fix: Use FQDN for backend service to avoid DNS search domain issues

[jelipo]

Problem

Loki init containers fail to resolve Kubernetes service DNS on Alpine Linux (musl libc):

Symptoms

Waiting for index gateway ring to be ready...
Backend service: logs-775b7c67d9-backend.kb-system.svc.cluster.local:3100
Max wait time: 300 seconds
Waiting for index gateway ring... (0/300 seconds)
Waiting for index gateway ring... (5/300 seconds)
Waiting for index gateway ring... (10/300 seconds)
Waiting for index gateway ring... (15/300 seconds)
Waiting for index gateway ring... (20/300 seconds)
Waiting for index gateway ring... (25/300 seconds)
Waiting for index gateway ring... (30/300 seconds)
Waiting for index gateway ring... (35/300 seconds)
Waiting for index gateway ring... (40/300 seconds)

me@k8s-master:~$ kubectl exec -it   logs-775b7c67d9-read-0 -n kb-system -c wait-index-gateway -- sh
/ # curl logs-775b7c67d9-backend.kb-system.svc.cluster.local:3100/ready
curl: (6) Could not resolve host: logs-775b7c67d9-backend.kb-system.svc.cluster.local

Reproduction

Tested on two different Kubernetes clusters with the same issue:

1. k3d cluster (v1.31.5+k3s1)
2. kubeadm cluster (v1.35.2)
   Both clusters exhibited the same DNS resolution failure in Alpine-based init containers.

Solution

Append a trailing dot (.) to service DNS names to use Fully Qualified Domain Names (FQDNs):

me@k8s-master:~$ kubectl exec -it   logs-775b7c67d9-read-0 -n kb-system -c wait-index-gateway -- sh
/ # curl logs-775b7c67d9-backend.kb-system.svc.cluster.local:3100/ready
curl: (6) Could not resolve host: logs-775b7c67d9-backend.kb-system.svc.cluster.local
/ # curl logs-775b7c67d9-backend.kb-system.svc.cluster.local.:3100/ready
ready

[heng4fun]

LGTM

[apecloud-bot]

/cherry-pick release-1.1

[apecloud-bot]

/cherry-pick release-1.0

[apecloud-bot]

🤖 says: cherry pick action finished successfully 🎉!
See: https://github.com/apecloud/kubeblocks-addons/actions/runs/22852603669

[apecloud-bot]

🤖 says: cherry pick action finished successfully 🎉!
See: https://github.com/apecloud/kubeblocks-addons/actions/runs/22852602548