiveMQ Artemis will by default enable the corresponding native transport if a supported platform is detected.

If running on an unsupported platform or any issues loading native libs, Apache ActiveMQ Artemis will fallback onto Java NIO.

4.3.1. Linux Native Transport

On supported Linux platforms Epoll is used, @see https://en.wikipedia.org/wiki/Epoll.

The following properties are specific to this native transport:

useEpoll

enables the use of epoll if a supported linux platform is running a 64bit JVM is detected. Setting this to false will force the use of Java NIO instead of epoll. Default is true

4.3.2. MacOS Native Transport

On supported MacOS platforms KQueue is used, @see https://en.wikipedia.org/wiki/Kqueue.

The following properties are specific to this native transport:

useKQueue

enables the use of kqueue if a supported MacOS platform running a 64bit JVM is detected. Setting this to false will force the use of Java NIO instead of kqueue. Default is true

4.4. Configuring Netty SSL

Netty SSL is similar to the Netty TCP transport but it provides additional security by encrypting TCP connections using the Secure Sockets Layer SSL

Please see the examples for a full working example of using Netty SSL.

Netty SSL uses all the same properties as Netty TCP but adds the following additional properties:

sslContext

An optional cache key only evaluated if org.apache.activemq.artemis.core.remoting.impl.ssl.CachingSSLContextFactory is active, to cache the initial created SSL context and reuse it. If not specified CachingSSLContextFactory will automatically calculate a cache key based on the given keystore/truststore parameters. See Configuring an SSLContextFactory for more details.

sslEnabled

Must be true to enable SSL. Default is false.

sslAutoReload

Must be true to have the broker ‘watch’ an acceptors keyStorePath and/or trustStorePath and invoke reload() on update. The watch period is controlled by the configuration reload feature. Default is false.

keyStorePath

When used on an acceptor this is the path to the SSL key store on the server which holds the server’s certificates (whether self-signed or signed by an authority).

When used on a connector this is the path to the client-side SSL key store which holds the client certificates. This is only relevant for a connector if you are using 2-way SSL (i.e. mutual authentication). Although this value is configured on the server, it is downloaded and used by the client. If the client needs to use a different path from that set on the server then it can override the server-side setting by either using the customary “javax.net.ssl.keyStore” system property or the ActiveMQ-specific “org.apache.activemq.ssl.keyStore” system property. The ActiveMQ-specific system property is useful if another component on the client is already making use of the standard Java system property.

keyStorePassword

When used on an acceptor this is the password for the server-side keystore.

When used on a connector this is the password for the client-side keystore. This is only relevant for a connector if you are using 2-way SSL (i.e. mutual authentication). Although this value can be configured on the server, it is downloaded and used by the client. If the client needs to use a different password from that set on the server then it can override the server-side setting by either using the customary “javax.net.ssl.keyStorePassword” system property or the ActiveMQ-specific “org.apache.activemq.ssl.keyStorePassword” system property. The ActiveMQ-specific system property is useful if another component on the client is already making use of the standard Java system property.

keyStoreType

The type of keystore being used. For example, JKS, JCEKS, PKCS12, PEM etc. This value can also be set via the “javax.net.ssl.keyStoreType” system property or the ActiveMQ-specific “org.apache.activemq.ssl.keyStoreType” system property. The ActiveMQ-specific system property is useful if another component on the client is already making use of the standard Java system property. Default is JKS.

keyStoreProvider

The provider used for the keystore. For example, SUN, SunJCE, etc. This value can also be set via the “javax.net.ssl.keyStoreProvider” system property or the ActiveMQ-specific “org.apache.activemq.ssl.keyStoreProvider” system property. The ActiveMQ-specific system property is useful if another component on the client is already making use of the standard Java system property. Default is null.

keyStoreAlias

When used on an acceptor this is the alias to select from the SSL key store (specified via keyStorePath) to present to the client when it connects.

When used on a connector this is the alias to select from the SSL key store (specified via keyStorePath) to present to the server when the client connects to it. This is only relevant for a connector when using 2-way SSL (i.e. mutual authentication).

Default is null.

trustStorePath

When used on an acceptor this is the path to the server-side SSL key store that holds the keys of all the clients that the server trusts. This is only relevant for an acceptor if you are using 2-way SSL (i.e. mutual authentication).

When used on a connector this is the path to the client-side SSL key store which holds the public keys of all the servers that the client trusts. Although this value can be configured on the server, it is downloaded and used by the client. If the client needs to use a different path from that set on the server then it can override the server-side setting by either using the customary “javax.net.ssl.trustStore” system property or the ActiveMQ-specific “org.apache.activemq.ssl.trustStore” system property. The ActiveMQ-specific system property is useful if another component on the client is already making use of the standard Java system property.

trustStorePassword

When used on an acceptor this is the password for the server-side trust store. This is only relevant for an acceptor if you are using 2-way SSL (i.e. mutual authentication).

When used on a connector this is the password for the client-side truststore. Although this value can be configured on the server, it is downloaded and used by the client. If the client needs to use a different password from that set on the server then it can override the server-side setting by either using the customary “javax.net.ssl.trustStorePassword” system property or the ActiveMQ-specific “org.apache.activemq.ssl.trustStorePassword” system property. The ActiveMQ-specific system property is useful if another component on the client is already making use of the standard Java system property.

trustStoreType

The type of truststore being used. For example, JKS, JCEKS, PKCS12, PEM etc. This value can also be set via the “javax.net.ssl.trustStoreType” system property or the ActiveMQ-specific “org.apache.activemq.ssl.trustStoreType” system property. The ActiveMQ-specific system property is useful if another component on the client is already making use of the standard Java system property. Default is JKS.

trustStoreProvider

The provider used for the truststore. For example, SUN, SunJCE, etc. This value can also be set via the “javax.net.ssl.trustStoreProvider” system property or the ActiveMQ-specific “org.apache.activemq.ssl.trustStoreProvider” system property. The ActiveMQ-specific system property is useful if another component on the client is already making use of the standard Java system property. Default is null.

enabledCipherSuites

Whether used on an acceptor or connector this is a comma separated list of cipher suites used for SSL communication. The default value is null which means the JVM’s default will be used.

enabledProtocols

Whether used on an acceptor or connector this is a comma separated list of protocols used for SSL communication. The default value is null which means the JVM’s default will be used.

needClientAuth

This property is only for an acceptor. It tells a client connecting to this acceptor that 2-way SSL is required. Valid values are true or false. Default is false.

wantClientAuth

This property is only for an acceptor. It tells a client connecting to this acceptor that 2-way SSL is requested but not required. Valid values are true or false. Default is false.

verifyHost

When used on a connector the CN or Subject Alternative Name values of the server’s SSL certificate will be compared with the hostname being connected to in order to verify a match. This is useful for both 1-way and 2-way SSL.

When used on an acceptor the CN or Subject Alternative Name values of the connecting client’s SSL certificate will be compared to its hostname to verify a match. This is useful only for 2-way SSL.

Valid values are true or false. Default is true for connectors, and false for acceptors.

trustAll

When used on a connector the client will trust the provided server certificate implicitly, regardless of any configured trust store.

Valid values are true or false. Default is false.

forceSSLParameters

When used on a connector any SSL settings that are set as parameters on the connector will be used instead of JVM system properties including both javax.net.ssl and ActiveMQ system properties to configure the SSL context for this connector.

Valid values are true or false. Default is false.

useDefaultSslContext

Only valid on a connector. Allows the connector to use the “default” SSL context (via SSLContext.getDefault()) which can be set programmatically by the client (via SSLContext.setDefault(SSLContext)). If set to true all other SSL related parameters except for sslEnabled are ignored.

Valid values are true or false. Default is false.

sslProvider

Used to change the SSL Provider between JDK and OPENSSL. The default is JDK. If used with OPENSSL you can add netty-tcnative to your classpath to use the native installed openssl. This can be useful if you want to use special ciphersuite - elliptic curve combinations which are support through openssl but not through the JDK provider. See https://en.wikipedia.org/wiki/Comparison_of_TLS_implementations for more information’s.

sniHost

When used on an acceptor the sniHost is a regular expression used to match the server_name extension on incoming SSL connections. If the name doesn’t match then the connection to the acceptor will be rejected. A WARN message will be logged if this happens. If the incoming connection doesn’t include the server_name extension then the connection will be accepted.

When used on a connector the sniHost value is used for the server_name extension on the SSL connection.

trustManagerFactoryPlugin

This is valid on either an acceptor or connector. It defines the name of the class which implements org.apache.activemq.artemis.api.core.TrustManagerFactoryPlugin. This is a simple interface with a single method which returns a javax.net.ssl.TrustManagerFactory. The TrustManagerFactory will be used when the underlying javax.net.ssl.SSLContext is initialized. This allows fine-grained customization of who/what the broker & client trusts.

This value takes precedence of all other SSL parameters which apply to the trust manager (i.e. trustAll, truststoreProvider, truststorePath, truststorePassword, crlPath).

Any plugin specified will need to be placed on the broker’s classpath.

4.4.1. Configuring an SSLContextFactory

If you use JDK as SSL provider (the default), you can configure which SSLContextFactory to use. Currently the following two implementations are provided:

• org.apache.activemq.artemis.core.remoting.impl.ssl.DefaultSSLContextFactory (registered by the default)

• org.apache.activemq.artemis.core.remoting.impl.ssl.CachingSSLContextFactory

You may also create your own implementation of org.apache.activemq.artemis.spi.core.remoting.ssl.SSLContextFactory.

The implementations are loaded by a java.util.ServiceLoader, thus you need to declare your implementation in a META-INF/services/org.apache.activemq.artemis.spi.core.remoting.ssl.SSLContextFactory file. If several implementations are available, the one with the highest priority will be selected.

So for example, if you want to use org.apache.activemq.artemis.core.remoting.impl.ssl.CachingSSLContextFactory you need to add a META-INF/services/org.apache.activemq.artemis.spi.core.remoting.ssl.SSLContextFactory file to your classpath with the content org.apache.activemq.artemis.core.remoting.impl.ssl.CachingSSLContextFactory.

A similar mechanism exists for the OPENSSL SSL provider in which case you can configure an OpenSSLContextFactory. Currently the following two implementations are provided:

• org.apache.activemq.artemis.core.remoting.impl.ssl.DefaultOpenSSLContextFactory (registered by the default)

• org.apache.activemq.artemis.core.remoting.impl.ssl.CachingOpenSSLContextFactory

You may also create your own implementation of org.apache.activemq.artemis.spi.core.remoting.ssl.OpenSSLContextFactory.

4.5. Configuring Netty HTTP

Netty HTTP tunnels packets over the HTTP protocol. It can be useful in scenarios where firewalls only allow HTTP traffic to pass.

Please see the examples for a full working example of using Netty HTTP.

Netty HTTP uses the same properties as Netty TCP but adds the following additional properties:

httpEnabled

Activates http on the client. This is not needed on the broker. With single port support Apache ActiveMQ Artemis will now automatically detect if http is being used and configure itself.

httpClientIdleTime

How long a client can be idle before sending an empty http request to keep the connection alive

httpClientIdleScanPeriod

How often, in milliseconds, to scan for idle clients

httpResponseTime

How long the server can wait before sending an empty http response to keep the connection alive

httpServerScanPeriod

How often, in milliseconds, to scan for clients needing responses

httpRequiresSessionId

If true the client will wait after the first call to receive a session id. Used the http connector is connecting to servlet acceptor (not recommended)

4.6. Configuring Netty SOCKS Proxy

All these parameters are only applicable to a connector and/or client URL.

socksEnabled

Whether or not to enable SOCKS support on the connector.

socksHost

The name of the SOCKS server to use.

socksPort

The port of the SOCKS server to use.

socksVersion

The version of SOCKS to use. Must be an integer. Default is 5.

socksUsername

The username to use when connecting to the socksHost.

socksPassword

The password to use when connecting to the socksHost. Only applicable if the socksVersion is 5.

socksRemoteDNS

Whether or not to create remote destination socket unresolved and disable DNS resolution. Default is false.