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docs/reconcile_flow.md

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+# Harbor Cluster Reconciler
+
+## Control Loop
+
+ ![Control Loop](./assets/reconcile.png)
+
+### The Criterion of READY
+
+   The important point of Control Loop is how to evaluate the CRs(Redis, PostgreSql, Minio) status is READY.
+   When all of the three dependencies is READY, operator can create the Harbor CR.
+
+ - Redis
+
+    When the available replicas of redis is equal to `.spec.redis.replicas` in Redis CR. 
+    And the available replicas of redis sentinel is equal to `.spec.sentinel.replicas` is Redis CR.
+
+    And using `PING` command to check redis can be connected.
+
+ - PostgreSQL
+
+    In Postgres CR's status, there is string field named `PostgresClusterStatus`, which indicates whether the PostgreSQL services is Healthy.
+    In current stage, we directly use it to evaluate the PostgreSQL is ready when this field is equal to `running`.
+
+ - MinIO
+
+    In Minio CR's status, there is int32 field named `AvailableReplicas`, which indicates the available replicas of MinIO instance.
+    So, when `.status.availableReplicas` is equal to `.spec.replicas`, it is ready. 
+
+### Resource Status 
+
+```yaml
+status:
+  conditions:
+  - # type values may be Cache, Database, Storage, HarborCore  
+    type: Cache
+    # status values may be True, False, or Unknown. The absence of a condition should be interpreted the same as Unknown. How controllers handle Unknown depends on the Condition in question.
+    status: True
+    # optional
+    message: may contain specific details
+    # optional
+    lastTransitionTime: 2020-03-29T15:05:42Z
+
+```
+