Connecting to hdfs/creating the sparksession from cdsw

[#1]

Hi Team,

I have installed the cdsw successfully but when I was trying to run the hdfs command/trying create the sparksession from the cdsw terminal then I am getting the below error. Any idea/suggestion what exactly i am missing here from set up of point of view? Thanks in Advance!!!

Error:

hdfs dfs -put data/sample_text_file.txt /tmp clouderamaster.<domain>.com
-put: java.net.UnknownHostException:

clouderamaster.<domain>.com: Is my cdh master server.

cdsw.<domain>.com: is the cdsw master.(from where I am running the hdfs /sparksession from the interactive command prompt/terminal)

[#2]

Also, just to add one more point i am unable to ping to clouderamaster from the cdsw master host in the cdsw terminal. Any suggestion guys what exactly i am missing here?

[#3]

@cjervis Sorry to tag you on the above query. Will you able to guide me where i am missing on the above issue?

[#4]

Unfortunately I do not have experience with CDSW but perhaps @tristanzajonc or @peter_ableda can be of assistance. 

[#5]

@cjervis Thanks for your quick response. 

[#6]

Hi,

You seem to have some network connectivity issue. I have seen many variations for this, please check

- that you don't have a firewall between the machines, 

- you resolve the hosts with DNS and not /etc/hosts

https://www.cloudera.com/documentation/data-science-workbench/1-3-x/topics/cdsw_known_issues.html#ne...

- DNS can do forward/reverse resolution on your master hostname/ip

I think if you are ok on the above, this should work.

Regards,

Peter

[#7]

@peter_ableda Thanks for your response.

Step 1: I have checked and could find we dont have any firewall between my machines.

Step 2:  DNS can do forward/reverse resolution on your master hostname/ip> Yes its working for cdswmaster host where I have installed cdsw(added to the dns entry as below which resolves forward as well as backword resolution)

Step 3: I have added 2 DNS entries as below for the cdswmaster host(cdswmaster.lab.test.com)

*.cdswmaster.lab.test.com  IN A IP

cdswmaster.lab.test.com     IN A IP

Little confused here do i need to add the dns names as above or do i need to change as cdsw(cdsw.lab.test.com) from cdswmaster as per the documentation.

Step 4: Checked the terminal from cdsw web ui and i am unable to ping to clouderamaster.lab.test.com(where cloudera manager was install). But I am able to ping to the terminal ip from the clouderamaster.lab.test.com.

I believe here some set up should be corrected inorder to ping the clouderamaster host correctly. Please advise

Also, do you see anyother set up i need to correct from my end to get going in cdsw. Sorry for little more demanding on the same as i find cdsw is little more complex interms of the set up.

[#8]

You need to make sure that forward/reverse DNS resolution works from the CDSW terminal to host where you have the YARN ResourceManager and HDFS NameNode services. You referred to this as clouderamaster.<domain>.com before.

This issue is not related to the CDSW master DNS resolution, you mentioned that you are using the session terminal, as it works, the CDSW master DNS is configured properly.

Regards,

Peter

[#9]

@peter_ableda Thanks Peter for your detailed explanation and your valuable time. Will check how I can access the CDH master node(YARN/HDFS Name Node) from my cdsw terminal.Not sure if the HTTP proxy set up will help or not.

[#10]

@peter_ableda  One Final Question. In my cdsw terminal the Ip addess was different(pod ip not the cdsw host ip) and that was the reason i am unable to connect to the master hostname(clouderamaster.<domain>.com) but i am able to ping using the master host ip from cdsw terminal. 

Also, I have not done hadoop Authentication in the cdsw admin web ui. Do you think its must to have access to the cluster and from where I can find the Principal/username and pwd/keytab to get access to the cluster. 

[#11]

Hi,

We have an overlay network on top of your CDSW hosts where the pods are getting their IPs from (100.66.x.x).

Based on your description it seems that DNS resolution is not working from inside the container while it works on the host. This can happen when multiple nameservers are configured in /etc/resolv.conf but some of them can't resolve your clouderamaster. You could figure out what nameserver can resolve your host and drop the rest of them or make sure that all nameservers can resolve the clouderamaster. 

I like to use `dig @nameserver clouderamaster.com` command to test these.

Regards,

Peter

[#12]

@peter_ableda Hi Peter, When we say we need to add the dns entry details of the master host. Are we trying to say we need to add the dns entry of the clouderamaster host dns entry or the cdswmaster dns entry?

As of now I have added the dns entry of the cdsw master host. Also, we need to add the xtra dot(.) after the hostname as per the documentation(*.cdsw.lab.test.com./cdsw.lab.test.com.)? Sorry I am little confused with the docs.

[#13]

The original issue you reported was an UnknownHostException on the clouderamaster.

hdfs dfs -put data/sample_text_file.txt /tmp clouderamaster.<domain>.com
-put: java.net.UnknownHostException:

You need to make sure that this host can be resolved (both forward/reverse) from inside a CDSW session via DNS.

As you can start a CDSW session and interact with it, you already configured the DNS entry for the CDSW master properly.

Regards,

Peter

[#14]

@peter_ableda You need to make sure that this host can be resolved (both forward/reverse) from inside a CDSW session via DNS. Is that means we need add another dns entry for the CDH master host(clouderamaster.lab.test.com) so that it can be accessiable from cdsw master host?

[#15 · Accepted solution]

Yes.

[#16]

@peter_ableda Thanks Peter. Now I am able to submit the spark job from cdsw master. Does cloudera provide the user level isoloation when they access to the cdsw project/content as different user can distrub /edit the same content?

[#17]

We have a collaboration page in the documentation:

https://www.cloudera.com/documentation/data-science-workbench/latest/topics/cdsw_collaborate.html

We also have a page about Kerberos authentication:

https://www.cloudera.com/documentation/data-science-workbench/latest/topics/cdsw_kerberos.html

I hope this answers your question.

Regards,

Peter

[#18]

@peter_ableda Thanks Peter for your time and have a grt day!