[Feature] Enhanced horizontal scaling of app controller

[fourierr]

Is your feature request related to a problem? Please describe.
Due to the leader-election of the controller, when there are thousands of application CRs in the hubcluster,
the new application will be delayed for updating longer and longer time.

Describe the solution you'd like
For this issue, i have made some experimental solution.
We want to dispatch several deployment of app controller in hubcluster.
Firstly, enabling the leader election and set leader-election-resource-name with different name e.g sharding-1, sharding-2.
Secondly, we add a label tag for every application CR, e.g app.oam.dev/sharding=sharding-1
Thirdly, add a filter to controller's eventFilter. Only the value of label tag is equal to leader-election-resource-name, the controller will handle the application CR.

The final effect is: application CR with label value of sharding-1 will only be processed by app controller with leader-selection-resource-name value of sharding-1

[Somefive]

Great! This solution looks good and is similar to what I have been thinking for sharding. Would you like to make a PR for that?

[fourierr]

Great! This solution looks good and is similar to what I have been thinking for sharding. Would you like to make a PR for that?

Of course, i will make a PR.

[wonderflow]

lgtm

[wonderflow]

Just FYI, there's another solution for this issue, which don't need change the controller code: https://github.com/openkruise/controllermesh

[wonderflow]

Sharding is supported now, please check #5360

It will be released in 1.8.0 and you can already enjoy this feature in https://github.com/kubevela/kubevela/releases/tag/v1.8.0-alpha.1

Closing