Adds support for remote discovery to the destination controller.
When the destination controller gets a `Get` request for a Service with the `multicluster.linkerd.io/remote-discovery` label, this is an indication that the destination controller should discover the endpoints for this service from a remote cluster. The destination controller will look for a remote cluster which has been linked to it (using the `linkerd multicluster link` command) with that name. It will look at the `multicluster.linkerd.io/remote-discovery` label for the service name to look up in that cluster. It then streams back the endpoint data for that remote service.
Since we now have multiple client-go informers for the same resource types (one for the local cluster and one for each linked remote cluster) we add a `cluster` label onto the prometheus metrics for the informers and EndpointWatchers to ensure that each of these components' metrics are correctly tracked and don't overwrite each other.
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Signed-off-by: Alex Leong <alex@buoyant.io>
* Use metadata API in the proxy and tap injectors
Part of #9485
This adds a new `MetadataAPI` similar to the current `k8s.API` hosting informers, but backed by k8s' `metadatainformer` shared informers, which retrieves only the objects metadata, resulting in less memory consumption by its clients. Currently this is only implemented for the proxy and tap injectors. Usage by the destination controller will be implemented as a follow-up.
## Existing API enhancements
Shared objects and logic required by API and MetadataAPI have been moved to the new `k8s.go`, `api_resource.go` and `prometheus.go` files. That includes the `isValidRSParent()` function whose arg is now more generic.
## Unit tests
`/controller/k8s/api_test.go` now also instantiates a MetadataAPI, used in the augmented `TestGetObjects()` and `TestGetOwnerKindAndName()` tests. The `resources` struct was introduced to capture the common fields among tests and simplify `newMockAPI()`'s signature.
## Other Changes
The injector no longer watches for Pods. It only requires watching workloads that own resources (and also watch namespaces), so Pod is not required.
## Testing Memory Consumption
Install linkerd, inject emojivoto and check the injector memory consumption with `kubectl -n linkerd top pod linkerd-proxy-injector-xxx`. It'll start consuming about 16Mi. Then ramp up emojivoto's `voting` deployment replicas to 2000. After 5 minutes memory will stabilize around 32Mi using the current branch. Using the latest edge, it'll stabilize around 110Mi.
Alex Leong
Alejandro Pedraza