Blog: using ETCD as app DB (#2666)

Signed-off-by: Andrea Peruffo <andrea.peruffo1982@gmail.com>

docs/content/en/blog/news/etcd-as-app-db.md

@@ -0,0 +1,115 @@
+---
+title: Using k8s' ETCD as your application DB
+date: 2025-01-16
+---
+
+# FAQ: Is Kubernetes’ ETCD the Right Database for My Application?
+
+## Answer
+
+While the idea of moving your application data to Custom Resources (CRs) aligns with the "Cloud Native" philosophy, it often introduces more challenges than benefits. Let’s break it down:
+
+---
+
+### Top Reasons Why Storing Data in ETCD Through CRs Looks Appealing
+
+1. **Storing application data as CRs enables treating your application’s data like infrastructure:**
+   - **GitOps compatibility:** Declarative content can be stored in Git repositories, ensuring reproducibility.
+   - **Infrastructure alignment:** Application data can follow the same workflow as other infrastructure components.
+
+---
+
+### Challenges of Using Kubernetes’ ETCD as Your Application’s Database
+
+#### Technical Limitations:
+
+- **Data Size Limitations 🔴:**
+  - Each CR is capped at 1.5 MB by default. Raising this limit is possible but impacts cluster performance.
+  - Kubernetes ETCD has a storage cap of 2 GB by default. Adjusting this limit affects the cluster globally, with potential performance degradation.
+
+- **API Server Load Considerations 🟡:**
+  - The Kubernetes API server is designed to handle infrastructure-level requests.
+  - Storing application data in CRs might add significant load to the API server, requiring it to be scaled appropriately to handle both infrastructure and application demands.
+  - This added load can impact cluster performance and increase operational complexity.
+
+- **Guarantees 🟡:**
+  - Efficient queries are hard to implement and there is no support for them.
+  - ACID properties are challenging to leverage and everything holds mostly in read-only mode.
+
+#### Operational Impact:
+
+- **Lost Flexibility 🟡:**
+  - Modifying application data requires complex YAML editing and full redeployment.
+  - This contrasts with traditional databases that often feature user-friendly web UIs or APIs for real-time updates.
+
+- **Infrastructure Complexity 🟠:**
+  - Backup, restore, and lifecycle management for application data are typically separate from deployment workflows.
+  - Storing both in ETCD mixes these concerns, complicating operations and standardization.
+
+#### Security:
+
+- **Governance and Security 🔴:**
+  - Sensitive data stored in plain YAML may lack adequate encryption or access controls.
+  - Applying governance policies over text-based files can become a significant challenge.
+
+---
+
+### When Might Using CRs Make Sense?
+
+For small, safe subsets of data—such as application configurations—using CRs might be appropriate. However, this approach requires a detailed evaluation of the trade-offs.
+
+---
+
+### Conclusion
+
+While it’s tempting to unify application data with infrastructure control via CRs, this introduces risks that can outweigh the benefits. For most applications, separating concerns by using a dedicated database is the more robust, scalable, and manageable solution.
+
+---
+
+### A Practical Example
+
+A typical “user” described in JSON:
+
+```json
+{
+  "username": "myname",
+  "enabled": true,
+  "email": "myname@test.com",
+  "firstName": "MyFirstName",
+  "lastName": "MyLastName",
+  "credentials": [
+    {
+      "type": "password",
+      "value": "test"
+    },
+    {
+      "type": "token",
+      "value": "oidc"
+    }
+  ],
+  "realmRoles": [
+    "user",
+    "viewer",
+    "admin"
+  ],
+  "clientRoles": {
+    "account": [
+      "view-profile",
+      "change-group",
+      "manage-account"
+    ]
+  }
+}
+```
+
+This example represents about **0.5 KB of data**, meaning (with standard settings) a maximum of ~2000 users can be defined in the same CR.
+Additionally:
+
+- It contains **sensitive information**, which should be securely stored.
+- Regulatory rules (like GDPR) apply.
+
+---
+
+### References
+
+- [Using etcd as primary store database](https://stackoverflow.com/questions/41063238/using-etcd-as-primary-store-database)