Add Docker to Host communication Design document

doc/mgmt/Docker to Host communication.md

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+# Feature Name
+Docker to Host communication
+
+# High Level Design Document
+#### Rev 0.1
+
+# Table of Contents
+  * [List of Tables](#list-of-tables)
+  * [Revision](#revision)
+  * [About This Manual](#about-this-manual)
+  * [Scope](#scope)
+  * [Definition/Abbreviation](#definitionabbreviation)
+
+# List of Tables
+[Table 1: Abbreviations](#table-1-abbreviations)
+
+# Revision
+| Rev |     Date    |       Author       | Change Description                |
+|:---:|:-----------:|:------------------:|-----------------------------------|
+| 0.1 | 10/28/2019  | Nirenjan Krishnan  | Initial version                   |
+
+# About this Manual
+This document provides general information about the Docker to Host
+communication feature in SONiC.
+
+# Scope
+This document describes the high level design of Docker to Host communication.
+This describes the infrastructure provided by the feature, and example usage,
+however, it does not describe the individual host-specific features.
+
+# Definition/Abbreviation
+
+### Table 1: Abbreviations
+| **Term**                 | **Meaning**                         |
+|--------------------------|-------------------------------------|
+| XYZ                      | Term description                    |
+
+# 1 Feature Overview
+
+The management framework runs within a Docker container, and performs actions
+translating the user CLIs or REST requests to actions. Most of these actions
+perform some operation on the Redis database, but some of them require
+operations to be done on the host, i.e., outside the container. This document
+describes the host server, and translib API that are used to communicate between
+the Docker container and the host.
+
+
+## 1.1 Requirements
+
+### 1.1.1 Functional Requirements
+
+* The SONiC Management Framework and Telemetry containers must be able to issue
+  requests to the host, and return the responses from the host.
+* The individual applications that need access to the host must be able to
+  create a host module and easily issue requests and get responses back from the
+  host.
+* The host communication API shall be available in Translib, and shall provide
+  both synchronous and asynchronous communication methods.
+
+### 1.1.2 Configuration and Management Requirements
+
+N/A
+
+### 1.1.3 Scalability Requirements
+
+N/A
+
+### 1.1.4 Warm Boot Requirements
+
+N/A
+
+## 1.2 Design Overview
+### 1.2.1 Basic Approach
+
+The code will extend the existing Translib modules to provide a D-Bus based
+query API to issue requests to the host. The host service will be a Python based
+application which listens on known D-Bus endpoints.
+
+The individual app modules can extend the host service by providing a small
+Python snippet that will register against their application endpoint.
+
+### 1.2.2 Container
+
+SONiC Management Framework, gNMI Telemetry containers
+
+### 1.2.3 SAI Overview
+
+N/A
+
+# 2 Functionality
+## 2.1 Target Deployment Use Cases
+
+All deployments
+
+## 2.2 Functional Description
+
+This feature enables applications such as image management, ZTP, etc. to issue
+requests to the host to perform actions such as image install, ZTP
+enable/disable, etc.
+
+# 3 Design
+## 3.1 Overview
+
+The feature extends the SONiC management framework to add a D-Bus service on the
+host. This service will register against a known endpoint, and will service
+requests to the endpoint. Application modules will add snippets to the host
+service, which will automatically register their endpoints, and the app module
+in the container can use the APIs provided in Translib to send the request to
+the host, and either wait for the response (if the request was synchronous), or
+receive a channel and wait for the request to return the response on the
+channel (asynchronous request).
+
+## 3.2 DB Changes
+### 3.2.1 CONFIG DB
+N/A
+### 3.2.2 APP DB
+N/A
+### 3.2.3 STATE DB
+N/A
+### 3.2.4 ASIC DB
+N/A
+### 3.2.5 COUNTER DB
+N/A
+
+## 3.3 Switch State Service Design
+### 3.3.1 Orchestration Agent
+N/A
+### 3.3.2 Other Process
+N/A
+## 3.4 SyncD
+N/A
+## 3.5 SAI
+N/A
+
+## 3.6 User Interface
+### 3.6.1 Data Models
+N/A
+### 3.6.2 CLI
+#### 3.6.2.1 Configuration Commands
+N/A
+#### 3.6.2.2 Show Commands
+N/A
+#### 3.6.2.3 Debug Commands
+N/A
+#### 3.6.2.4 IS-CLI Compliance
+N/A
+### 3.6.3 REST API Support
+N/A
+
+# 4 Flow Diagrams
+
+![](images/docker-to-host-service.svg)
+
+# 5 Error Handling
+
+The `hostQuery` and `hostQueryAsync` APIs return a standard Go `error` object,
+which can be used to handle any errors that are returned by the D-Bus
+infrastructure.
+
+# 6 Serviceability and Debug
+N/A
+
+# 7 Warm Boot Support
+N/A
+
+# 8 Scalability
+N/A
+
+# 9 Unit Test
+List unit test cases added for this feature including warm boot.
+
+# 10 Internal Design Information
+N/A