tomcat cluster: member changes of an existing attribute object not replicated

Question

Tomcat cluster in kubernetes: member changes of session existing object are not replicated.

Server.xml:

<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"/>
  </Channel>
</Cluster>

e.g.,

Foo foo = (Foo)session.getAttribute("foo");
foo.setName("new Foo");

The changed foo is not replicated to other nodes. DeltaManager is used by default:

  org.apache.catalina.ha.session.DeltaManager

Does DeltaManager work for session.setAttribute(...) only?

Is there a way to replicate the whole session (or real diff) after each request?