I am bit struggling to understand this Azure ARM template containing multiple "Microsoft.Compute/virtualMachines/extensions" and multiple VMs:

kafka-on-ubuntu/azuredeploy.json

Assuming there will be 4 VMs: 1 for zookeeper and 3 for Kafka cluster repsectively, how can be ensured that the extension ( script) for Zookeper will run on exactly that one Zookeper VM, and how to ensure that the extension ( script ) for Kafka cluster will run on exactly those 3 Kafka VMs? I am more tempted to believe that each extension run on all VMs.

CodePudding user response：

This behavior seems to be poorly documented, but from the documentation page for the Windows custom script extension:

The name of the resource has to be in the format virtualMachineName/extensionName, if this extension is used as a standalone resource in the Azure Resource Manager template.

Which seems to imply that the resolution for where the custom script extension should be executed is based on the name. I imagine this is the case for Linux VMs too.

For the particular example that you are looking at, the name of one of the vms is:

"name": "[concat('zookprvm', copyindex())]",

whereas that of the extension is:

"name": "[concat('zookprvm', copyindex(), '/installzoo')]",

so the prefix of the name of the extension must be identical to the VM name.