The NFS Gateway supports NFSv3 and allows HDFS to be mounted as part of the client's local file system. Currently NFS Gateway supports and enables the following usage patterns:
The NFS gateway machine needs the same thing to run an HDFS client like Hadoop JAR files, HADOOP_CONF directory. The NFS gateway can be on the same host as DataNode, NameNode, or any HDFS client.
The NFS-gateway uses proxy user to proxy all the users accessing the NFS mounts. In non-secure mode, the user running the gateway is the proxy user, while in secure mode the user in Kerberos keytab is the proxy user. Suppose the proxy user is 'nfsserver' and users belonging to the groups 'users-group1' and 'users-group2' use the NFS mounts, then in core-site.xml of the NameNode, the following two properities must be set and only NameNode needs restart after the configuration change (NOTE: replace the string 'nfsserver' with the proxy user name in your cluster):
<property> <name>hadoop.proxyuser.nfsserver.groups</name> <value>root,users-group1,users-group2</value> <description> The 'nfsserver' user is allowed to proxy all members of the 'users-group1' and 'users-group2' groups. Note that in most cases you will need to include the group "root" because the user "root" (which usually belonges to "root" group) will generally be the user that initially executes the mount on the NFS client system. Set this to '*' to allow nfsserver user to proxy any group. </description> </property>
<property> <name>hadoop.proxyuser.nfsserver.hosts</name> <value>nfs-client-host1.com</value> <description> This is the host where the nfs gateway is running. Set this to '*' to allow requests from any hosts to be proxied. </description> </property>
The above are the only required configuration for the NFS gateway in non-secure mode. For Kerberized hadoop clusters, the following configurations need to be added to hdfs-site.xml for the gateway (NOTE: replace string "nfsserver" with the proxy user name and ensure the user contained in the keytab is also the same proxy user):
<property> <name>nfs.keytab.file</name> <value>/etc/hadoop/conf/nfsserver.keytab</value> <!-- path to the nfs gateway keytab --> </property>
<property> <name>nfs.kerberos.principal</name> <value>nfsserver/_HOST@YOUR-REALM.COM</value> </property>
The rest of the NFS gateway configurations are optional for both secure and non-secure mode.
The AIX NFS client has a few known issues that prevent it from working correctly by default with the HDFS NFS Gateway. If you want to be able to access the HDFS NFS Gateway from AIX, you should set the following configuration setting to enable work-arounds for these issues:
<property> <name>nfs.aix.compatibility.mode.enabled</name> <value>true</value> </property>
Note that regular, non-AIX clients should NOT enable AIX compatibility mode. The work-arounds implemented by AIX compatibility mode effectively disable safeguards to ensure that listing of directory contents via NFS returns consistent results, and that all data sent to the NFS server can be assured to have been committed.
It's strongly recommended for the users to update a few configuration properties based on their use cases. All the following configuration properties can be added or updated in hdfs-site.xml.
<property> <name>dfs.namenode.accesstime.precision</name> <value>3600000</value> <description>The access time for HDFS file is precise upto this value. The default value is 1 hour. Setting a value of 0 disables access times for HDFS. </description> </property>
<property> <name>nfs.dump.dir</name> <value>/tmp/.hdfs-nfs</value> </property>
<property> <name>nfs.exports.allowed.hosts</name> <value>* rw</value> </property>
To change logging level:
To get more details of ONCRPC requests:
Three daemons are required to provide NFS service: rpcbind (or portmap), mountd and nfsd. The NFS gateway process has both nfsd and mountd. It shares the HDFS root "/" as the only export. It is recommended to use the portmap included in NFS gateway package. Even though NFS gateway works with portmap/rpcbind provide by most Linux distributions, the package included portmap is needed on some Linux systems such as REHL6.2 due to an rpcbind bug. More detailed discussions can be found in HDFS-4763.
service nfs stop service rpcbind stop
hdfs portmap OR hadoop-daemon.sh start portmap
No root privileges are required for this command. In non-secure mode, the NFS gateway should be started by the proxy user mentioned at the beginning of this user guide. While in secure mode, any user can start NFS gateway as long as the user has read access to the Kerberos keytab defined in "nfs.keytab.file".
hdfs nfs3 OR hadoop-daemon.sh start nfs3
Note, if the hadoop-daemon.sh script starts the NFS gateway, its log can be found in the hadoop log folder.
hadoop-daemon.sh stop nfs3 hadoop-daemon.sh stop portmap
Optionally, you can forgo running the Hadoop-provided portmap daemon and instead use the system portmap daemon on all operating systems if you start the NFS Gateway as root. This will allow the HDFS NFS Gateway to work around the aforementioned bug and still register using the system portmap daemon. To do so, just start the NFS gateway daemon as you normally would, but make sure to do so as the "root" user, and also set the "HADOOP_PRIVILEGED_NFS_USER" environment variable to an unprivileged user. In this mode the NFS Gateway will start as root to perform its initial registration with the system portmap, and then will drop privileges back to the user specified by the HADOOP_PRIVILEGED_NFS_USER afterward and for the rest of the duration of the lifetime of the NFS Gateway process. Note that if you choose this route, you should skip steps 1 and 2 above.
rpcinfo -p $nfs_server_ip
You should see output similar to the following:
program vers proto port 100005 1 tcp 4242 mountd 100005 2 udp 4242 mountd 100005 2 tcp 4242 mountd 100000 2 tcp 111 portmapper 100000 2 udp 111 portmapper 100005 3 udp 4242 mountd 100005 1 udp 4242 mountd 100003 3 tcp 2049 nfs 100005 3 tcp 4242 mountd
showmount -e $nfs_server_ip
You should see output similar to the following:
Exports list on $nfs_server_ip : / (everyone)
Currently NFS v3 only uses TCP as the transportation protocol. NLM is not supported so mount option "nolock" is needed. It's recommended to use hard mount. This is because, even after the client sends all data to NFS gateway, it may take NFS gateway some extra time to transfer data to HDFS when writes were reorderd by NFS client Kernel.
If soft mount has to be used, the user should give it a relatively long timeout (at least no less than the default timeout on the host) .
The users can mount the HDFS namespace as shown below:
mount -t nfs -o vers=3,proto=tcp,nolock,noacl $server:/ $mount_point
Then the users can access HDFS as part of the local file system except that, hard link and random write are not supported yet. To optimize the performance of large file I/O, one can increase the NFS transfer size(rsize and wsize) during mount. By default, NFS gateway supports 1MB as the maximum transfer size. For larger data transfer size, one needs to update "nfs.rtmax" and "nfs.rtmax" in hdfs-site.xml.
In environments where root access on client machines is not generally available, some measure of security can be obtained by ensuring that only NFS clients originating from privileged ports can connect to the NFS server. This feature is referred to as "port monitoring." This feature is not enabled by default in the HDFS NFS Gateway, but can be optionally enabled by setting the following config in hdfs-site.xml on the NFS Gateway machine:
<property> <name>nfs.port.monitoring.disabled</name> <value>false</value> </property>
NFS gateway in this release uses AUTH_UNIX style authentication. When the user on NFS client accesses the mount point, NFS client passes the UID to NFS gateway. NFS gateway does a lookup to find user name from the UID, and then passes the username to the HDFS along with the HDFS requests. For example, if the NFS client has current user as "admin", when the user accesses the mounted directory, NFS gateway will access HDFS as user "admin". To access HDFS as the user "hdfs", one needs to switch the current user to "hdfs" on the client system when accessing the mounted directory.
The system administrator must ensure that the user on NFS client host has the same name and UID as that on the NFS gateway host. This is usually not a problem if the same user management system (e.g., LDAP/NIS) is used to create and deploy users on HDFS nodes and NFS client node. In case the user account is created manually on different hosts, one might need to modify UID (e.g., do "usermod -u 123 myusername") on either NFS client or NFS gateway host in order to make it the same on both sides. More technical details of RPC AUTH_UNIX can be found in RPC specification.
Optionally, the system administrator can configure a custom static mapping file in the event one wishes to access the HDFS NFS Gateway from a system with a completely disparate set of UIDs/GIDs. By default this file is located at "/etc/nfs.map", but a custom location can be configured by setting the "static.id.mapping.file" property to the path of the static mapping file. The format of the static mapping file is similar to what is described in the exports(5) manual page, but roughly it is:
# Mapping for clients accessing the NFS gateway uid 10 100 # Map the remote UID 10 the local UID 100 gid 11 101 # Map the remote GID 11 to the local GID 101