I have couple of questions regarding the configMap versioning.
Is it possible to use a specific version of a configMap in the deployment file?
I dont see any API's to get list of versions. How to get the list of versions?
Is it possible to compare configMap b/w versions?
Thanks
Is it possible to use a specific version of a configMap in the deployment file?
Not really.
The closest notion of a "version" is resourceVersion, but that is not for the user to directly act upon.
See API conventions: concurrency control and consistency:
Kubernetes leverages the concept of resource versions to achieve optimistic concurrency. All Kubernetes resources have a "
resourceVersion" field as part of their metadata. ThisresourceVersionis a string that identifies the internal version of an object that can be used by clients to determine when objects have changed.
When a record is about to be updated, it's version is checked against a pre-saved value, and if it doesn't match, the update fails with aStatusConflict(HTTP status code 409).The
resourceVersionis changed by the server every time an object is modified. IfresourceVersionis included with thePUToperation the system will verify that there have not been other successful mutations to the resource during a read/modify/write cycle, by verifying that the current value ofresourceVersionmatches the specified value.The
resourceVersionis currently backed by etcd'smodifiedIndex.
However, it's important to note that the application should not rely on the implementation details of the versioning system maintained by Kubernetes. We may change the implementation ofresourceVersionin the future, such as to change it to a timestamp or per-object counter.The only way for a client to know the expected value of
resourceVersionis to have received it from the server in response to a prior operation, typically aGET. This value MUST be treated as opaque by clients and passed unmodified back to the server.
Clients should not assume that the resource version has meaning across namespaces, different kinds of resources, or different servers.
Currently, the value ofresourceVersionis set to match etcd's sequencer. You could think of it as a logical clock the API server can use to order requests. However, we expect the implementation ofresourceVersionto change in the future, such as in the case we shard the state by kind and/or namespace, or port to another storage system.In the case of a conflict, the correct client action at this point is to
GETthe resource again, apply the changes afresh, and try submitting again.
This mechanism can be used to prevent races like the following:
Client #1 Client #2
GET Foo GET Foo
Set Foo.Bar = "one" Set Foo.Baz = "two"
PUT Foo PUT Foo
When these sequences occur in parallel, either the change to
Foo.Baror the change toFoo.Bazcan be lost.On the other hand, when specifying the
resourceVersion, one of thePUTs will fail, since whichever write succeeds changes theresourceVersionforFoo.
resourceVersionmay be used as a precondition for other operations (e.g.,GET,DELETE) in the future, such as for read-after-write consistency in the presence of caching."Watch" operations specify
resourceVersionusing a query parameter. It is used to specify the point at which to begin watching the specified resources.
This may be used to ensure that no mutations are missed between aGETof a resource (or list of resources) and a subsequent Watch, even if the current version of the resource is more recent.
This is currently the main reason that list operations (GETon a collection) returnresourceVersion.