Problems in YARN: Why only SecondaryNameNode started? [Solved]

I was configuring a YARN cluster and after all set I tried to start services.
./start-dfs.sh
./start-yarn.sh

To my surprise, I only see SecondaryNameNode service got started. What? I didn't configure the SecondaryNameNode service, also where is my NameNode service which I really want?

I also checked the log and it says that:

The log shows that port 50070 already in use. But I run a command:

lsof -i:50070

There is nothing there using the port.

Also the host address is 0.0.0.0, this seems very wrong.
I checked many posts and they all didn't guide me to the root cause. Finally I found out the root cause

[Solution]

in hdfs-site.xml, there is one entry that's necessary:

dfs.http.address
myHostNodename:50070

If you want your secondary namenode, please add another one

dfs.secondary.http.address
my2ndHostNodename:50090

Happy World!

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Feelings and Experiences of CCD-333 Exam - Cloudera Certified Developer for Apache Hadoop (CCDH)

In October this year, I took a Cloudera Certified Developer for Apache Hadoop exam, which number is CCD-333. I successfully passed the exam, and looking back upon, all the efforts paid had value. This is a new exam and there is few materials in the internet talking about it, now I want to write something to share my feelings and experiences, which may help people who are preparing for the exam.


Part 1: Exam Preparation - Learning
1. Hadoop The Definite Guide 3rd


This is the book you must read before the exam, which explain very well and in details of Hadoop. I took a three days training by Cloudera certified trainer, but that class is an overview level training and is not very detailed. After the exam, I found the many questions examed are in the Definite Guide book rather than the training.
And very important, it's better that you read very carefully of Chapter 2 to 8 of this book, and maybe add chapter 9 and 10. I read them twice. But for chapter 11 to 16 which talks about the ecosystem of Hadoop (HBase, Hive, Pig etc.) , you don't need to read them if only for preparing the exam.

Part 2: The Exam CCD-333
The CCD-333 exam is 90 minutes with 60 questions, and the requirement is to score 67% or above. The exam tests many areas, the section scores below listing them precisely:

I feel that it exams a lot in the Input and Outpout of MapReduce, you need to understand the flow and details of MapReduce, and in the exam itself, I feel that time is sufficient to finish the exam.

Part 3: The certification

I wish this article is helpful for those who are preparing for this exam. All the best!

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