# &adminguide;

## 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.

IMPORTANT: DMQ must be used only between Kamailio instances having same major version. Internal structures can be incompatible between different major versions and can lead to crashes or unexpected behaviour.

Possible DMQ node statuses:

- DMQ_NODE_ACTIVE "active" = node is in dmq node list and responded with response code 200 OK, to KDMQ message. At startup, all nodes are considered active, regardless of their actual state.

- DMQ_NODE_NOT_ACTIVE "not_active" = node is in dmq node list and did not respond to KDMQ message (408 timeout).

- DMQ_NODE_DISABLED "disabled" = node will be deleted from dmq node list.

### KDMQ Request

KDMQ messages can have different format and content for R-URI username, headers and body, being specific to each component that leverages DMQ to replicate data, such as htable, dialog or usrloc modules.

Next request is generated by DMQ module for peers availability notifications.

#### KDMQ Request Example

    ...

    KDMQ sip:notification_peer@192.168.40.15:5090 SIP/2.0
    Via: SIP/2.0/UDP 192.168.40.15;branch=z9hG4bK55e5.423d95110000
    To: <sip:notification_peer@192.168.40.15:5090>
    From: <sip:notification_peer@192.168.40.15:5060>;tag=2cdb7a33a7f21abb98fd3a44968e3ffd-5b01
    CSeq: 10 KDMQ
    Call-ID: 1fe138e07b5d0a7a-50419@192.168.40.15
    Content-Length: 116
    User-Agent: kamailio (4.3.0 (x86_64/linneaus))
    Max-Forwards: 1
    Content-Type: text/plain

    sip:192.168.40.16:5060;status=active
    sip:192.168.40.15:5060;status=disabled
    sip:192.168.40.17:5060;status=not_active

    ...

## Dependencies

### &kamailio; Modules

The following modules must be loaded before this module:

- sl.

- tm.

### 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. .

## Parameters

### `server_address`(str)

The local server address. This is the address 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.

#### Set `server_address` parameter

    ...
    modparam("dmq", "server_address", "sip:10.0.0.20:5060")
    ...
    modparam("dmq", "server_address", "sip:10.0.0.20:5061;transport=tls")
    ...

### `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/receive messages is built from server_address parameter.

Default value is NULL.

#### Set `server_socket` parameter

    ...
    modparam("dmq", "server_socket", "udp:10.0.0.20:5060")
    ...

### `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.

#### Set `notification_address` parameter

    ...
    modparam("dmq", "notification_address", "sip:10.0.0.21:5060")
    ...
    modparam("dmq", "notification_address", "sip:10.0.0.21:5061;transport=tls")
    ...

### `notification_channel`(str)

The name of the channel for notifications about peers availability.

Default value is notification_peer.

#### Set `notification_channel` parameter

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

### `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.

#### Set `multi_notify` parameter

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

### `num_workers`(int)

The number of worker threads for sending/receiving messages.

Default value is 2.

#### Set `num_workers` parameter

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

### `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).

#### Set `worker_usleep` parameter

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

### `ping_interval`(int)

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

Minimum value is 60 (default).

#### Set `ping_interval` parameter

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

### `remove_inactive`(int)

A value of zero disable removing dmq nodes. Node status will be changed to not_active. A non-zero value (default is 1) enable removing nodes. For node that is defined as notification address status will be changed to not_active. Otherwise it will be marked as disabled and then will be removed.

Default value is 1.

#### Set `remove_inactive` parameter

    ...
    modparam("dmq", "remove_inactive", 0)
    ...

### `fail_count_enabled`(int)

Enable per node counting of failed responses.

Default value is 0 (disabled).

#### Set `fail_count_enabled` parameter

    ...
    modparam("dmq", "fail_count_enabled", 1)
    ...

### `fail_count_threshold_not_active`(int)

DMQ node status change from "active" to "not_active" if 408 fail counts are greater than this threshold value: This threshold can be reached both via internal DMQ notification ping mechanism, and other modules that use dmq to broadcast messages:

- Fail counts reset every time a node responds with response code 200 OK, on response callback of notification ping.

- Fail counts increase every time a node responds with response code 408, on response callback of notification ping.

- Fail counts increase every time a node responds with response code 408, on response callback of other modules that use dmq, only if node is in "active" state.

Default value is 0. Move node to "not_active" state on first fail.

#### Set `fail_count_threshold_not_active` parameter

    ...
    modparam("dmq", "fail_count_threshold_not_active", 100)
    ...

### `fail_count_threshold_disabled`(int)

DMQ node status change from "not_active" to "disabled" if 408 fail counts are greater than this threshold value. This threshold can be reached only via internal DMQ notification ping mechanism:

- Fail counts reset every time a node responds with response code 200 OK, on response callback of notification ping.

- Fail counts increase every time a node responds with response code 408, on response callback of notification ping.

Default value is 1. Move node to "disabled" state on second fail.

#### Set `fail_count_threshold_disabled` parameter

    ...
    modparam("dmq", "fail_count_threshold_disabled", 105)
    ...

## Functions

### `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.

#### `dmq_handle_message` usage

    ...
        if(is_method("KDMQ")) {
            dmq_handle_message();
        }
    ...

### `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.

#### `dmq_process_message` usage

    ...
        if(is_method("KDMQ")) {
            dmq_process_message();
        }
    ...

### `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.

#### `dmq_send_message` usage

    ...
    	dmq_send_message("channel1", "sip:10.0.0.21:5060", "Message body...", "text/plain");
    ...

### `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.

#### `dmq_bcast_message` usage

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

### `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.

#### `dmq_t_replicate` usage

    ...
        dmq_t_replicate();
    ...

### `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.

#### `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
            }
        }
    ...

## RPC Commands

### dmq.list_nodes

List the DMQ nodes. It has no parameters.

#### dmq.list_nodes usage

    ...
    &kamctl; rpc dmq.list_nodes
    ...

### dmq.remove

Remove a DMQ node by address.

Parameters:

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

#### dmq.remove usage

    ...
    &kamctl; rpc dmq.remove sip:1.2.3.4:5060
    ...