Upgrade guide for instances running High Availability (active/passive) previous to 2.249.2.3

<!-- HA setup; may be overridden with $JENKINS_HOME/jgroups.xml -->
<config xmlns="urn:org:jgroups"
        xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="urn:org:jgroups https://www.jgroups.org/schema/jgroups-4.0.xsd">
    <TCP_NIO2
         recv_buf_size="${tcp.recv_buf_size:128K}"
         send_buf_size="${tcp.send_buf_size:128K}"
         max_bundle_size="64K"
         sock_conn_timeout="1000"

         bind_port="${HA_BIND_PORT}"
         port_range="${HA_PORT_RANGE}"
         diagnostics_port="${HA_DIAGNOSTIC_PORT}"

         thread_pool.enabled="true"
         thread_pool.min_threads="1"
         thread_pool.max_threads="10"
         thread_pool.keep_alive_time="5000"/>

    <CENTRAL_LOCK />

    <com.cloudbees.jenkins.ha.singleton.CHMOD_FILE_PING
             location="${HA_JGROUPS_DIR}"
             remove_old_coords_on_view_change="true"/>
    <MERGE3 max_interval="30000"
            min_interval="10000"/>
    <FD_SOCK/>
    <FD timeout="3000" max_tries="3" />
    <VERIFY_SUSPECT timeout="1500"  />
    <BARRIER />
    <pbcast.NAKACK2 use_mcast_xmit="false"
                    discard_delivered_msgs="true"/>
    <UNICAST3 />
    <!--
      When a new node joins a cluster, initial message broadcast doesn't necessarily seem
      to arrive. Using a shorter cycles in the STABLE protocol makes the cluster recognize
      this dropped transmission and cause a retransmission.
    -->
    <pbcast.STABLE stability_delay="1000" desired_avg_gossip="50000"
                   max_bytes="4M"/>
    <pbcast.GMS print_local_addr="true" join_timeout="3000"
                view_bundling="true"
                max_join_attempts="5"/>
    <MFC max_credits="2M"
         min_threshold="0.4"/>
    <FRAG2 frag_size="60K"  />
    <pbcast.STATE_TRANSFER />
    <!-- pbcast.FLUSH  /-->
</config>

<!-- HA setup; may be overridden with $JENKINS_HOME/jgroups.xml -->
<config xmlns="urn:org:jgroups"
        xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="urn:org:jgroups https://www.jgroups.org/schema/JGroups-3.1.xsd">
    <TCP_NIO2
         recv_buf_size="${tcp.recv_buf_size:128K}"
         send_buf_size="${tcp.send_buf_size:128K}"
         max_bundle_size="64K"
         max_bundle_timeout="30"
         sock_conn_timeout="1000"

         bind_port="${HA_BIND_PORT}"
         port_range="${HA_PORT_RANGE}"
         diagnostics_port="${HA_DIAGNOSTIC_PORT}"

         timer_type="new"
         timer.min_threads="4"
         timer.max_threads="10"
         timer.keep_alive_time="3000"
         timer.queue_max_size="500"

         thread_pool.enabled="true"
         thread_pool.min_threads="1"
         thread_pool.max_threads="10"
         thread_pool.keep_alive_time="5000"
         thread_pool.queue_enabled="false"
         thread_pool.queue_max_size="100"
         thread_pool.rejection_policy="discard"

         oob_thread_pool.enabled="true"
         oob_thread_pool.min_threads="1"
         oob_thread_pool.max_threads="8"
         oob_thread_pool.keep_alive_time="5000"
         oob_thread_pool.queue_enabled="false"
         oob_thread_pool.queue_max_size="100"
         oob_thread_pool.rejection_policy="discard"/>

    <CENTRAL_LOCK />

    <com.cloudbees.jenkins.ha.singleton.CHMOD_FILE_PING
             location="${HA_JGROUPS_DIR}"
             remove_old_coords_on_view_change="true"
             remove_all_files_on_view_change="true"/>
    <MERGE2 max_interval="30000"
            min_interval="10000"/>
    <FD_SOCK/>
    <FD timeout="3000" max_tries="3" />
    <VERIFY_SUSPECT timeout="1500"  />
    <BARRIER />
    <pbcast.NAKACK2 use_mcast_xmit="false"
                   discard_delivered_msgs="true"/>
    <UNICAST />
    <!--
      When a new node joins a cluster, initial message broadcast doesn't necessarily seem
      to arrive. Using a shorter cycles in the STABLE protocol makes the cluster recognize
      this dropped transmission and cause a retransmission.
    -->
    <pbcast.STABLE stability_delay="1000" desired_avg_gossip="50000"
                   max_bytes="4M"/>
    <pbcast.GMS print_local_addr="true" join_timeout="3000"
                view_bundling="true"
                max_join_attempts="5"/>
    <MFC max_credits="2M"
         min_threshold="0.4"/>
    <FRAG2 frag_size="60K"  />
    <pbcast.STATE_TRANSFER />
    <!-- pbcast.FLUSH  /-->
</config>