[KubernetesDiscoveryClient] Support cluster-ip as service-instance about micronaut-kubernetes HOT 11 CLOSED

Probably doable

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To be precise, what the current implementation uses is the EndpointsSubset.addresses. Quoting Kubernetes documentation:

IP addresses which offer the related ports that are marked as ready. These endpoints should be considered safe for load balancers and clients to utilize

The reason to not use the Service.clusterIP is consistency: all Micronaut service discovery implementations use Micronaut's load balancing capabilities.

So in this case, the issue is really an outdated service list, and therefore, implementing #186 by watching endpoints changes will fix this issue.

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@alvarosanchez We did not have caching enabled when we encountered the problem with unavailable pods in the service list. So from what I understand the discovery-client refreshed the service list on each request. One pod was unavailable nonetheless. Maybe the k8s api server state was not propagated fast enough, I dont know.
At the same time we had Micronaut 1.2.x-based apps that used the same service (with a failing pod) via the cluster-ip, and those apps experienced much fewer issues. 15 instances of 1.2-based apps had about 500 connection errors in total, at the same time a single 2.0.2 based canary app had connection 2000 errors. The traffic was evenly distributed over those 16 instances.

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If you really want to use the cluster IP, you can use the records created by kube-dns, eg:

@Client("my-service.my-namespace.svc.cluster.local")

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@alvarosanchez maybe worth documenting that somewhere if that is viable fix. @luckyswede does that work for you?

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also does that need to be in ${..}?

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Yes, we're going for a similar solution, we've implemented a discovery-client that creates a k8s service-url from the service-id. It's more "plug-n-play", we dont have to change the client annotations or add config entries.

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@graemerocher a related question, what is the contract for DiscoveryClient.getServiceIds? Is it supposed to return all service-ids that it has "seen" in requests to getInstances? Or a list of all service-ids it supports (which is not possible if the service-instance is calculated from the service-id)?

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also does that need to be in ${..}?

No, it doesn't. Given a service my-service in a namespace my-namespace, my-service.my-namespace.svc.cluster.local will be a DNS A record that will resolve to the service cluster IP.

But I did miss the rest of the URL, so it should be something like:

@Client("http://my-service.my-namespace.svc.cluster.local:8080")

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This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

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addressed in #215

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