Locking to avoid multiple like resources being created concurrently?

[OJFord]

Due to API deficiency, one of my resources needs to diff a list of remote resources of its kind either side of create, in order to determine its own identity.

As a result, adding two new terraform resources of this type at the same time results in my ‘expected one but found two’ error. The error’s designed to guard against extra-terraform changes, but I can’t just remove and ignore the issue, since if the diff has size two I don’t know which to assign to the created (terraform) resource.

Is there any way of locking around resource CRUD functions, (specifically or provider-wide) to ensure that they’re not invoked for different resources concurrently?

[kpfleming]

Handing Resource Count?

It will happen in parallel unless the ‘parallelism’ setting in Terraform is set to ‘1’ (it defaults to ‘10’). If the API operations to your IPAM are not atomic, then you’ll probably have to implement some sort of synchronization inside the provider to ensure that there is only one request active at a time. A sync.Mutex would be straightforward to use for this.

[OJFord]

@OJFord

FYI mutexkv is gone from recent versions of the v2 SDK, so the way to do it is:

import (
    "sync"
)

var myMutex  sync.Mutex

func foobar() {
    myMutex.Lock()
    // ...
    myMutex.Unlock()
}

Actually, all mutexkv was was a handy wapper around that to provide a map of multiple sync.Mutex s behind a string key. So, useful maybe, but not necessary and easily replicable. (Presumably that’s why it was removed!)

Unfortunately it was only after I’d worked this out that I discovered the third-party API I was using had changed, and I no longer need it, but maybe it’ll help someone else, or future me!

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