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[vpc, enhancement] Allow starcluster to choose subnet automatically based on desired zone #390

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nitecoder opened this Issue Apr 9, 2014 · 0 comments

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Non-VPC clusters support having nodes and master reside in different availability zones. If one is mounting EBS volumes, the master has to be in the same zone as the volumes, but otherwise the nodes can be in any zone. This is very useful, especially when a spot price in one zone moves too high but other zones are available for much less.

Unfortunately, VPC clusters don't function the same way. Subnets are zone-specific and once a subnet is specified in the cluster settings it can't be changed. Addnode command currently does not accept a subnet override.

Minimal Change

  • Add -N option to addnode command to specify a different subnet. Users will need to ensure that the subnet is in the zone they are requesting and that it is in the right VPC and has IPs available.

A Cadillac Version
Let StarCluster pick the subnet to use automatically by examining the available subnets for a given VPC (or from a list specified by the user).

  • Also allow user to specify only the VPC_ID and obtain the list of subnets automatically
  • Allow user to specify a list of subnets in the config instead of just one
  • From the list of subnets, find the ones in the desired zone and having available IPs.

Support some simple rules to reduce changes of nodes of the same cluster being in different subnets, unless there is a good reason for it.

  • If zone is not specifically requested, default to the one specified in the cluster config
  • If multiple subnets are available and have IPs, prefer the one where the master or other nodes are already allocated
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