Create /path/key if-and-only-if /path exists but key does not

[schmichael]

Current behavior

As of etcd 2.0.11 the following creates /path/key iff /path/key does not exist. However, it will create /path/key regardless of whether or not /path exists.

curl -XPUT localhost:2379/v2/keys/path/key?prevExist=false
{"action":"create","node":{"key":"/path/key","value":"","modifiedIndex":7,"createdIndex":7}}

Desired behavior

Have an option (recursive=false perhaps?) to cause PUTs to fail if the parent path component doesn't exist.

Workaround

Depending on your use case the following may be a sufficient workaround:

• PUT /path/key?prevExist=false
• GET /path
  • If /path's CreatedIndex == /path/key's CreatedIndex, then: DELETE /path?recursive=true

Obviously this method isn't an atomic operation, so it's not suitable for all cases the Desired Behavior above covers.

[barakmich]

More importantly, you might like the byte-keyspace (and atomic transactions!) of the v3 API which is underway. We're holding off on extending v2 -- but if there is a clear bug here (ie, the creation of the /path/key) but I think that's documented that way -- if it's unexpected behavior then feel free to reopen!

[schmichael]

Oops, I didn't mean to repoen this with an unrelated ticket in a totally different project! Sorry!

However:

I don't see Create/PUT's recursive behavior documented anywhere, and other operations with recursive abilities (e.g. GET/DELETE) have the recursive=... option to toggle the behavior.

So I'd say this is a documentation "bug" and a missing feature. v3's atomic transactions is definitely a solution though, so feel free to re-close.