https://community.cloudera.com/t5/Support-Questions/Null-Pointer-Exception-in-ambari-server-logs-after-ambari/m-p/230539#M192389 <P>Now that I think more about this, I guess that </P><PRE>Unable to connect to: <A href="https://hadoop-m:8441/agent/v1/register/hadoop-m.c.hdp-1-163209.internal">https://hadoop-m:8441/agent/v1/register/hadoop-m.c.hdp-1-163209.internal</A> </PRE><P>started to occur when ambari server started to throw NPEs, which I detected right after (re)starting it, which I did right after I copied HUE to ambari's stack with:</P><PRE>sudo git clone <A href="https://github.com/EsharEditor/ambari-hue-service.git">https://github.com/EsharEditor/ambari-hue-service.git</A> /var/lib/ambari-server/resources/stacks/HDP/$VERSION/services/HUE</PRE><P>(which are the very first steps of HUE installation guide via ambari).</P><P>Regarding FQDNs, connectivity ambari server &lt;-&gt; ambari agents and handshake/registration ports (8440/8441).</P><P>@hadoop-m</P><PRE>$ more /etc/hosts 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain610.132.0.4 hadoop-m.c.hdp-1-163209.internal hadoop-m # Added by Google 169.254.169.254 metadata.google.internal # Added by Google </PRE><PRE>$ hostname -f hadoop-m.c.hdp-1-163209.internal </PRE><P>@hadoop-w-0</P><PRE>127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 10.132.0.2 hadoop-w-0.c.hdp-1-163209.internal hadoop-w-0 # Added by Google 169.254.169.254 metadata.google.internal # Added by Google</PRE><PRE>$ hostname -f hadoop-w-0.c.hdp-1-163209.internal</PRE><PRE>$ telnet hadoop-m 8440 Trying 10.132.0.4... Connected to hadoop-m. Escape character is '^]'.</PRE><PRE>$ telnet hadoop-m 8441 Trying 10.132.0.4... Connected to hadoop-m. Escape character is '^]'. </PRE><PRE>$ openssl s_client -connect hadoop-m:8440 CONNECTED(00000003) (... I removed lines ...) --- Server certificate -----BEGIN CERTIFICATE----- MIIFnDCCA4SgAwIBAgIBATAN (...I removed rest...) </PRE><PRE>$ openssl s_client -connect hadoop-m:8441 CONNECTED(00000003) (... I removed lines ...) -----BEGIN CERTIFICATE----- MIIFnDCCA4SgAwIBAgIBAT (...I removed rest...) </PRE><P>@hadoop-w-1</P><PRE>$ more /etc/hosts 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 10.132.0.3 hadoop-w-1.c.hdp-1-163209.internal hadoop-w-1 # Added by Google 169.254.169.254 metadata.google.internal # Added by Google</PRE><PRE>$ hostname -f hadoop-w-1.c.hdp-1-163209.internal </PRE><PRE>$ telnet hadoop-m 8440 Trying 10.132.0.4... Connected to hadoop-m. Escape character is '^]'.</PRE><PRE>$ telnet hadoop-m 8441 Trying 10.132.0.4... Connected to hadoop-m. Escape character is '^]'.</PRE><PRE>$ openssl s_client -connect hadoop-m:8440 CONNECTED(00000003) (... I removed lines ...) --- Server certificate -----BEGIN CERTIFICATE----- MIIFnDCCA4SgAwIBAgIBATAN (...I removed rest...)</PRE><PRE>$ openssl s_client -connect hadoop-m:8441 CONNECTED(00000003) (... I removed lines ...) -----BEGIN CERTIFICATE----- MIIFnDCCA4SgAwIBAgIBAT (...I removed rest...)</PRE><P>It looks as it should, doesn't it?</P> Wed, 17 May 2017 02:07:08 GMT rafael_gomez_g 2017-05-17T02:07:08Z