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From "Leo Li" <liyilei1...@gmail.com>
Subject Re: [classlib][xnet] Problem using SSLSocketImpl behind load balancer
Date Wed, 11 Apr 2007 06:05:18 GMT
Hi, Gerald:
    First I would like to clarify your problem:
    1. We want to exchange the request to a new server seamlessly according
to workload balancing.
    2. The behavior of DNS caching prevent us from that.
    3. You would like to get the support from classlib, that is to enjoy the
DNS caching as well as the response to server switching.

    Since Harmony would like to be a compatible classlib with RI's, we have
to comply with RI's behavior with RI's.
    But it is possible to customize harmony's classlib if you conform with
apache license. So my suggestion is here:
    (1) Expose the method which clears the DNS cache in InetAddress to
public.(If you would like to maintain the interface of java public API, wrap
it in an implementation class and expose it as public.)
    (2) On the socket side, if you use your socket implementation, in the
connection method, if the connection fails, clear the DNS cache by the
method exposed before and retry it.
    If you are interested, I think, we might talk about it in detail.

On 4/11/07, Tim Ellison <t.p.ellison@gmail.com> wrote:
> Gerald Jerome wrote:
> > Hello, we are using the Apache Harmony SSLSocket classes to solve a
> problem
> > we were having with SSL renegotiation.  However, recently our production
> > admin noticed that our SSL client was not automatically failing over to
> a
> > secondary machine that exists behind a load balancer or redistributor in
> > cases where a server goes down (either unexpectedly or for
> maintenance).  We
> > are using the Sun JVM and not the Apache Harmony version.  He mentions
> the
> > following:
> That sounds like an interesting combination of code, and not something
> that I expect can be easily reproduced by the Harmony developers, so
> take the following information only as guidance -- I don't know what you
> are actually running with...
> > Our investigation found that once Java based clients (both standalone
> > applications, and servlets) have performed the first network access (i.e
> .
> > urlconnection, parsing of xml document with external references, etc)
> they
> > cache DNS settings, so any subsequent client request will use its old
> > information even if the real DNS settings have changed.
> >
> > To reset everything, you have to restart the client application since
> the
> > default JVM setting is to cache forever.
> >
> > The InetAddress class has a cache to store successful as well as
> > unsuccessful host name resolutions. The positive caching is there to
> guard
> > against DNS spoofing attacks.
> Correct, the scenario you describe is almost exactly as described here:
> http://www.rgagnon.com/javadetails/java-0445.html
> > He goes on to discuss how the caching can be disabled.  I know your
> > SSLSocket implementation uses SSLEngine and does low-level socket based
> > communication so I did not think his analysis may fit our situation.
> > Furthermore, I am not convinced that we are having this problem but our
> > development and test environments do not have a distributor/load
> balancer in
> > front of the actual host machines.
> Hmm, this could really be a shot in the dark then!
> > I know in production we are configured
> > to connect to the distributor, not one of the actual hosts.  I am
> wondering
> > if you were aware of any caching of DNS information that may be going on
> > inside the SSLSocket class and dependant code that we are using
> using?  I
> > could not find any references to the InetAddress class mentioned above
> in
> > any of the Harmony source I have.
> If you have the luni.jar then you should have the java.net.InetAddress
> class (and java.net.NegativeCache class).  They will honour the
> networkaddress.cache.ttl and networkaddress.cache.negative.ttl properties.
> > The x-net.jar file that we are using has
> > a last modified date of October 28, 2006 8:27:58 PM. The last modified
> date
> > of luni.jar is the same.  These are the only two Apache Harmony
> libraries we
> > are using.
> Those sound quite old now, although I don't recall significant
> development in x-net since then.
> > Any information you have pertaining to this problem is greatly
> > appreciated
> Maybe somebody else will have some insight, but it is really hard to
> advise on a problem you are not sure you are having on a runtime
> codebase we don't know.
> Regards,
> Tim

Leo Li
China Software Development Lab, IBM

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