Tomcat7 SESSIONID keep changing after applied redis RedisSessionManager applies

I'm using tomcat7 with oracle-java8 in Ubuntu16.04.

And I start 2 different tomcat instances for load balancing, but the default behavior is that the session cannot share between them.

So I turned to the solution using RedisSessionManager in it.

After I add the below lines in the tomcat conf/context.xml file (of course I did added the dependency jars in the lib directory):

<Valve className="com.orangefunction.tomcat.redissessions.RedisSessionHandlerValve" /><Manager className="com.orangefunction.tomcat.redissessions.RedisSessionManager"             host="127.0.0.1"             port="6379"             database="0"             password="defuRedis2017"             maxInactiveInterval="60" />

Then start a single tomcat instance.

But after that, the server seemed cannot save session any more, and returned a different Set-Cookie header in each request, so the login cannot work any more even with a single tomcat instance.

If I comment out the above lines (in the context.xml file), the session works as expected.

So what makes it wrong to working with the RedisSesssionManager?