The Mobicents SIP Load Balancer is used to balance the load of SIP service requests and responses between nodes in a Mobicents SIP Server cluster, such as Mobicents JAIN SLEE or SIP Servlets. Both Mobicents servers can be used in conjunction with the SIP load balancer to increase the performance and availability of SIP services and applications.
In terms of functionality, the Mobicents SIP load balancer is a simple stateless proxy server that intelligently forwards SIP session requests and responses between User Agents (UAs) on a Wide Area Network (WAN), and SIP Server nodes, which are almost always located on a Local Area Network (LAN). All SIP requests and responses pass through the SIP load balancer.
All User Agents send SIP messages, such as INVITE and MESSAGE, to the same SIP URI (the IP address and port number of the SIP load balancer on the WAN). The load balancer then parses, alters, and forwards those messages to an available node in the cluster. If the message was sent as a part of an existing SIP session, it will be forwarded to the cluster node which processed that User Agent's original transaction request.
The SIP Server that receives the message acts upon it and sends a response back to the SIP load balancer. The SIP load balancer reparses, alters and forwards the message back to the original User Agent. This entire proxying and provisioning process is carried out independent of the User Agent, which is only concerned with the SIP service or application it is using.
By using the load balancer, SIP traffic is balanced across a pool of available SIP Servers, increasing the overall throughput of the SIP service or application running on either individual nodes of the cluster. In the case of a Mobicents server with </distributed> capabilities, load balancing advantages are applied across the entire cluster.
The SIP load balancer is also able to fail over requests mid-call from unavailable nodes to available ones, thus increasing the reliability of the SIP service or application. The load balancer increases throughput and reliability by dynamically provisioning SIP service requests and responses across responsive nodes in a cluster. This enables SIP applications to meet the real-time demand for SIP services.
In addition to the SIP load balancing, there are several options for coordinated or cooperative load balancing with other protocols such as HTTP. Typically, a JBoss Application Server will use apache HTTP server with mod_jk, mod_proxy, mod_cluster or similar extension installed as an HTTP load balancer. This apache-based load balancer will parse incoming HTTP requests and it will look for the session ID of those requests in order to ensure all requests from the same session arrive at the same application server. By default, this is done by examining the jsessionid HTTP cookie or GET parameter and looking for the jvmRoute assigned to the session. The typical jsessionid value is of the form <sessionId>.<jvmRoute> (e.g. mysessionid323424.node1 where node1 is the jvmRoute component). The very first request for each new HTTP session do not have any session ID assigned, thus apache routes the request to a random application server node. When the node responds it assigns a session ID and jvmRoute to the response of the request in a HTTP cookie and this response goes back to the client through apache, which keeps track of which node owns which jvmRoute. Once, the very first request is served this way, the subsequent requests from this session will carry the assigned cookie and the apache load balancer will always route the requests to the node, which advertised itself as the jvmRoute owner.
Instead of using apache, an integrated HTTP load balancing is also available. The SIP load balancer has an HTTP port where you could direct all incoming HTTP requests. The integrated HTTP load balancer behaves exactly like apache by default, but this behaviour is extensible and can be overridden completely with the pluggable balancer algorithms. The integrated HTTP load balancer is much easier to configure and generally requires no effort, because it reuses most SIP settings ans assumes reasonable default values.
Unlike the native apache, the integrated HTTP load balancer is written completely in Java and does not support AJP, thus a performance penalty should be expected when using it. However, the integrated HTTP balancer has an advantage when related SIP and HTTP requests must stick to the same node.
The SIP/HTTP load balancer exposes an interface to allow users to customize the routing decision making for special purposes. By default there are three built-in algorithms. Only one algorithm is active at any time and it is specified with the algorithmClass property in the configuration file.
It is completely up to the algorithm how and whether to support distributed architecture or how to store the information needed for session affinity. The algorithms will be called for every SIP and HTTP request and other significant events to make more informed decisions.
Note
Users must be aware that, by default requests explicitly addressed to a live server node passing through the load balancer will be forwarded directly to the server node. This allows for pre-specified routing use-cases, where the target node is known by the SIP client through other means. If the target node is dead, then the node selection algorithm is used to route the request to an available node.
The following is a list of the built-in algorithms:
- org.mobicents.tools.sip.balancer.CallIDAffinityBalancerAlgorithm
This algorithm is not distributable. It selects nodes randomly to serve a give Call-ID extracted from the requests and responses. It keeps a map with
Call-ID -> nodeIdassociations and this map is not shared with other load balancers which will cause them to make different decisions. For HTTP it behaves like apache.- org.mobicents.tools.sip.balancer.HeaderConsistentHashBalancerAlgorithm
This algorithm is distributable and can be used in distributed load balancer configurations. It extracts the hash value of specific headers from SIP and HTTP messages to decide which application server node will handle the request. Information about the options in this algorithms is available in the balancer configuration file comments.
- org.mobicents.tools.sip.balancer.PersistentConsistentHashBalancerAlgorithm
This algorithm is distributable and is similar to the previous algorithm, but it attempts to keep session affinity even when the cluster nodes are removed or added, which would normally cause hash values to point to different nodes.
When the capacity of a single load balancer is exceeded, multiple load balancers can be used. With the help of an IP load balancer the traffic can be distributed between all SIP/HTTP load balancers based on some IP rules or round-robin. With consistent hash and jvmRoute-based balancer algorithms it doesn't matter which SIP/HTTP load balancer will process the request, because they would all make the same decisions based on information in the requests (headers, parameters or cookies) and the list of available nodes. With consistent hash algorithms there is no state to be preserved in the SIP/HTTP balancers.
Figure 1.2. Example deployment scenario with IP load balancers serving both directions for incoming and outgoing requests in a cluster
Each individual Mobicents SIP Server in the cluster is responsible for contacting the SIP load balancer and relaying its health status and regular "heartbeats".
From these health status reports and heartbeats, the SIP load balancer creates and maintains a list of all available and healthy nodes in the cluster. The load balancer forwards SIP requests between these cluster nodes, providing that the provisioning algorithm reports that each node is healthy and is still sending heartbeats.
If an abnormality is detected, the SIP load balancer removes the unhealthy or unresponsive node from the list of available nodes. In addition, mid-session and mid-call messages are failed over to a healthy node.
The SIP load balancer first receives SIP requests from endpoints on a port that is specified in its Configuration Properties configuration file. The SIP load balancer, using a round-robin algorithm, then selects a node to which it forwards the SIP requests. The load balancer forwards all same-session requests to the first node selected to initiate the session, providing that the node is healthy and available.
The Mobicents SIP load balancer appends itself to the Via header of each request, so that returned responses are sent to the SIP Balancer before they are sent to the originating endpoint.
The load balancer also adds itself to the path of subsequent requests by adding Record-Route headers. It can subsequently handle mid-call failover by forwarding requests to a different node in the cluster if the node that originally handled the request fails or becomes unavailable. The SIP load balancer immediately fails over if it receives and unhealthy status, or irregular heartbeats from a node.
In advanced configurations, it is possible to run more than one SIP load balancer. Simply edit the balancers connection string in your SIP Server - the list is separated with semi-colon.
Figure 1.3, “Basic IP and Port Cluster Configuration” describes a basic IP and Port Cluster Configuration. In the diagram, the SIP load balancer is the server with the IP address of 192.168.1.1.
Software Prerequisites
- A JAIN SIP HA-enabled application server such as Mobicents JAIN SLEE or Mobicents SIP Servlets is required.
Running the SIP load balancer requires at least two instances of the application server as cluster nodes nodes. Therefore, before configuring the SIP load balancer, we should make sure we've installed a the SIP application server first. The Mobicents SIP load balancer will work with a SIP Servlets-enabled JBoss Application Server or a JAIN SLEE application server with SIP RA.
SIP Servlets containers based on Tomcat are also supported but the session replication is not available there, thus mid-call failover will not work.
The load balancer is located in the sip-balancer top-level directory of the Mobicents distribution. You will find the following files in the directory:
The SIP load balancer executable JAR file can be placed anywhere in the file system. It is recommended that the file is placed in the directory containing other JAR executables, so it can be easily located in the future.
Procedure 1.1. Configuring the Mobicents SIP Load Balancer and SIP Server Nodes
Configure lb.properties Configuration Properties File
Configure the SIP load balancer's Configuration Properties file by substituting valid values for your personal setup. Example 1.1, “Complete Sample lb.properties File” shows a sample
lb.propertiesfile, with key element descriptions provided after the example. The lines beginning with the pound sign are comments.Example 1.1. Complete Sample lb.properties File
# Mobicents Load Balancer Settings # For an overview of the Mobicents Load Balancer visit http://docs.google.com/present/view?id=dc5jp5vx_89cxdvtxcm # The Load balancer will listen for both TCP and UDP connections # The binding address of the load balancer. This also specifies the # default value for both internalHost and externalHost if not specified separately. host=127.0.0.1 # The binding address of the load balancer where clients should connect (if the host property is not specified) #externalHost=127.0.0.1 # The SIP port from where servers will receive messages # delete if you want to use only one port for both inbound and outbound) internalPort=5065 # The SIP port used where clients should connect externalPort=5060 # The binding address of the load balancer where SIP application servers should connect (if the host property is not specified) #internalHost=127.0.0.1 # The RMI port used for heartbeat signals rmiRegistryPort=2000 # The HTTP port for HTTP forwarding # if you like to activate the integrated HTTP load balancer, this is the entry point httpPort=2080 #If no nodes are active the LB can redirect the traffic to the unavailableHost specified in this property, #otherwise, it will return 503 Service Unavailable #unavailableHost=google.com # If you are using IP load balancer, put the IP address and port here #externalIpLoadBalancerAddress=127.0.0.1 #externalIpLoadBalancerPort=111 # Requests initited from the App Servers can route to this address (if you are using 2 IP load balancers for bidirectional SIP LB) #internalIpLoadBalancerAddress=127.0.0.1 #internalIpLoadBalancerPort=111 # The addresses in the SIP LB Via headers can be either the real addresses or those specified in the external and internal IP LB addresses useIpLoadBalancerAddressInViaHeaders=false # Designate extra IP addresses as serer nodes #extraServerNodes=222.221.21.12:21,45.6.6.7:9003,33.5.6.7,33.9.9.2 # Call-ID affinity algortihm settings. This algorithm is the default. No need to uncomment it. #algorithmClass=org.mobicents.tools.sip.balancer.CallIDAffinityBalancerAlgorithm # This property specifies how much time to keep an association before being evitcted. # It is needed to avoid memory leaks on dead calls. The time is in seconds. #callIdAffinityMaxTimeInCache=500 # Uncomment to enable the consistent hash based on Call-ID algorithm. #algorithmClass=org.mobicents.tools.sip.balancer.HeaderConsistentHashBalancerAlgorithm # This property is not required, it defaults to Call-ID if not set, cna be "from.user" or "to.user" when you want the SIP URI username #sipHeaderAffinityKey=Call-ID #specify the GET HTTP parameter to be used as hash key #httpAffinityKey=appsession # Uncomment to enable the persistent consistent hash based on Call-ID algorithm. #algorithmClass=org.mobicents.tools.sip.balancer.PersistentConsistentHashBalancerAlgorithm # This property is not required, it defaults to Call-ID if not set #sipHeaderAffinityKey=Call-ID #specify the GET HTTP parameter to be used as hash key #httpAffinityKey=appsession #This is the JBoss Cache 3.1 configuration file (with jgroups), if not specified it will use default #persistentConsistentHashCacheConfiguration=/home/config.xml # Call-ID affinity algortihm settings. This algorithm is the default. No need to uncomment it. #algorithmClass=org.mobicents.tools.sip.balancer.CallIDAffinityBalancerAlgorithm # This property specifies how much time to keep an association before being evitcted. # It is needed to avoid memory leaks on dead calls. The time is in seconds. #callIdAffinityMaxTimeInCache=500 # Uncomment to enable the consistent hash based on Call-ID algorithm. #algorithmClass=org.mobicents.tools.sip.balancer.HeaderConsistentHashBalancerAlgorithm # This property is not required, it defaults to Call-ID if not set, cna be "from.user" or "to.user" when you want the SIP URI username #sipHeaderAffinityKey=Call-ID #specify the GET HTTP parameter to be used as hash key #httpAffinityKey=appsession # Uncomment to enable the persistent consistent hash based on Call-ID algorithm. #algorithmClass=org.mobicents.tools.sip.balancer.PersistentConsistentHashBalancerAlgorithm # This property is not required, it defaults to Call-ID if not set #sipHeaderAffinityKey=Call-ID #specify the GET HTTP parameter to be used as hash key #httpAffinityKey=appsession #This is the JBoss Cache 3.1 configuration file (with jgroups), if not specified it will use default #persistentConsistentHashCacheConfiguration=/home/config.xml #If a node doesnt check in within that time (in ms), it is considered dead nodeTimeout=5100 #The consistency of the above condition is checked every heartbeatInterval milliseconds heartbeatInterval=5000 #JSIP stack configuration..... javax.sip.STACK_NAME = SipBalancerForwarder javax.sip.AUTOMATIC_DIALOG_SUPPORT = off # You need 16 for logging traces. 32 for debug + traces. # Your code will limp at 32 but it is best for debugging. gov.nist.javax.sip.TRACE_LEVEL = 0 // Specify if message contents should be logged. gov.nist.javax.sip.LOG_MESSAGE_CONTENT=false gov.nist.javax.sip.DEBUG_LOG = logs/sipbalancerforwarderdebug.txt gov.nist.javax.sip.SERVER_LOG = logs/sipbalancerforwarder.xml gov.nist.javax.sip.THREAD_POOL_SIZE = 64 gov.nist.javax.sip.REENTRANT_LISTENER = true- host
Local IP address, or interface, on which the SIP load balancer will listen for incoming requests.
- externalPort
Port on which the SIP load balancer listens for incoming requests from SIP User Agents.
- internalPort
Port on which the SIP load balancer forwards incoming requests to available, and healthy, SIP Server cluster nodes.
- rmiRegistryPort
Port on which the SIP load balancer will establish the RMI heartbeat connection to the application servers. When this connection fails or a disconnection instruction is received, an application server node is removed and handling of requests continues without it by redirecting the load to the lie nodes.
- httpPort
Port on which the SIP load balancer will accept HTTP requests to be distributed across the nodes.
- internalTransport
Transport protocol for the internal SIP connections associated with the internal SIP port of the load balancer. Possible choices are
UDP,TCPandTLS.- externalTransport
Transport protocol for the external SIP connections associated with the external SIP port of the load balancer. Possible choices are
UDP,TCPandTLS. It must match the transport of the internal port.- externalIpLoadBalancerAddress
Address of the IP load balancer (if any) used for incoming requests to be distributed in the direction of the application server nodes. This address may be used by the SIP load balancer to be put in SIP headers where the external address of the SIP load balancer is needed.
- externalIpLoadBalancerPort
The port of the external IP load balancer. Any messages arriving at this port should be distributed across the external SIP ports of a set of SIP load balancers.
- internalIpLoadBalancerAddresst
Address of the IP load balancer (if any) used for outgoing requests (requests initiated from the servers) to be distributed in the direction of the clients. This address may be used by the SIP load balancer to be put in SIP headers where the internal address of the SIP load balancer is needed.
- internalIpLoadBalancerPort
The port of the internal IP load balancer. Any messages arriving at this port should be distributed across the internal SIP ports of a set of SIP load balancers.
- extraServerNodes
Comma-separated list of hosts that are server nodes. You can put here alternative names of the application servers here and they will be recognized. Names are important, because they might be used for direction-analysis. Requests coming from these server will go in the direction of the clients and will not be routed back to the cluster.
- algorithmClass
The fully-qualified Java class name of the balancing algorithm to be used. There are three algorithms to choose from and you can write your own to implement more complex routing behaviour. Refer to the sample configuration file for details about the available options for each algorithm. Each algorithm can have algorithm-specific properties for fine-grained configuration.
- nodeTimeout
In milliseonds. Default value is 5100. If a server node doesnt check in within this time (in ms), it is considered dead.
- heartbeatInterval
In milliseconds. Default value is 5000 milliseonds. The hearbeat interval must be the same or close to the interval specified in the JAIN SIP property on the server machines -
org.mobicents.ha.javax.sip.HEARTBEAT_INTERVAL
Note
The remaining keys and properties in the configuration properties file can be used to tune the JAIN SIP stack, but are not specifically required for load balancing. To assist with tuning, a comprehensive list of implementing classes for the SIP Stack is available from the Interface SIP Stack page on nist.gov. For a comprehensive list of properties associated with the SIP Stack implementation, refer to Class SipStackImpl page on nist.gov.
Configure logging
The SIP load balancer uses Java Logging as a logging mechanism. As such you cna configure it through a property file and specify the property file to be used by using the following command
-Djava.util.logging.config.file=./lb-logging.properties. Please refer to JDK logging for more informationon how to configure the Java logging.
The Mobicents SIP load balancer can work in concert with HTTP load balancers such as mod_jk. Whenever an HTTP session is bound to a particular node, an instruction is sent to the SIP load balancer to direct the SIP calls from the same application session to the same node.
It is sufficient to configure mod_jk to work for HTTP in JBoss in order to enable cooperative load balancing. Mobicents will read the configuration and will use it without any extra configuration. You can read more about configuring mod_jk with JBoss in your JBoss Application Server documentation.
To use the integrated HTTP load balancer, no extra configuration is needed. If a unique jvmRoute is specified and enabled in each application server, it will behave exactly as the apache balancer. If jvmRoute is not present it will use session ID as a hash value and attempt to create sticky session. The integrated balancer can be used together with the apache balancer at the same time.
In addition to the apache behaviour, there is a consistent hash balancer algorithm that can be enabled for both HTTP and SIP messages. For both HTTP and SIP messages, there is a configurable affinity key, which is evaluated and hashed against each unassigned request. All requests with the same hash value will always be routed to the same application server node. For example, the SIP affinity key could be the callee user name and the HTTP affinity key could the “appsession” HTTP GET parameter of the request. If the desired behaviour group these requests, we can just make sure the affinity values (user name and GET parameter) are the same.
Procedure 1.2. Running the SIP Load Balancer and SIP Server Nodes
Start the SIP Load Balancer
Start the SIP load balancer, ensuring the Configuration Properties file (
lb.propertiesin this example) is specified. In the Linux terminal, or using the Windows Command Prompt, the SIP Load Balancer is started by issuing a command similar to this one:java -jar sip-balancer-jar-with-dependencies.jar lb-configuration.properties
Executing the SIP load balancer produces output similar to the following example:
home]$ java -jar sip-balancer-jar-with-dependencies.jar lb-configuration.properties Oct 21, 2008 1:10:58 AM org.mobicents.tools.sip.balancer.SIPBalancerForwarder start INFO: Sip Balancer started on address 127.0.0.1, external port : 5060, port : 5065 Oct 21, 2008 1:10:59 AM org.mobicents.tools.sip.balancer.NodeRegisterImpl startServer INFO: Node registry starting... Oct 21, 2008 1:10:59 AM org.mobicents.tools.sip.balancer.NodeRegisterImpl startServer INFO: Node expiration task created Oct 21, 2008 1:10:59 AM org.mobicents.tools.sip.balancer.NodeRegisterImpl startServer INFO: Node registry started
The output shows the IP address on which the SIP load balancer is listening, as well as the external and internal listener ports.
Configure SIP Server Nodes
The information about configuring your SIP Server, SIP Servlets or JAIN SLEE, is in the respective server User Guide.
Start Load Balancer Client Nodes
Start all SIP load balancer client nodes.
To test load balancing, the same application must be deployed manually on each node. Two SIP Softphones must be installed.
Procedure 1.3. Testing Load Balancing with Sip Servlets
Deploy an Application
Ensure that for each node, the DAR file location is specified in the
server.xmlfile.Deploy the Location service manually on both nodes.
Start the "Sender" SIP softphone
Start a SIP softphone client with the SIP address of
sip:sender@sip-servlets-com, listening on port 5055. The outbound proxy must be specified as the sip-balancer (http://127.0.0.1:5060)Start the "Receiver" SIP softphone
Start a SIP softphone client with the SIP address of
sip:receiver-failover@sip-servlets-com, listening on port 5090.Initiate two calls from "Sender" SIP softphone
Initiate one call from
sip:sender@sip-servlets-comtosip:receiver-failover@sip-servlets-com. Tear down the call once completed.Initiate a second call using the same SIP address, and tear down the call once completed. Notice that the call is handled by the second node.
Assuming that you started the JBoss Application Server as a foreground process in the Linux terminal, the easiest way to stop it is by pressing the Ctrl+C key combination in the same terminal in which you started it.
This should produce similar output to the following:
^COct 21, 2008 1:11:57 AM org.mobicents.tools.sip.balancer.SipBalancerShutdownHook run INFO: Stopping the sip forwarder