nchammas/flintrock

Mystery: Why doesn't SPARK_MASTER_IP accept actual IP addresses?

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#43 opened on Nov 5, 2015

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help wanted

Description

This is a mystery that someone can take on for fun or for glory.

If I change these two blocks of code from this:

master_host=master_instance.public_dns_name,
slave_hosts=[i.public_dns_name for i in slave_instances],

to this:

master_host=master_instance.ip_address,
slave_hosts=[i.ip_address for i in slave_instances],

then Spark fails to launch. master_host, in particular, gets plugged into SPARK_MASTER_IP in this template, which seems to set off the problem.

For whatever reason, DNS names work but IP addresses don't. I'm not sure why. Spark's documentation suggests that IP addresses should work.

I've probably misunderstood something about how to configure Spark. Another possibility is that there is a documentation or code bug in Spark itself that needs to be fixed.

One clue I've come across but not tested out is the fact that SPARK_MASTER_HOST is checked here, even though it is not mentioned anywhere else in the Spark codebase. I have a suspicion that SPARK_MASTER_HOST should instead be SPARK_MASTER_IP.

What I can say for certain is that this file is where some master configurations get set, and I have traced code there from start-master.sh. So it's probably a good place to start digging.

Contributor guide

Tech stack
python
Domain
clibackendcloud
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
needs investigation
Prerequisites
PythonApache SparkShell scripting
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Investigate the difference between SPARK MASTER IP and SPARK MASTER HOST in Spark's startup scripts. Look at the referenced files: flintrock.py lines 601-602 and 1165-1166, the template spark env.sh, and Spark's MasterArguments.scala. Determine why IP address causes failure while DNS name works. Possibly a bug in Spark's code where SPARK MASTER IP is not correctly handled. Also check if there is a workaround or if the issue is in Flintrock's usage.