docs(p7): add database connection strings for backend teams

Documents JDBC URLs, K8s Service endpoints, and secret reference
patterns for all three MySQL databases (customers, vets, visits).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: robeerah

docs/db-connection-strings.md

@@ -0,0 +1,155 @@
+# Database Connection Strings — P7 Database Administrator
+**Cluster:** petclinic-cluster | **Region:** us-east-1 | **Namespace:** spring-petclinic  
+**Verified:** 2026-05-14
+
+---
+
+## Secret (Credentials)
+
+All three databases share one Kubernetes Secret:
+
+```bash
+kubectl get secret petclinic-db-secret -n spring-petclinic
+```
+
+| Key | Description |
+|-----|-------------|
+| `mysql-user` | App username (`petclinic`) |
+| `mysql-password` | App user password |
+| `mysql-root-password` | Root password |
+
+Reference in your deployment YAML:
+```yaml
+env:
+  - name: SPRING_DATASOURCE_USERNAME
+    valueFrom:
+      secretKeyRef:
+        name: petclinic-db-secret
+        key: mysql-user
+  - name: SPRING_DATASOURCE_PASSWORD
+    valueFrom:
+      secretKeyRef:
+        name: petclinic-db-secret
+        key: mysql-password
+```
+
+---
+
+## customers-db — used by `customers-service` (P5)
+
+| Property | Value |
+|----------|-------|
+| Pod | `customers-db-mysql-0` |
+| Status | Running |
+| ClusterIP | `172.20.37.167` |
+| Pod IP | `10.0.3.76` |
+| Port | `3306` |
+
+**JDBC URL:**
+```
+jdbc:mysql://customers-db-mysql.spring-petclinic.svc.cluster.local:3306/petclinic
+```
+
+**Short form (within same namespace):**
+```
+jdbc:mysql://customers-db-mysql:3306/petclinic
+```
+
+**For `customers-service` deployment env:**
+```yaml
+- name: SPRING_DATASOURCE_URL
+  value: "jdbc:mysql://customers-db-mysql:3306/petclinic"
+- name: SPRING_PROFILES_ACTIVE
+  value: "docker,mysql"
+```
+
+---
+
+## vets-db — used by `vets-service` (P5)
+
+| Property | Value |
+|----------|-------|
+| Pod | `vets-db-mysql-0` |
+| Status | Running |
+| ClusterIP | `172.20.196.142` |
+| Pod IP | `10.0.3.211` |
+| Port | `3306` |
+
+**JDBC URL:**
+```
+jdbc:mysql://vets-db-mysql.spring-petclinic.svc.cluster.local:3306/petclinic
+```
+
+**Short form (within same namespace):**
+```
+jdbc:mysql://vets-db-mysql:3306/petclinic
+```
+
+**For `vets-service` deployment env:**
+```yaml
+- name: SPRING_DATASOURCE_URL
+  value: "jdbc:mysql://vets-db-mysql:3306/petclinic"
+- name: SPRING_PROFILES_ACTIVE
+  value: "docker,mysql"
+```
+
+---
+
+## visits-db — used by `visits-service` (P6)
+
+| Property | Value |
+|----------|-------|
+| Pod | `visits-db-mysql-0` |
+| Status | Running |
+| ClusterIP | `172.20.124.137` |
+| Pod IP | `10.0.3.135` |
+| Port | `3306` |
+
+**JDBC URL:**
+```
+jdbc:mysql://visits-db-mysql.spring-petclinic.svc.cluster.local:3306/petclinic
+```
+
+**Short form (within same namespace):**
+```
+jdbc:mysql://visits-db-mysql:3306/petclinic
+```
+
+**For `visits-service` deployment env:**
+```yaml
+- name: SPRING_DATASOURCE_URL
+  value: "jdbc:mysql://visits-db-mysql:3306/petclinic"
+- name: SPRING_PROFILES_ACTIVE
+  value: "docker,mysql"
+```
+
+---
+
+## Quick Connectivity Test Commands
+
+```bash
+# Test customers-db
+kubectl exec -i customers-db-mysql-0 -n spring-petclinic -- \
+  mysql -u petclinic -p<PASSWORD> petclinic -e "SELECT 'OK';"
+
+# Test vets-db
+kubectl exec -i vets-db-mysql-0 -n spring-petclinic -- \
+  mysql -u petclinic -p<PASSWORD> petclinic -e "SELECT 'OK';"
+
+# Test visits-db
+kubectl exec -i visits-db-mysql-0 -n spring-petclinic -- \
+  mysql -u petclinic -p<PASSWORD> petclinic -e "SELECT 'OK';"
+
+# Get the password from the secret
+kubectl get secret petclinic-db-secret -n spring-petclinic \
+  -o jsonpath='{.data.mysql-password}' | base64 --decode
+```
+
+---
+
+## Notes for P5 and P6
+
+- Databases are ready — **no manual schema setup needed.** Spring Boot auto-runs `schema.sql` and `data.sql` on first startup when `mysql` profile is active.
+- Always use the **Service DNS name** (e.g., `customers-db-mysql`), not the pod IP — pod IPs change on restart.
+- All databases are `ClusterIP` (internal only) — not reachable from outside the cluster.
+- Secret `petclinic-db-secret` already exists in the `spring-petclinic` namespace — just reference it in your deployment YAML.