add logging dev guides

Signed-off-by: huanggze <loganhuang@yunify.com>

docs/en/guides/README.md

@@ -68,7 +68,9 @@ TODO(@huanggze)
 
 ### KubeSphere Logging developer
 
-TODO(@huanggze)
+1. Read kubesphere's [Concepts And Designs for Logging](../concepts-and-designs/kubesphere-logging.md). Understand KubeSphere's logging stack.
+2. Find the component you are interested in and start from its own repo: [Fluent Bit](https://github.com/kubesphere/fluent-bit), [Fluent-bit Operator](https://github.com/kubesphere/fluentbit-operator) and [Logsidecar Injector](https://github.com/kubesphere/logsidecar-injector).
+3. For developers who are interested in KubeSphere logging backend, read [Development Guide for Logging](kubesphere-logging-devlopment-guide.md) and [API doc](https://kubesphere.com.cn/docs/v2.1/api/kubesphere#tag/Log-Query).
 
 ### KubeSphere Altering developer
 

docs/en/guides/kubesphere-logging-devlopment-guide.md

@@ -0,0 +1,60 @@
+# Logging
+
+This documentation contains backend development guides for interaction with key components behind KubeSphere logging system. Logging backend provides the capabilities of:
+ 
+ - Log search
+ - Log export
+ - Log output configuration
+ - Multi-tenant isolation
+
+## File Tree
+
+The listing below covers all folders related to the logging backend.
+
+```
+/pkg
+  ├─api
+  │  └─logging            # declares structs for api responses
+  │     └─v1alpha2             
+  ├─apiserver             # implements handler for http requests
+  │  ├─logging            
+  │  └─tenant
+  ├─kapis                 # registers APIs and routing
+  │  ├─logging
+  │  │  ├─install
+  │  │  └─v1alpha2
+  │  ├─tenant
+  │  │  ├─install
+  │  │  └─v1alpha2
+  ├─models                
+  │  ├─log                # constants, utils and fluent-bit crd operation
+  │  │  ├─constants.go
+  │  │  ├─logcollector.go # some utils
+  │  │  ├─logcrd.go       # interacts with fluent-bit crd
+  │  │  └─types.go
+  │  └─tenant
+  └─simple
+     ├─factory.go         # contains factory functions for es client options
+     └─client
+        ├─elasticsearch   # wraps es search apis
+        │  ├─esclient.go  # constructs es search body 
+        │  ├─interface.go # general interface methods for es clients
+        │  ├─options.go   # es client options
+        │  └─versions     # client code by es versions
+        │     ├─v5
+        │     ├─v6
+        │     └─v7
+        └─fluentbit       # autogenerated client code for fluent-bit crd
+```
+
+## API Design
+
+There are two types of APIs in logging. One for log query, and the other for interacting with the CustomResourceDefinition used by [Fluent-bit Operator](https://github.com/kubesphere/fluentbit-operator). For information about CRD and Fluent-bit Operator, please go to its own repo.
+ 
+To support multi-tenant isolation, KubeSphere's logging query APIs have the format like below, though the underlying logic is using Elastic Search APIs:
+  
+```
+GET /namespaces/{namespace}/pods/{pod}/containers/{container}
+```
+
+KubeSphere API gateway will decode the URL and conduct authorization. A person who doesn't belong to a namespace will be rejected to make a request.