DNSMembershipProvider (Apache Tomcat 9.0.111 API Documentation)
Description: declaration: package: org.apache.catalina.tribes.membership.cloud, class: DNSMembershipProvider

# Class DNSMembershipProvider

java.lang.Object
org.apache.catalina.tribes.membership.MembershipProviderBase
org.apache.catalina.tribes.membership.cloud.CloudMembershipProvider
org.apache.catalina.tribes.membership.cloud.DNSMembershipProvider

All Implemented Interfaces:
  `ChannelListener, Heartbeat, MembershipProvider`

public class DNSMembershipProvider extends CloudMembershipProvider
A `MembershipProvider` that uses DNS to retrieve the members of a cluster.

Configuration example for Kubernetes

`server.xml`

    <Server ...

      <Service ...

        <Engine ...

          <Host ...

            <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster">
              <Channel className="org.apache.catalina.tribes.group.GroupChannel">
                <Membership className="org.apache.catalina.tribes.membership.cloud.CloudMembershipService"
                    membershipProviderClassName="org.apache.catalina.tribes.membership.cloud.DNSMembershipProvider"/>
              </Channel>
            </Cluster>
            ...

minimal example for the Service my-tomcat-app-membership, note the selector
`dns-membership-service.yml`

    apiVersion: v1
    kind: Service
    metadata:
      annotations:
        service.alpha.kubernetes.io/tolerate-unready-endpoints: "true"
        description: "The service for tomcat cluster membership."
      name: my-tomcat-app-membership
    spec:
      clusterIP: None
      selector:
        app: my-tomcat-app

First Tomcat pod minimal example, note the labels that must correspond to the selector in the service.
`tomcat1.yml`

    apiVersion: v1
    kind: Pod
    metadata:
      name: tomcat1
      labels:
        app: my-tomcat-app
    spec:
      containers:
      - name: tomcat
        image: tomcat
        ports:
        - containerPort: 8080

Environment variable configuration
`DNS_MEMBERSHIP_SERVICE_NAME=my-tomcat-app-membership`

- ## Field Summary

  ### Fields inherited from class CloudMembershipProvider

  `connectionTimeout, CUSTOM_ENV_PREFIX, expirationTime, headers, localIp, md5, port, readTimeout, sm, startTime, streamProvider, url`

  ### Fields inherited from class MembershipProviderBase

  `executor, membership, membershipListener, service`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `DNSMembershipProvider()`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `boolean`
  `accept(Serializable msg, Member sender)`
  Invoked by the channel to determine if the listener will process this message or not.
  `protected Member[]`
  `fetchMembers()`
  Fetch current cluster members from the cloud orchestration.
  `void`
  `start(int level)`
  Start the membership provider.
  `boolean`
  `stop(int level)`
  Stop the membership provider.

  ### Methods inherited from class CloudMembershipProvider

  `getEnv, getNamespace, heartbeat, init, messageReceived, updateMember`

  ### Methods inherited from class MembershipProviderBase

  `getMember, getMembers, hasMembers, setMembershipListener, setMembershipService`

  ### Methods inherited from class Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Constructor Details

  - ### DNSMembershipProvider

    public DNSMembershipProvider()

- ## Method Details

  - ### start

    public void start(int level) throws Exception
    Description copied from interface: `MembershipProvider`
    Start the membership provider.
    Specified by:
      `start` in interface `MembershipProvider`
    Overrides:
      `start` in class `CloudMembershipProvider`
    Parameters:
      `level` - the readiness level
      - Channel.DEFAULT - will start all services
      - Channel.MBR_RX_SEQ - starts the membership receiver
      - Channel.MBR_TX_SEQ - starts the membership broadcaster
    Throws:
      `Exception` - if an error occurs

  - ### stop

    public boolean stop(int level) throws Exception
    Description copied from interface: `MembershipProvider`
    Stop the membership provider.
    Specified by:
      `stop` in interface `MembershipProvider`
    Overrides:
      `stop` in class `CloudMembershipProvider`
    Parameters:
      `level` - the readiness level
      - Channel.DEFAULT - will stop all services
      - Channel.MBR_RX_SEQ - stops the membership receiver
      - Channel.MBR_TX_SEQ - stops the membership broadcaster
    Returns:
      `true` if successful
    Throws:
      `Exception` - if an error occurs

  - ### fetchMembers

    protected Member[] fetchMembers()
    Description copied from class: `CloudMembershipProvider`
    Fetch current cluster members from the cloud orchestration.
    Specified by:
      `fetchMembers` in class `CloudMembershipProvider`
    Returns:
      the member array

  - ### accept

    public boolean accept(Serializable msg, Member sender)
    Description copied from interface: `ChannelListener`
    Invoked by the channel to determine if the listener will process this message or not.
    Specified by:
      `accept` in interface `ChannelListener`
    Overrides:
      `accept` in class `CloudMembershipProvider`
    Parameters:
      `msg` - Serializable
      `sender` - Member
    Returns:
      boolean