Got it Richard, thank you very much for the nice summary! I’m wondering what is the use case for delegation tokens on client side? Is it to support integration with Oozie?
I do know that Beeline is depending on Hadoop common and that is actually a very good example. I’ve seen sufficient number of users struggling with this dependency - using various workarounds for the classpath issue, having need to copy over Hadoop configuration files from real cluster (because otherwise portion of the security didn’t work at all, something with auth_to_local rules) and a lot of more. That is why I’m advising being careful here. Jarcec > On Dec 11, 2014, at 12:17 AM, Zhou, Richard <[email protected]> wrote: > > Hi Jarcec: > Thank you very much for your clarification about the history. > > The root cause for why we want to change "provided" to "compile" is to > implement "Delegation Token Support" [1], review board [2]. The status in > Hadoop is showed below. > Hadoop 2.5.1 or before: all classes used to implement Kerberos support is in > Hadoop-auth component, which depends only several libs with non-Hadoop > related lib. And it is added in Sqoop client side (shell component [3]) as > "compile" as we agreed before. > Hadoop 2.6.0: There is a refactor to support delegation token in Hadoop [4]. > Most components in Hadoop, such as RM, Httpfs and Kms, have rewritten > authentication mechanism to use delegation token. However, all delegation > token related class is in Hadoop-common instead of Hadoop-auth, because it > uses UserGroupInfomation class. > > So if Sqoop need to support delegation token, it has to include Hadoop-common > lib, because I believe that copying code is an unacceptable solution. Even > using Hadoop shims, which is a good solution to support different version of > Hadoop (I am +1 on writing a Hadoop shims in Sqoop like pig, hive etc.), the > Hadoop-common is also a dependency. For example, the client side (beeline) in > hive depends on Hadoop-common lib [5]. So I don't think it is a big problem > to add Hadoop-common in. > > Additionally, I agree with Abe that wire compatibility is another reason to > change "provided" to "compile", since it is in "Unstable" state. There will > be a potential problem in the future. > > So I prefer to add Hadoop-common lib as "compile" to make "Delegation Token > Support" happen. > > Add [email protected]. > > Links: > 1: https://issues.apache.org/jira/browse/SQOOP-1776 > 2: https://reviews.apache.org/r/28795/ > 3: https://github.com/apache/sqoop/blob/sqoop2/shell/pom.xml#L75 > 4: https://issues.apache.org/jira/browse/HADOOP-10771 > 5: https://github.com/apache/hive/blob/trunk/beeline/pom.xml#L133 > > Richard > > -----Original Message----- > From: Jarek Jarcec Cecho [mailto:[email protected]] On Behalf Of Jarek Jarcec > Cecho > Sent: Thursday, December 11, 2014 1:43 PM > To: [email protected] > Subject: Re: Hadoop as Compile time dependency in Sqoop2 > > Hi Abe, > thank you very much for surfacing the question. I think that there is a > several twists to it, so my apologies as this will be a long answer :) > > When we’ve started working on Sqoop 2 few years back, we’ve intentionally > pushed the Hadoop dependency as far from shared libraries as possible. The > intention was that no component in common or core should be depending nor use > any Hadoop APIs and those should be isolated to separate modules > (execution/submission engine). The reason for that is that Hadoop doesn’t > have particularly good track of keeping backward compatibility and it has > bitten a lot of projects in the past. For example every single project that I > know of that is using MR needs to have a shim layer that is dealing with the > API differences (Pig [1], Hive [2], …) . The only exception to this that I’m > aware of is Sqoop 1, where we did not had to introduce shims is only because > we (shamelessly) copied code from Hadoop to our own code base. Nevertheless > we have places where we had to do that detection nevertheless [3]. I’m sure > that Hadoop is getting better as the project matures, but I would still > advise being careful of using various Hadoop APIs and limit that usage to the > extend needed. There will be obviously situations where we want to use Hadoop > API to make our life simpler, such as reusing their security implementation > and that will be hopefully fine. > > Whereas we can be pretty sure that Sqoop Server will have Hadoop libraries on > the class-path and the concern there was more about introducing backward > incompatible changes that is hopefully less important nowadays, not > introducing Hadoop dependency on client side had a different reason. Hadoop > common is quite important jar that have huge number of dependencies - check > out the list at it’s pom file [4]. This is a problem because the Sqoop client > is meant to be small and easily reusable wheres depending on Hadoop will > force the application developer to certain library versions that are dictated > by Hadoop (like guava, commons-*). And that forces people to do various weird > things such as using custom class loaders to isolate those libraries from > main application and making the situation in most cases even worst, because > Hadoop libraries assumes “ownership” of the underlaying JVM and run a lot of > eternal threads per class-loader. Hence I would advise being double careful > when introducing dependency on Hadoop (common) for our client. > > I’m wondering what we’re trying to achieve by moving the dependency from > “provided” to “compile”? Do we want to just ensure that it’s always on the > Server side or is the intent to get it to the client? > > Jarcec > > Links: > 1: https://github.com/apache/pig/tree/trunk/shims/src > 2: https://github.com/apache/hive/tree/trunk/shims > 3: > https://github.com/apache/sqoop/blob/trunk/src/java/org/apache/sqoop/mapreduce/hcat/SqoopHCatUtilities.java#L962 > 4: > http://search.maven.org/#artifactdetails%7Corg.apache.hadoop%7Chadoop-common%7C2.6.0%7Cjar > >> On Dec 10, 2014, at 7:56 AM, Abraham Elmahrek <[email protected]> wrote: >> >> Hey guys, >> >> With the work being done in Sqoop2 involving authentication, there are >> a few classes that are being used from hadoop auth and eventually >> hadoop common. >> >> I'd like to gauge how folks feel about including the hadoop libraries >> as a "compile" time dependency rather than "provided". The reasons being: >> >> 1. Hadoop maintains wire compatibility within a major version: >> >> http://hadoop.apache.org/docs/stable/hadoop-project-dist/hadoop-common/Compatibility.html#Wire_compatibility >> 2. UserGroupInformation and other useful interfaces are marked as >> "Evolving" or "Unstable": >> >> http://hadoop.apache.org/docs/stable/hadoop-project-dist/hadoop-common/InterfaceClassification.html >> . >> >> I've been looking around and it seems most projects include Hadoop as >> a compile time dependency: >> >> 1. Kite - >> >> https://github.com/kite-sdk/kite/blob/master/kite-hadoop-dependencies/cdh5/pom.xml >> 2. Flume - https://github.com/apache/flume/blob/trunk/pom.xml >> 3. Oozie - https://github.com/apache/oozie/tree/master/hadooplibs >> 4. hive - https://github.com/apache/hive/blob/trunk/pom.xml#L1067 >> >> IMO wire compatibility is easier to maintain than Java API compatibility. >> There may be features in future Hadoop releases that we'll want to use >> on the security side as well. >> >> -Abe > > -- > You received this message because you are subscribed to the Google Groups > "intel-sqoop" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/a/cloudera.org/d/msgid/intel-sqoop/7F91673573F5D241AFCE8EDD6A313D24572C34%40SHSMSX103.ccr.corp.intel.com.
