### What
`GetProfile` clients do not receive destinatin profiles that consider Server protocol fields the way that `Get` clients do. If a Server exists for a `GetProfile` destination that specifies the protocol for that destination is `opaque`, this information is not passed back to the client.
#7184 added this for `Get` by subscribing clients to Endpoint/EndpointSlice updates. When there is an update, or there is a Server update, the endpoints watcher passes this information back to the endpoint translator which handles sending the update back to the client.
For `GetProfile` the situation is different. As with `Get`, we only consider Servers when dealing with Pod IPs, but this only occurs in two situations for `GetProfile`.
1. The destination is a Pod IP and port
2. The destionation is an Instance ID and port
In both of these cases, we need to check if a already Server selects the endpoint and we need to subscribe for Server updates incase one is added or deleted which selects the endpoint.
### How
First we check if there is already a Server which selects the endpoint. This is so that when the first destionation profile is returned, the client knows if the destination is `opaque` or not.
After sending that first update, we then subscribe the client for any future updates which will come from a Server being added or deleted.
This is handled by the new `ServerWatcher` which watches for Server updates on the cluster; when an update occurs it sends that to the `endpointProfileTranslator` which translates the protcol update into a DestinationProfile.
By introducing the `endpointProfileTranslator` which only handles protocol updates, we're able to decouple the endpoint logic from `profileTranslator`—it's `endpoint` field has been removed now that it only handles updates for ServiceProfiles for Services.
### Testing
A unit test has been added and below are some manual testing instructions to see how it interacts with Server updates:
<details>
<summary>app.yaml</summary>
```yaml
apiVersion: v1
kind: Pod
metadata:
name: pod
labels:
app: pod
spec:
containers:
- name: app
image: nginx
ports:
- name: http
containerPort: 80
---
apiVersion: policy.linkerd.io/v1beta1
kind: Server
metadata:
name: srv
labels:
policy: srv
spec:
podSelector:
matchLabels:
app: pod
port: 80
proxyProtocol: opaque
```
</details>
```shell
$ go run ./controller/cmd/main.go destination
```
```shell
$ linkerd inject app.yaml |kubectl apply -f -
...
$ kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
pod 2/2 Running 0 53m 10.42.0.34 k3d-k3s-default-server-0 <none> <none>
$ go run ./controller/script/destination-client/main.go -method getProfile -path 10.42.0.34:80
...
```
You can add/delete `srv` as well as edit its `proxyProtocol` field to observe the correct DestinationProfile updates.
Signed-off-by: Kevin Leimkuhler <kleimkuhler@icloud.com>
Kevin Leimkuhler