doc: added did-you-know.md to document the less-known

behaviours and features of GlusterFS

Change-Id: Ibabc6398be9fb1c20127aaad2c51a629fed7c10b
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/9103
Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Reviewed-by: Lalatendu Mohanty <lmohanty@redhat.com>
Tested-by: Lalatendu Mohanty <lmohanty@redhat.com>

1 files changed, 36 insertions, 0 deletions

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+#Did you know?
+
+This document is an attempt to describe less-documented behaviours and features
+of GlusterFS that an admin always wanted to know but was too shy or busy to
+ask.
+
+## Trusted Volfiles
+
+Observant admins would have wondered why there are two similar volume files for
+every volume, namely trusted-<VOLNAME>-fuse.vol and <VOLNAME>-fuse.vol. To
+appreciate this one needs to know about the IP address/hostname based access
+restriction schemes available in GlusterFS. They are "auth-allow" and
+"auth-reject".  The "auth-allow" and "auth-reject" options take a comma
+separated list of IP addresses/hostnames as value. "auth-allow" allows access
+_only_ to clients running on machines whose IP address/hostname are on this
+list.  It is highly likely for an admin to configure the "auth-allow" option
+without including the list of nodes in the cluster. One would expect this to
+work.  Previously, in this configuration (internal) clients such as
+gluster-nfs, glustershd etc., running in the trusted storage pool, would be
+denied access to the volume.  This is undesirable and counter-intuitive. The
+work around was to add the IP address/hostnames of all the nodes in the trusted
+storage pool to the "auth-allow" list. This is bad for a reasonably large
+number of nodes. To fix this, an alternate authentication mechanism for nodes
+in the storage pool was introduced. Following is a brief explanation of how
+this works.
+
+The volume file with trusted prefix in its name (i.e trusted-volfile) has a
+username and password option in the client xlator. The trusted-volfile is used
+_only_ by mount processes running in the trusted storage pool (hence the name).
+The username and password, when present, allow "mount" (and other glusterfs)
+processes to access the brick processes even if the node they are running on is
+not explicitly added in "auth-allow" addresses. 'Regular' mount processes,
+running on nodes outside the trusted storage pool, use the non-trusted-volfile.
+The important thing to note is that "trusted" in this context only implied
+belonging to the trusted storage pool.
+