Chapter 5. Supported components
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# Chapter 5. Supported components

## Tigase Advanced Clustering Strategy for Multi User Chat (ACS-MUC)

Tigase Team <team@tigase.com> v3.3.0-SNAPSHOT, 2022-11-30 :numbered:

### Overview

ACS for MUC allows seamless clustering of MUC rooms across Tigase XMPP server cluster installation. ACS for MUC is required for clustered MUC deployments. If offers various strategies to handle distribution of traffic and rooms across the cluster, which allows fine-tune configuration of the deployment to individual needs.

### Tigase ACS MUC Configuration

In order to use ACS for MUC, main Advance Clustering Strategy is required. Once it’s enabled, clustered version of MUC component will be selected by default during startup therefore it’s not required to configure it explicitly (make sure no class is configured).

    muc () {}

It’s also possible to explicitly configure the class with the following configuration:

    muc (class: tigase.muc.cluster.MUCComponentClustered) {}

With the above configuration default MUC clustering strategy will be used. In order to select different strategy you have to configure it’s class in `strategy` bean within `muc` component bean:

    muc () {
        strategy (class: tigase.muc.cluster.ShardingStrategy) {}
    }

### ACS MUC Strategies

#### ShardingStrategy

This is default clustering strategy used by Tigase ACS - MUC component. It should be used in most cases when we do not have small number of rooms with many occupants.

##### Short description

This is default clustering strategy used by Tigase ACS - MUC component. In this strategy MUC rooms are partitioned so each room is hosted only on one node. Every node contains full list of rooms with list of occupants available in each room and map which contains room address as a key and node as a value. If room is already opened (hosted) on some node, then node hosting this room is resolved using map of room to node. In other case node is selected by hash of room address using following algorithm

    Math.abs(roomJid.hashCode()) % connectedNodes.size()

which gives a index of node on connected nodes list. So if node is not opened, then every cluster node should forward packets related to this room to the same node.

##### Connection to cluster

Once node connects to a cluster then map of hosted rooms and it’s occupants is synchronized between connecting node and any other already connected node.

##### Disconnection from cluster

If node is disconnected from a cluster due to server failure, then every other node will send "kick" stanzas to every occupant of every room hosted on disconnected node.

If node is disconnected due to node shutdown then node which is shutting down will send "kick" stanzas on it’s own, but it will notify every node about shutdown before disconnection from cluster.

##### Configuration

This is default strategy thus it’s used if no strategy configuration is present, but if you wish to enable this strategy and keep it enabled even if deafult clustering strategy will change in the future then you need to set `class` property of `strategy` bean within `muc` component to `tigase.muc.cluster.ShardingStrategy`.

Example:

    muc () {
        strategy (class: tigase.muc.cluster.ShardingStrategy) {}
    }

#### ClusteredRoomStrategy

This is clustering strategy which can be used for by Tigase ACS - MUC component, which is recommended for installations with relatively few rooms but rooms itself having a lot of occupants.

##### Short description

In this strategy MUC rooms are persistent and each room is hosted on every node. Every node contains full list of rooms (as they are persistent). Room on each node has knowledge only about occupants which joined room on this node. If remote user has joined room on one node and then it’s packets are delivered by S2S to other node, then packets will be forwarded to node to on which user joined room. Packets from user are processed by node on which they joined to room and notifications about joining room, leaving room, change of presences or about new message are sent to all other nodes and those other nodes are responsible for delivering proper notifications to users which joined room on them.

##### Connection to cluster

Once node connects to a cluster then map of occupants and their rooms are synchronized with other nodes.

##### Disconnection from cluster

If node is disconnected from a cluster, then every other node will send "kick" stanzas to every occupant of every room hosted on disconnected node.

##### Configuration

To enable this strategy you have to set `class` property of `strategy` bean within `muc` component to `tigase.muc.cluster.ClusteredRoomStrategy`.

Example:

    muc () {
        strategy (class: tigase.muc.cluster.ClusteredRoomStrategy) {}
    }

#### ClusteredRoomStrategyV2

This is clustering strategy which can be used for by Tigase ACS - MUC component, which is recommended for installations with relatively few rooms but rooms itself having a lot of occupants - contains improvements over ClusteredRoomStrategy

##### Short description

In this strategy MUC rooms are persistent and each room is hosted on every node. Every node contains full list of rooms (as they are persistent). Room on each node has knowledge only about occupants which joined room on this node. If remote user has joined room on one node and then it’s packets are delivered by S2S to other node, then packets will be forwarded to node to on which user joined room. Packets from user are processed by node on which they joined to room and notifications about joining room, leaving room, change of presences or about new message are sent to all other nodes and those other nodes are responsible for delivering proper notifications to users which joined room on them.

This version contains improvements over the section called “ClusteredRoomStrategy” which leads to improved performance and reduced trafic over cluster connection due to changes in logic of processing packets.

##### Connection to cluster

Once node connects to a cluster then map of occupants and their rooms are synchronized with other nodes.

##### Disconnection from cluster

If node is disconnected from a cluster, then every other node will send "kick" stanzas to every occupant of every room hosted on disconnected node.

##### Configuration

To enable this strategy you have to set `class` property of `strategy` bean within `muc` component to `tigase.muc.cluster.ClusteredRoomStrategyV2`.

Example:

    muc () {
        strategy (class: tigase.muc.cluster.ClusteredRoomStrategyV2) {}
    }

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