-.TH HBAL 1 2009-03-22 htools "Ganeti H-tools"
+.TH HBAL 1 2009-03-23 htools "Ganeti H-tools"
.SH NAME
hbal \- Cluster balancer for Ganeti
.B "[-o]"
.BI "[-l" limit "]"
.BI "[-O" name... "]"
+.BI "[-e" score "]"
.BI "[-m " cluster "]"
.BI "[-n " nodes-file " ]"
.BI "[-i " instances-file "]"
failover/migrate and replace-disks such that we change one of the
instance nodes, and the other one remains (but possibly with changed
role, e.g. from primary it becomes secondary). The list is:
- - failover (f)
- - replace secondary (r)
- - replace primary, a composite move (f, r, f)
- - failover and replace secondary, also composite (f, r)
- - replace secondary and failover, also composite (r, f)
+.RS 4
+.TP 3
+\(em
+failover (f)
+.TP
+\(em
+replace secondary (r)
+.TP
+\(em
+replace primary, a composite move (f, r, f)
+.TP
+\(em
+failover and replace secondary, also composite (f, r)
+.TP
+\(em
+replace secondary and failover, also composite (r, f)
+.RE
We don't do the only remaining possibility of replacing both nodes
(r,f,r,f or the equivalent f,r,f,r) since these move needs an
As said before, the algorithm tries to minimise the cluster score at
each step. Currently this score is computed as a sum of the following
components:
- - coefficient of variance of the percent of free memory
- - coefficient of variance of the percent of reserved memory
- - coefficient of variance of the percent of free disk
- - percentage of nodes failing N+1 check
- - percentage of instances living (either as primary or secondary) on
- offline nodes
+.RS 4
+.TP 3
+\(em
+coefficient of variance of the percent of free memory
+.TP
+\(em
+coefficient of variance of the percent of reserved memory
+.TP
+\(em
+coefficient of variance of the percent of free disk
+.TP
+\(em
+percentage of nodes failing N+1 check
+.TP
+\(em
+percentage of instances living (either as primary or secondary) on
+offline nodes
+.RE
The free memory and free disk values help ensure that all nodes are
somewhat balanced in their resource usage. The reserved memory helps
instances the same size and spread across the nodes equally), all
values would be zero. This doesn't happen too often in practice :)
+.SS OFFLINE INSTANCES
+
+Since current Ganeti versions do not report the memory used by offline
+(down) instances, ignoring the run status of instances will cause
+wrong calculations. For this reason, the algorithm subtracts the
+memory size of down instances from the free node memory of their
+primary node, in effect simulating the startup of such instances.
+
.SS OTHER POSSIBLE METRICS
It would be desirable to add more metrics to the algorithm, especially
dynamically-computed metrics, such as:
- - CPU usage of instances, combined with VCPU versus PCPU count
- - Disk IO usage
- - Network IO
+.RS 4
+.TP 3
+\(em
+CPU usage of instances, combined with VCPU versus PCPU count
+.TP
+\(em
+Disk IO usage
+.TP
+\(em
+Network IO
+.RE
.SH OPTIONS
The options that can be passed to the program are as follows:
status.
The line will contain four fields:
- - initial cluster score
- - number of steps in the solution
- - final cluster score
- - improvement in the cluster score
+.RS
+.RS 4
+.TP 3
+\(em
+initial cluster score
+.TP
+\(em
+number of steps in the solution
+.TP
+\(em
+final cluster score
+.TP
+\(em
+improvement in the cluster score
+.RE
+.RE
.TP
.BI "-O " name
This option (which can be given multiple times) will mark nodes as
being \fIoffline\fR. This means a couple of things:
.RS
-.TP
--
+.RS 4
+.TP 3
+\(em
instances won't be placed on these nodes, not even temporarily;
e.g. the \fIreplace primary\fR move is not available if the secondary
node is offline, since this move requires a failover.
.TP
--
+\(em
these nodes will not be included in the score calculation (except for
the percentage of instances on offline nodes)
.RE
+.RE
+
+.TP
+.BI "-e" score ", --min-score=" score
+This parameter denotes the minimum score we are happy with and alters
+the computation in two ways:
+.RS
+.RS 4
+.TP 3
+\(em
+if the cluster has the initial score lower than this value, then we
+don't enter the algorithm at all, and exit with success
+.TP
+\(em
+during the iterative process, if we reach a score lower than this
+value, we exit the algorithm
+.RE
+The default value of the parameter is currently \fI1e-9\fR (chosen
+empirically).
+.RE
.TP
.BI "-n" nodefile ", --nodes=" nodefile
The name of the file holding node information (if not collecting via
-RAPI), instead of the default
-.I nodes
-file.
+RAPI), instead of the default \fInodes\fR file (but see below how to
+customize the default value via the environment).
.TP
.BI "-i" instancefile ", --instances=" instancefile
The name of the file holding instance information (if not collecting
-via RAPI), instead of the default
-.I instances
-file.
+via RAPI), instead of the default \fIinstances\fR file (but see below
+how to customize the default value via the environment).
.TP
.BI "-m" cluster
The exist status of the command will be zero, unless for some reason
the algorithm fatally failed (e.g. wrong node or instance data).
+.SH ENVIRONMENT
+
+If the variables \fBHTOOLS_NODES\fR and \fBHTOOLS_INSTANCES\fR are
+present in the environment, they will override the default names for
+the nodes and instances files. These will have of course no effect
+when RAPI is used.
+
.SH BUGS
The program does not check its input data for consistency, and aborts
The algorithm is not perfect.
+The algorithm doesn't deal with non-\fBdrbd\fR instances, and chokes
+on input data which has such instances.
+
The output format is not easily scriptable, and the program should
feed moves directly into Ganeti (either via RAPI or via a gnt-debug
input file).
projects / ganeti-local / blobdiff