Hadoop HBase localhost considerations

When installing Hadoop HBase on (Ubuntu?) Linux you might run into some strange problems concerning networking when you try to start your new installed HBase node in a development mode where you only run one node on your local system. The issue might manifest itself first in your log files when you try to find out why things are not running as expected. On of the things you might see is something like this; Failed setting up proxy interface org.apache.hadoop.hbase.ipc.HRegionInterface to localhost/127.0.0.1:34908 after attempts=1

This message is somewhere in your logfile joining a complete java error stack, an example of the error stack can be found below and in fact is only a WARN level message however can mess things up quite a bid;

2012-11-20 09:29:08,473 WARN org.apache.hadoop.hbase.master.AssignmentManager: Failed assignment of -ROOT-,,0.70236052 to localhost,34908,1353400143063, trying to assign elsewhere instead; retry=0
org.apache.hadoop.hbase.client.RetriesExhaustedException: Failed setting up proxy interface org.apache.hadoop.hbase.ipc.HRegionInterface to localhost/127.0.0.1:34908 after attempts=1
 at org.apache.hadoop.hbase.ipc.HBaseRPC.handleConnectionException(HBaseRPC.java:291)
 at org.apache.hadoop.hbase.ipc.HBaseRPC.waitForProxy(HBaseRPC.java:259)
 at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.getHRegionConnection(HConnectionManager.java:1313)
 at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.getHRegionConnection(HConnectionManager.java:1269)
 at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.getHRegionConnection(HConnectionManager.java:1256)
 at org.apache.hadoop.hbase.master.ServerManager.getServerConnection(ServerManager.java:550)
 at org.apache.hadoop.hbase.master.ServerManager.sendRegionOpen(ServerManager.java:483)
 at org.apache.hadoop.hbase.master.AssignmentManager.assign(AssignmentManager.java:1640)
 at org.apache.hadoop.hbase.master.AssignmentManager.assign(AssignmentManager.java:1363)
 at org.apache.hadoop.hbase.master.AssignmentManager.assign(AssignmentManager.java:1338)
 at org.apache.hadoop.hbase.master.AssignmentManager.assign(AssignmentManager.java:1333)
 at org.apache.hadoop.hbase.master.AssignmentManager.assignRoot(AssignmentManager.java:2212)
 at org.apache.hadoop.hbase.master.HMaster.assignRootAndMeta(HMaster.java:632)
 at org.apache.hadoop.hbase.master.HMaster.finishInitialization(HMaster.java:529)
 at org.apache.hadoop.hbase.master.HMaster.run(HMaster.java:344)
 at org.apache.hadoop.hbase.master.HMasterCommandLine$LocalHMaster.run(HMasterCommandLine.java:220)
 at java.lang.Thread.run(Thread.java:679)
Caused by: java.net.ConnectException: Connection refused
 at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
 at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:592)
 at org.apache.hadoop.net.SocketIOWithTimeout.connect(SocketIOWithTimeout.java:206)
 at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:489)
 at org.apache.hadoop.hbase.ipc.HBaseClient$Connection.setupConnection(HBaseClient.java:416)
 at org.apache.hadoop.hbase.ipc.HBaseClient$Connection.setupIOstreams(HBaseClient.java:462)
 at org.apache.hadoop.hbase.ipc.HBaseClient.getConnection(HBaseClient.java:1150)
 at org.apache.hadoop.hbase.ipc.HBaseClient.call(HBaseClient.java:1000)
 at org.apache.hadoop.hbase.ipc.WritableRpcEngine$Invoker.invoke(WritableRpcEngine.java:150)
 at $Proxy12.getProtocolVersion(Unknown Source)
 at org.apache.hadoop.hbase.ipc.WritableRpcEngine.getProxy(WritableRpcEngine.java:183)
 at org.apache.hadoop.hbase.ipc.HBaseRPC.getProxy(HBaseRPC.java:335)
 at org.apache.hadoop.hbase.ipc.HBaseRPC.getProxy(HBaseRPC.java:312)
 at org.apache.hadoop.hbase.ipc.HBaseRPC.getProxy(HBaseRPC.java:364)
 at org.apache.hadoop.hbase.ipc.HBaseRPC.waitForProxy(HBaseRPC.java:236)
 ... 15 more
2012-11-20 09:29:08,476 WARN org.apache.hadoop.hbase.master.AssignmentManager: Unable to find a viable location to assign region -ROOT-,,0.70236052

The root cause of this issue resides in your /etc/hosts file. If you check your /etc/hosts file you will find a entry something like the one below (in my case mu machine is named APEX1)

127.0.0.1 localhost
127.0.1.1 apex1

# The following lines are desirable for IPv6 capable hosts
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

The root cause is that apex1 resolves to 127.0.1.1 which is incorrect as it should resolve to 127.0.0.1 (or a external IP). As my external IP is 192.168.58.10 I created the following /etc/hosts configuration;

127.0.0.1 localhost
192.168.58.10 apex1

# The following lines are desirable for IPv6 capable hosts
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

This will ensure that the resolving of your host processes on your localhost will be done correctly and you can start your HBase installation correctly on your development system.