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From "Haohui Mai (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8828) Support distcp from secure to insecure clusters
Date Fri, 04 Oct 2013 17:51:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8828?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13786411#comment-13786411

Haohui Mai commented on HADOOP-8828:

I'm reopening this JIRA as we found some subtle problems in HADOOP-10016 and HADOOP-10017.

I've tested the set up of copying from a secure Hadoop cluster to secure Hadoop 2 cluster
using distcp, and have found some subtle problems:

1. There is a NPE in the trunk which fails the distcp job (addressed in HADOOP-10017).
2. When copying from a secure Hadoop 1 cluster to an insecure Hadoop 2 cluster, the Hadoop
1 cluster cannot handle this case because it lacks of negotiation and fallback mechanisms
during authentications. (addressed in HADOOP-10016).

> Support distcp from secure to insecure clusters
> -----------------------------------------------
>                 Key: HADOOP-8828
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8828
>             Project: Hadoop Common
>          Issue Type: Bug
>            Reporter: Eli Collins
> Users currently can't distcp from secure to insecure clusters.
> Relevant background from ATM:
> There's no plumbing to make the HFTP client use AuthenticatedURL in the case security
is enabled. This means that even though you have the servlet filter correctly configured on
the server, the client doesn't know how to properly authenticate to that filter.
> The crux of the issue is that security is enabled globally instead of per-file system.
The trick of using HFTP as the source FS works when the source is insecure, but not the source
is secure.
> Normal cp with two hdfs:// URL can be made to work. There is indeed logic in o.a.h.ipc.Client
to fall back to using simple authentication if your client config has security enabled (hadoop.security.authentication
set to "kerberos") and the server responds with a response for simple authentication. Thing
is, there are at least 3 bugs with this that I bumped into. All three can be worked around.
> 1) If your client config has security enabled you *must* have a valid Kerberos TGT, even
if you're interacting with an insecure cluster. The hadoop client unfortunately tries to read
the local ticket cache before it tries to connect to the server, and so doesn't know that
it won't need Kerberos credentials.
> 2) Even though the destination NN is insecure, it has to have a Kerberos principal created
for it. You don't need a keytab, and you don't need to change any settings on the destination
NN. The principal just needs to exist in the principal database. This is again because the
hadoop client will, before connecting to the remote NN, try to get a service ticket for the
hdfs/f.q.d.n principal for the remote NN. If this fails, it won't even get to the part where
it tries to connect to the insecure NN and falls back to simple auth.
> 3) Once you get through problems 1 and 2, you will try to connect to the remote, insecure
NN. This will work, but the reported principal name of your user will include a realm that
the remote NN doesn't know about. You will either need to change the default_realm setting
in /etc/krb5.conf on the insecure NN to be the same as the secure NN, or you will need to
add some custom hadoop.security.auth_to_local mappings on the insecure NN so it knows how
to translate this long principal name into a short name.
> Even with all these changes, distcp still won't work since the first thing it tries to
do when submitting the job is to get a delegation token for all the involved NNs, which won't
work since the insecure NN isn't running a DT secret manager. I haven't been able to figure
out a way around this, except to make a custom distcp which doesn't necessarily do this.

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