Distributed Message Queue Module

Marius Ovidiu Bucur

Charles Chance

Sipcentric Ltd.

Olle E. Johansson

Edvina AB

Edited by

Marius Ovidiu Bucur

Charles Chance

Table of Contents

1. Admin Guide
1. Overview
2. Dependencies
2.1. Kamailio Modules
2.2. External Libraries or Applications
3. Parameters
3.1. server_address(str)
3.2. server_socket(str)
3.3. notification_address(str)
3.4. notification_channel(str)
3.5. multi_notify(int)
3.6. num_workers(int)
3.7. worker_usleep(int)
3.8. ping_interval(int)
4. Functions
4.1. dmq_handle_message([continue])
4.2. dmq_process_message([continue])
4.3. dmq_send_message(channel, node, body, content_type)
4.4. dmq_bcast_message(channel, body, content_type)
4.5. dmq_t_replicate([skip_loop_test])
4.6. dmq_is_from_node()
5. RPC Commands
5.1. dmq.list_nodes
5.2. dmq.remove
2. Developer Guide
1. dmq_load_api(dmq_api_t* api)
2. register_dmq_peer(dmq_peer_t* peer)
3. bcast_message(dmq_peer_t* peer, str* body, dmq_node_t* except, dmq_resp_cback_t* resp_cback, int max_forwards, str* content_type)
4. send_message(dmq_peer_t* peer, str* body, dmq_node_t* node, dmq_resp_cback_t* resp_cback, int max_forwards, str* content_type)

List of Examples

1.1. KDMQ Request Example
1.2. Set server_address parameter
1.3. Set server_socket parameter
1.4. Set notification_address parameter
1.5. Set notification_channel parameter
1.6. Set multi_notify parameter
1.7. Set num_workers parameter
1.8. Set worker_usleep parameter
1.9. Set ping_interval parameter
1.10. dmq_handle_message usage
1.11. dmq_process_message usage
1.12. dmq_send_message usage
1.13. dmq_bcast_message usage
1.14. dmq_t_replicate usage
1.15. dmq_is_from_node usage
1.16. dmq.list_nodes usage
1.17. dmq.remove usage
2.1. dmq_api_t structure
2.2. register_dmq_peer usage
2.3. bcast_message usage
2.4. send_message usage

Chapter 1. Admin Guide

1. Overview

The DMQ module implements a distributed message queue on top of Kamailio in order to facilitate data propagation and replication between multiple instances, referred as "nodes" (or "peers").

The DMQ data flow between nodes is grouped in a logical entity referred as "channel" (or "bus"), many flows (channels) can be active at the same time.

The communication between the nodes is done using SIP messages, after all Kamailio's best ability is routing SIP traffic, therefore reusing the same protocol empowers DMQ cluster with flexible routing policies, advanced authorization and security policies, a.s.o. DMQ sends SIP requests using the KDMQ request method (a custom method type specific to Kamailio, compliant with SIP specifications RFC3261). Data can be sent to all the other active nodes (aka "broadcast") or to a specific single node (aka "unicast").

The nodes can utilize the DMQ channels to pass messages between them to distribute data for various services (e.g., cached items, location records, active calls, ...). This grouping of messages on channels (per service) is similar to the topic concept in a typical pub/sub system. The channel name appears in the R-URI username part of KDMQ requests.

The DMQ cluster transparently deals with node discovery, availability, consistency, retransmissions, etc. A new node can join the DMQ cluster by sending an availability notification to an existing node in the clusters. Nodes that are not responding to KDMQ reguests are removed the from local list of active nodes, no longer being considered to be part of the KDMQ cluster.

Example 1.1. KDMQ Request Example

This request is generated for DMQ peers availability notifications. Other messages can be produced by various modules, with different R-URI username and body content, such as htable, dialog or usrloc modules.


KDMQ sip:notification_peer@ SIP/2.0
Via: SIP/2.0/UDP;branch=z9hG4bK55e5.423d95110000
To: <sip:notification_peer@>
From: <sip:notification_peer@>;tag=2cdb7a33a7f21abb98fd3a44968e3ffd-5b01
CSeq: 10 KDMQ
Call-ID: 1fe138e07b5d0a7a-50419@
Content-Length: 116
User-Agent: kamailio (4.3.0 (x86_64/linneaus))
Max-Forwards: 1
Content-Type: text/plain



2. Dependencies

2.1. Kamailio Modules

The following modules must be loaded before this module:

  • sl.

  • tm.

2.2. External Libraries or Applications

  • The DMQ module itself has no external dependencies. However, each peer may need to use its own (de)serialization mechanism, like JSON (via jannson module), XML (via xmlops) or string operations with transformations. .

3. Parameters

3.1. server_address(str)

The local server address. This is the addres with which the local DMQ node joins the servers group to send/receive messages.

Note: if server_socket is not set, then this address has to match a local socket, which will be used to send/receive messages.

Default value is NULL.

Example 1.2. Set server_address parameter

modparam("dmq", "server_address", "sip:")
modparam("dmq", "server_address", "sip:;transport=tls")

3.2. server_socket(str)

The local listen address. This is the interface over which the DMQ engine will send/receive messages.

Note: if this parameter is not set, the socket to send/receice messages is built from server_address parameter.

Default value is NULL.

Example 1.3. Set server_socket parameter

modparam("dmq", "server_socket", "udp:")

3.3. notification_address(str)

The address of another DMQ node from which the local node should retrieve initial information about all other nodes. This parameter can be specified multiple times in the configuration, to configure multiple notification servers. If you configure multiple notification servers, the multi_notify parameter needs to be disabled.

Default value is NULL.

Example 1.4. Set notification_address parameter

modparam("dmq", "notification_address", "sip:")
modparam("dmq", "notification_address", "sip:;transport=tls")

3.4. notification_channel(str)

The name of the channel for notifications about peers availability.

Default value is notification_peer.

Example 1.5. Set notification_channel parameter

modparam("dmq", "notification_channel", "peers")

3.5. multi_notify(int)

Enables the ability to resolve multiple IPv4/IPv6 addresses for a single notification address. Please note that this mode is not supported if you specify multiple notification address parameter.

A value of zero resolves to the first IP address found. A non-zero value resolves to all IP addresses associated with the host. This includes addresses from DNS SRV records, A and AAAA records.

Default value is 0.

Example 1.6. Set multi_notify parameter

modparam("dmq", "multi_notify", 1)

3.6. num_workers(int)

The number of worker threads for sending/receiving messages.

Default value is 2.

Example 1.7. Set num_workers parameter

modparam("dmq", "num_workers", 4)

3.7. worker_usleep(int)

The default locking/synchronisation mechanism between producer/consumer threads is the optimum for most environments. On some systems (e.g. FreeBSD) it can cause high CPU load and in such cases, it can be useful to disable locking and switch to polling for tasks at set intervals instead - putting the thread to sleep in-between and taking it out of process during that time.

A value >0 will disable the default locking and set the polling interval (in microseconds), which can be tuned to suit the specific environment.

Default value is 0 (recommended for most systems).

Example 1.8. Set worker_usleep parameter

modparam("dmq", "worker_usleep", 1000)

3.8. ping_interval(int)

The number of seconds between node pings (for checking status of other nodes).

Minimum value is 60 (default).

Example 1.9. Set ping_interval parameter

modparam("dmq", "ping_interval", 90)

4. Functions

4.1.  dmq_handle_message([continue])

Handles a DMQ message by passing it to the appropriate local peer (module). The peer is identified by the user part of the To header.

Meaning of parameters:

  • continue - by default, dmq_handle_message() will end execution of routing script. If this optional parameter is set to "1", dmq_handle_message() will continue executing the routing script after it's been called.

This function can be used from REQUEST_ROUTE.

Example 1.10. dmq_handle_message usage

    if(is_method("KDMQ")) {

4.2.  dmq_process_message([continue])

Similar to dmq_handle_message, but the processing is happening immediately, no longer cloning the request in shared memory to be passed to a DMQ worker process.

Meaning of parameters:

  • continue - by default, dmq_process_message() will end execution of routing script by returning 0. If this optional parameter is set to "1", dmq_process_message() will continue executing the routing script after it is been executed, returning 1.

This function can be used from REQUEST_ROUTE.

Example 1.11. dmq_process_message usage

    if(is_method("KDMQ")) {

4.3.  dmq_send_message(channel, node, body, content_type)

Sends a DMQ message directly from config file to a single node.

Meaning of parameters:

  • channel - name of the channel that should handle the message.

  • node - the SIP address of the node to which the message should be sent.

  • body - the message body.

  • content_type - the MIME type of the message body.

This function can be used from any route.

Example 1.12. dmq_send_message usage

	dmq_send_message("channel1", "sip:", "Message body...", "text/plain");

4.4.  dmq_bcast_message(channel, body, content_type)

Broadcasts a DMQ message from config file to all active nodes (except self) on the specific channel.

Meaning of parameters:

  • channel - name of the channel that should handle the message.

  • body - the message body.

  • content_type - the MIME type of the message body.

This function can be used from any route.

Example 1.13. dmq_bcast_message usage

    dmq_bcast_message("channel1", "Message body...", "text/plain");

4.5.  dmq_t_replicate([skip_loop_test])

Replicates the current SIP message to all active nodes (except self). Useful for replicating REGISTER, PUBLISH etc. in a clustered environment.

Meaning of parameters:

  • skip_loop_test - by default, DMQ checks the source IP of the message prior to replication, to ensure it has not been sent by another DMQ node (to avoid infinite loops). If this optional parameter is set to "1", the loop test is not performed. This makes sense, from a performance perspective, if you have already performed the necessary checks in the config script (see dmq_is_from_node()).

This function can be used from REQUEST_ROUTE only.

Example 1.14. dmq_t_replicate usage


4.6.  dmq_is_from_node()

Checks whether the current message has been sent by another active DMQ node in the cluster.

This function can be used from REQUEST_ROUTE only.

Example 1.15. dmq_is_from_node usage

	# basic example for REGISTER replication
    if(is_method("REGISTER")) {
        if (dmq_is_from_node()) {
            # coming from a DMQ node - already authenticated there
            # now just save contact, etc...
        } else {
            # coming from end point - authenticate, save contact, etc...
            dmq_t_replicate("1"); # source address checked, skip the loop test

5. RPC Commands

5.1. dmq.list_nodes

List the DMQ nodes. It has no parameters.

Example 1.16. dmq.list_nodes usage

kamcmd dmq.list_nodes

5.2. dmq.remove

Remove a DMQ node by address.


  • address - the SIP address of the DMQ node to remove.

Example 1.17. dmq.remove usage

kamctl rpc dmq.remove sip:

Chapter 2. Developer Guide

The module provides the following functions that can be used in other Kamailio modules.

1.  dmq_load_api(dmq_api_t* api)

This function binds the DMQ module and fills the structure with the exported functions below.

Example 2.1. dmq_api_t structure

typedef struct dmq_api {
	register_dmq_peer_t register_dmq_peer;
	bcast_message_t bcast_message;
	send_message_t send_message;
} dmq_api_t;

2.  register_dmq_peer(dmq_peer_t* peer)

Registers an entity as a DMQ peer which permits receiving/sending messages between nodes which support the same peer.

Example 2.2. register_dmq_peer usage

	Example to follow.

3.  bcast_message(dmq_peer_t* peer, str* body, dmq_node_t* except, dmq_resp_cback_t* resp_cback, int max_forwards, str* content_type)

Broadcast a DMQ message to all nodes in the DMQ bus excluding self, inactive nodes and "except" if specified.

Example 2.3. bcast_message usage

        Example to follow.

4.  send_message(dmq_peer_t* peer, str* body, dmq_node_t* node, dmq_resp_cback_t* resp_cback, int max_forwards, str* content_type)

Send a DMQ message to a single node.

Example 2.4. send_message usage

        Example to follow.