Revision 73b2e389 hbal.1
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is O(n*n) in the number of nodes. Furthermore, it doesn't seems to |
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give better scores but will result in more disk replacements. |
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.SS PLACEMENT RESTRICTIONS |
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At each step, we prevent an instance move if it would cause: |
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.RS 4 |
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.TP 3 |
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\(em |
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a node to go into N+1 failure state |
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.TP |
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\(em |
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an instance to move onto an offline node (offline nodes are either |
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read from the cluster or declared with \fI-O\fR) |
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.TP |
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\(em |
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an exclusion-tag based conflict (exclusion tags are read from the |
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cluster and/or defined via the \fI--exclusion-tags\fR option) |
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.TP |
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\(em |
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a max vcpu/pcpu ratio to be exceeded (configured via \fI--max-cpu\fR) |
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.TP |
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\(em |
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min disk free percentage to go below the configured limit (configured |
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via \fI--min-disk\fR) |
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.SS CLUSTER SCORING |
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As said before, the algorithm tries to minimise the cluster score at |
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memory size of down instances from the free node memory of their |
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primary node, in effect simulating the startup of such instances. |
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.SS OTHER POSSIBLE METRICS |
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.SS EXCLUSION TAGS |
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The exclusion tags mecanism is designed to prevent instances which run |
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the same workload (e.g. two DNS servers) to land on the same node, |
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which would make the respective node a SPOF for the given service. |
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It works by tagging instances with certain tags and then building |
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exclusion maps based on these. Which tags are actually used is |
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configured either via the command line (option \fI--exclusion-tags\fR) |
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or via adding them to the cluster tags: |
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It would be desirable to add more metrics to the algorithm, especially |
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dynamically\(hycomputed metrics, such as: |
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.RS 4 |
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.TP 3 |
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\(em |
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CPU usage of instances |
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.TP |
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\(em |
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Disk IO usage |
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.B --exclusion-tags=a,b |
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This will make all instance tags of the form \fIa:*\fR, \fIb:*\fR be |
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considered for the exclusion map |
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.TP |
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\(em |
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Network IO |
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.RE |
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cluster tags \fBhtools:iextags:a\fR, \fBhtools:iextags:b\fR |
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This will make instance tags \fIa:*\fR, \fIb:*\fR be considered for |
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the exclusion map. More precisely, the suffix of cluster tags starting |
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with \fBhtools:iextags:\fR will become the prefix of the exclusion |
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tags. |
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.P |
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Both the above forms mean that two instances both having (e.g.) the |
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tag \fIa:foo\fR or \fIb:bar\fR won't end on the same node. |
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.SH OPTIONS |
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The options that can be passed to the program are as follows: |
Also available in: Unified diff