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https://issues.apache.org/jira/browse/HDFS-14118?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16755491#comment-16755491
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Íñigo Goiri commented on HDFS-14118:
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{quote}
I have some confusions about the RESOLVE_SERVICE_KEY. Do you mean to put it
into core-default.xml file? Since this config is for per cluster service
discovery service, if we move it to the common, we will have to put all of the
different resolvers into the core-site.xml as well.
{quote}
Right, this is kind of sticky.
I guess the point is that we would have different implementations not only per
namespace but also in YARN, HDFS, Commons, etc.
In any case, we should move {{createDomainNameResolver()}} to the commons and
use {{ReflectionUtils#newInstance()}} instead of what we have there.
In that method we can pass the conf and the conf key to instantiate from.
{quote}
For the MockDomainNameResolver, since what it basically does is to return some
predefined fake values, will it make more sense for individual tests to have it
so that they can apply their own values?
{quote}
I'd like to make this whole resolver self contained, for that reason is better
if we have a full unit test just for it in commons.
Then others can extend it if so.
{quote}
When you say `Move the setup for DNS to a function`, do you mean all of the
line 252-257 to a separate function? This doesn't bring much benefit to the
code in my opinion. Can you elaborate?
{quote}
I was referring to lines 137-158.
I would make this a function (e.g., {{addDNSSettings()}}) and then in
{{testResolveDomainNameUsingDNS()}}, do:
{code}
Configuration dnsConf = new Configuration(conf);
addDNSSettings(dnsConf);
{code}
> Use DNS to resolve Namenodes and Routers
> ----------------------------------------
>
> Key: HDFS-14118
> URL: https://issues.apache.org/jira/browse/HDFS-14118
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Fengnan Li
> Assignee: Fengnan Li
> Priority: Major
> Attachments: DNS testing log, HDFS-14118.001.patch,
> HDFS-14118.002.patch, HDFS-14118.003.patch, HDFS-14118.004.patch,
> HDFS-14118.005.patch, HDFS-14118.006.patch, HDFS-14118.007.patch,
> HDFS-14118.008.patch, HDFS-14118.patch
>
>
> Clients will need to know about routers to talk to the HDFS cluster
> (obviously), and having routers updating (adding/removing) will have to make
> every client change, which is a painful process.
> DNS can be used here to resolve the single domain name clients knows to a
> list of routers in the current config. However, DNS won't be able to consider
> only resolving to the working router based on certain health thresholds.
> There are some ways about how this can be solved. One way is to have a
> separate script to regularly check the status of the router and update the
> DNS records if a router fails the health thresholds. In this way, security
> might be carefully considered for this way. Another way is to have the client
> do the normal connecting/failover after they get the list of routers, which
> requires the change of current failover proxy provider.
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