I understand that that is how the port is *later* retrieved, but how does the namenode know the port in the first place? i.e. if the datanode sends a packet to the namenode, how does the namenode know what port # the datanode server is running on?
On Sun, Dec 22, 2013 at 10:28 PM, Shekhar Sharma <shekhar2...@gmail.com>wrote: > Check the version file > During the startup Datanode sends out a heart beat signal and NN > assigns a storageID for it which is unique for every datanode. > Using the storage id it identify the ip and port of a datanode > Regards, > Som Shekhar Sharma > +91-8197243810 > > > On Mon, Dec 23, 2013 at 9:41 AM, Dhaivat Pandya <dhaivatpan...@gmail.com> > wrote: > > Hi, > > > > I'm currently trying to build a cache layer that should sit "on top" of > the > > datanode. Essentially, the namenode should know the port number of the > > cache layer instead of that of the datanode (since the namenode then > relays > > this information to the default HDFS client). All of the communication > > between the datanode and the namenode currently flows through my cache > > layer (including heartbeats, etc.) > > > > *First question*: is there a way to tell the namenode where a datanode > > should be? Any way to trick it into thinking that the datanode is on a > port > > number where it actually isn't? As far as I can tell, the port number is > > obtained from the DatanodeId object; can this be set in the configuration > > so that the port number derived is that of the cache layer? > > > > I spent quite a bit of time on the above question and I could not find > any > > sort of configuration option that would let me do that. So, I delved into > > the HDFS source code and tracked down the DatanodeRegistration class. > > However, I can't seem to find out *how* the NameNode figures out the > > Datanode's port number or if I could somehow change the packets to > reflect > > the port number of cache layer? *Second question: *how does the namenode > > figure out a newly-registered Datanode's port number? > > > > Thank you, > > > > Dhaivat >
