WebDAV stands for Distributed Authoring and Versioning. It is a set of extensions to the HTTP protocol that lets users collaboratively edit and manage files on a remote web server. It is often considered as a replacement for NFS or SAMBA
HDFS (Hadoop Distributed File System) needs a friendly file system interface. DFSShell commands are unfamiliar. Instead it is more convenient for Hadoop users to use a mountable network drive. A friendly interface to HDFS will be used both for casual browsing of data and for bulk import/export.
The FUSE provider for HDFS is already available ( http://issues.apache.org/jira/browse/HADOOP-17
) but it had scalability problems. WebDAV is a popular alternative.
The typical licensing terms for WebDAV tools are also attractive:
GPL for Linux client tools that Hadoop would not redistribute anyway.
More importantly, Apache Project/Apache license for Java tools and for server components.
This allows for a tighter integration with the HDFS code base.
There are some interesting Apache projects that support WebDAV.
But these are probably too heavyweight for the needs of Hadoop:
Tomcat servlet: http://tomcat.apache.org/tomcat-4.1-doc/catalina/docs/api/org/apache/catalina/servlets/WebdavServlet.html
Slide: http://jakarta.apache.org/slide/
Being HTTP-based and "backwards-compatible" with Web Browser clients, the WebDAV server protocol could even be piggy-backed on the existing Web UI ports of the Hadoop name node / data nodes. WebDAV can be hosted as (Jetty) servlets. This minimizes server code bloat and this avoids additional network traffic between HDFS and the WebDAV server.
General Clients (read-only):
Any web browser
Linux Clients:
Mountable GPL davfs2 http://dav.sourceforge.net/
FTP-like GPL Cadaver http://www.webdav.org/cadaver/
Server Protocol compliance tests:
http://www.webdav.org/neon/litmus/
A goal is for Hadoop HDFS to pass this test (minus support for Properties)
Pure Java clients:
DAV Explorer Apache lic. http://www.ics.uci.edu/~webdav/
WebDAV also makes it convenient to add advanced features in an incremental fashion:
file locking, access control lists, hard links, symbolic links.
New WebDAV standards get accepted and more or less featured WebDAV clients exist.
core http://www.webdav.org/specs/rfc2518.html
ACLs http://www.webdav.org/specs/rfc3744.html
redirects "soft links" http://greenbytes.de/tech/webdav/rfc4437.html
BIND "hard links" http://www.webdav.org/bind/
quota http://tools.ietf.org/html/rfc4331
New Feature
Open
Major
Expose HDFS as a WebDAV store
