From: Maglinger, Paul (PMAGLINGER@scvl.com)
Date: Fri Nov 08 2002 - 17:46:24 EST
Original question was what determines which node you are directed to when
you login using the cluster name or IP? Running Tru64 5.1a?
My thanks to Dr. Tom Blinn, Mandell Degerness, Thomas Sjolshagen, and Lawrie
Smith whose responses gave me plenty of information and are listed below:
Dr. Tom - There is a load balancing algorithm that determines which node in
the
cluster is accepting new network connections. In most cases, it will
look a lot like random chance. There should be a description of this
in something like the cluster admin manual or the available apps book.
Mandell Degerness - All cluster services (including IP aliases) are assigned
to one and only one
node at a given time. You log in to the node which has that service
assigned to it. For instance, if you have a test_db service which includes
two volumes, an Oracle instance, and an IP address, that service can only be
assigned to a single node at a given time. When you connect to the
associated IP address, you are connected to the node running the test_db
service.
Thomas Sjolshagen - The node selection for the cluster alias on V5 clusters
is round-robin combined with the selection priority (selp) and selection
weight (selw) parameters (can be set using cluamgr). Normally, for the
default Cluster ALias, selw=3 and selp=3 (for all nodes) meaning that all of
the nodes are considered "equal" - as defined by the selp parameter (higher
= more important/more capable of handing connections - ie the one with the
highest selection priority handle more connections than any other) by the
Cluster Alias (this isn't something you're likely to play much with (unless
there's a node you want to only be a backup for a cluster alias - ie it's
only used if the guys w/a higher selp aren't "there"). The selw param
determines the number of connections to accept on the node before moving to
the next node w/the same or higher selp setting). So, which node gets what
connection is determined by the selw and selp.
Lawrie Smith - I think you need to look at the "selp" and "selw" settings
for your cluster
alias.
The default cluster alias is configured at cluster creation time. You can
use
# cluamgr -s DEFAULTALIAS
to display the default cluster alias configuration settings and statistics.
By default each member has the following alias characteristics
selw=3, selp=1, rpri=1 flags=11<JOINED,ENABLED>
If you create additional alias addresses then you can manipulate these
settings.
Selection priority: (selp) Creates logical subsets of aliases within an
alias. You can use selection priority to control which members of an alias
normally service requests. As long as those members with the highest
selection priority are up, members with a lower selection priority are not
given any requests. You can think of selection priority as a way to
establish a failover order for the members of an alias.
Selection weight: (selw) For in_multi services, provides static load
balancing among members of an alias. It provides a simple, method for
controlling which members of an alias get the most connections. The
selection weight indicates the number of connections (on average) that a
member is given before connections are given to the next alias member with
the same selection priority.
Our glory is not in never falling, but rising every time we fall.
Paul Maglinger, A+, CA, CCA, CET, MCSE
Systems Administrator Shoe Carnival Inc. (812)867-4674 pmaglinger@scvl.com
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