Load Sharing using IP Network Address Translation (RFC 2391, LSNAT).

LSNAT links are first created by either PacketAliasRedirectPort() or
PacketAliasRedirectAddress() and then set up by one or more calls to
PacketAliasAddServer().

1 files changed, 60 insertions, 0 deletions

diff --git a/lib/libalias/libalias.3 b/lib/libalias/libalias.3
index 42840af..36788d5 100644
--- a/lib/libalias/libalias.3
+++ b/lib/libalias/libalias.3
@@ -376,6 +376,14 @@ is called to change the address after
 .Fn PacketAliasRedirectPort
 is called, a zero reference will track this change.
 .Pp
+If the link is further set up to operate for a load sharing, then
+.Fa local_addr
+and
+.Fa local_port
+are ignored, and are selected dynamically from the server pool, as described in
+.Fn PacketAliasAddServer
+below.
+.Pp
 If
 .Fa remote_addr
 is zero, this indicates to redirect packets from any remote address.
@@ -434,6 +442,12 @@ is called to change the address after
 .Fn PacketAliasRedirectAddr
 is called, a zero reference will track this change.
 .Pp
+If the link is further set up to operate for a load sharing, then
+.Fa local_addr
+is ignored, and is selected dynamically from the server pool, as described in
+.Fn PacketAliasAddServer
+below.
+.Pp
 If subsequent calls to
 .Fn PacketAliasRedirectAddr
 use the same aliasing address, all new incoming traffic to this aliasing
@@ -471,6 +485,52 @@ If
 is returned, then the function call did not complete successfully.
 .Ed
 .Pp
+.Ft int
+.Fo PacketAliasAddServer
+.Fa "struct alias_link *link"
+.Fa "struct in_addr addr"
+.Fa "u_short port"
+.Fc
+.Bd -ragged -offset indent
+This function sets the
+.Fa link
+up for Load Sharing using IP Network Address Translation (RFC 2391, LSNAT).
+LSNAT operates as follows.
+A client attempts to access a server by using the server virtual address.
+The LSNAT router transparently redirects the request to one of the hosts
+in server pool, selected using a real-time load sharing algorithm.
+Multiple sessions may be initiated from the same client, and each session
+could be directed to a different host based on load balance across server
+pool hosts at the time.
+If load share is desired for just a few specific services, the configuration
+on LSNAT could be defined to restrict load share for just the services
+desired.
+.Pp
+Currently, only the simplest selection algorithm is implemented, where a
+host is selected on a round-robin basis only, without regard to load on
+the host.
+.Pp
+First, the
+.Fa link
+is created by either
+.Fn PacketAliasRedirectPort
+or
+.Fn PacketAliasRedirectAddr .
+Then,
+.Fn PacketAliasAddServer
+is called multiple times to add entries to the
+.Fa link Ns 's
+server pool.
+.Pp
+For links created with
+.Fn PacketAliasRedirectAddr ,
+the
+.Fa port
+argument is ignored and could have any value, e.g. htons(~0).
+.Pp
+This function returns 0 on success, -1 otherwise.
+.Ed
+.Pp
 .Ft void
 .Fn PacketAliasRedirectDelete "struct alias_link *link"
 .Bd -ragged -offset indent