# Apache Tomcat 6.0

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# Apache Tomcat Configuration Reference

## The Cluster Membership object

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Introduction

> The membership component in the Apache Tribes Channel is responsible for dynamic discovery of other members(nodes) in the cluster.

Default Implementation

> The default implementation of the cluster group notification is built on top of multicast heartbeats sent using UDP packets to a multicast IP address. Cluster members are grouped together by using the same multicast address/port combination. Each member sends out a heartbeat with a given interval (`frequency`), and this heartbeat is used for dynamic discovery. In a similar fashion, if a heartbeat has not been received in a timeframe specified by `dropTime` ms. a member is considered suspect and the channel and any membership listener will be notified.

Attributes

> Multicast Attributes

> > Attribute | Description
> > --- | ---
> > `className` | The default value is `org.apache.catalina.tribes.membership.McastService` and is currently the only implementation. This implementation uses multicast heartbeats for member discovery.

> > `address`

> > The multicast address that the membership will broadcast its presence and listen for other heartbeats on. The default value is `228.0.0.4` Make sure your network is enabled for multicast traffic.
> > The multicast address, in conjunction with the `port` is what creates a cluster group. To divide up your farm into several different group, or to split up QA from production, change the `port` or the `address`
> > Previously known as mcastAddr.

> > `port` | The multicast port, the default value is `45564` The multicast port, in conjunction with the `address` is what creates a cluster group. To divide up your farm into several different group, or to split up QA from production, change the `port` or the `address`
> > `frequency` | The frequency in milliseconds in which heartbeats are sent out. The default value is `500` ms. In most cases the default value is sufficient. Changing this value, simply changes the interval in between heartbeats.

> > `dropTime`

> > The membership component will time out members and notify the Channel if a member fails to send a heartbeat within a give time. The default value is `3000` ms. This means, that if a heartbeat is not received from a member in that timeframe, the membership component will notify the cluster of this.
> > On a high latency network you may wish to increase this value, to protect against false positives.
> > Apache Tribes also provides a `TcpFailureDetector` that will verify a timeout using a TCP connection when a heartbeat timeout has occurred. This protects against false positives.

> > `bind` | Use this attribute if you wish to bind your multicast traffic to a specific network interface. By default, or when this attribute is unset, it tries to bind to `0.0.0.0` and sometimes on multihomed hosts this becomes a problem.
> > `ttl` | The time-to-live setting for the multicast heartbeats. This setting should be a value between 0 and 255. The default value is VM implementation specific.
> > `domain` | Apache Tribes has the ability to logically group members into domains, by using this domain attribute. The `org.apache.catalina.tribes.Member.getDomain()` method returns the value specified here.
> > `soTimeout` | The sending and receiving of heartbeats is done on a single thread, hence to avoid blocking this thread forever, you can control the `SO_TIMEOUT` value on this socket. If a value smaller or equal to 0 is presented, the code will default this value to frequency

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