Added high level architecture diagram for ice-rest-catalog with etcd …

doc/.ice.yaml

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+uri: http://localhost:8181
+s3:
+  endpoint: http://localhost:9000
+  pathStyleAccess: true
+  accessKeyID: minio
+  secretAccessKey: minio123
+  region: us-east-1

doc/architecture.md

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+# ICE REST Catalog Architecture
+
+![ICE REST Catalog Architecture](ice-rest-catalog-architecture.drawio.png)
+
+## Components
+
+- **ice-rest-catalog**: Stateless REST API service (Kubernetes Deployment)
+- **etcd**: Distributed key-value store for catalog state (Kubernetes StatefulSet)
+- **Object Storage**: S3-compatible storage for data files
+- **Clients**: ClickHouse or other Iceberg-compatible engines
+
+## Design Principles
+
+### Stateless Catalog
+
+The `ice-rest-catalog` is completely stateless and deployed as a Kubernetes Deployment with multiple replicas. It can be scaled horizontally without coordination. The catalog does not store any state locally—all metadata is persisted in etcd.
+
+### State Management
+
+All catalog state (namespaces, tables, schemas, snapshots, etc.) is maintained in **etcd**, a distributed, consistent key-value store. Each etcd instance runs as a StatefulSet pod with persistent storage, ensuring data durability across restarts.
+
+### Service Discovery
+
+`ice-rest-catalog` uses **DNS+SRV** records to discover and connect to the etcd cluster.
+The catalog uses jetcd library to interact with etcd https://github.com/etcd-io/jetcd. 
+The etcd cluster can be accessed using dns+srv as it allows dynamic discovery of etcd endpoints without hardcoded addresses.
+
+### High Availability
+
+- Multiple `ice-rest-catalog` replicas behind a load balancer
+- etcd cluster.
+- Persistent volumes for etcd data
+- S3 for durable object storage