diff --git a/specification/containerinstance/resource-manager/Microsoft.ContainerInstance/preview/2018-02-01-preview/containerInstance.json b/specification/containerinstance/resource-manager/Microsoft.ContainerInstance/preview/2018-02-01-preview/containerInstance.json
index 1255caeaab4c..673543793ad0 100644
--- a/specification/containerinstance/resource-manager/Microsoft.ContainerInstance/preview/2018-02-01-preview/containerInstance.json
+++ b/specification/containerinstance/resource-manager/Microsoft.ContainerInstance/preview/2018-02-01-preview/containerInstance.json
@@ -179,7 +179,8 @@
               "$ref": "#/definitions/ContainerGroup"
             }
           }
-        }
+        }, 
+        "x-ms-long-running-operation": true
       },
       "patch": {
         "operationId": "ContainerGroups_Update",
@@ -206,6 +207,7 @@
           {
             "name": "Resource",
             "description": "The container group resource with just the tags to be updated.",
+            "required": true,
             "in": "body",
             "schema": {
               "$ref": "#/definitions/Resource"
@@ -360,6 +362,56 @@
           }
         }
       }
+    },
+    "/subscriptions/{subscriptionId}/resourceGroups/{resourceGroupName}/providers/Microsoft.ContainerInstance/containerGroups/{containerGroupName}/containers/{containerName}/exec": {
+      "post": {
+        "operationId": "StartContainer_LaunchExec",
+        "x-ms-examples": {
+          "ContainerExecStart": {
+            "$ref": "./examples/ContainerExecStart.json"
+          }
+        },
+        "summary": "Starts the exec command for a specific container instance.",
+        "description": "Starts the exec command for a specified container instance in a specified resource group and container group.",
+        "parameters": [
+          {
+            "$ref": "#/parameters/SubscriptionIdParameter"
+          },
+          {
+            "$ref": "#/parameters/ApiVersionParameter"
+          },
+          {
+            "$ref": "#/parameters/ResourceGroupNameParameter"
+          },
+          {
+            "$ref": "#/parameters/ContainerGroupNameParameter"
+          },
+          {
+            "name": "containerName",
+            "in": "path",
+            "description": "The name of the container instance.",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name":"containerExecRequest",
+            "in":"body",
+            "description":"The request for the exec command.",
+            "required":true,
+            "schema":{
+                "$ref":"#/definitions/ContainerExecRequest"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "OK",
+            "schema": {
+              "$ref": "#/definitions/ContainerExecResponse"
+            }
+          }
+        }
+      }
     }
   },
   "definitions": {
@@ -1057,6 +1109,44 @@
         }
       }
     },
+    "ContainerExecRequest": {
+      "description": "The start container exec request.",
+      "type": "object",
+      "properties": {
+        "command": {
+          "type": "string",
+          "description": "The command to be executed."
+        },
+        "terminalSize": {
+          "type": "object",
+          "description": "The size of the terminal.",
+          "properties": {
+            "row":{
+              "type": "integer",
+              "description": "The row size of the terminal"
+            },
+            "column": {
+              "type": "integer",
+              "description": "The column size of the terminal"
+            }
+          }
+        }
+      }
+    },
+    "ContainerExecResponse": {
+      "description": "The information for the container exec command.",
+      "type": "object",
+      "properties": {
+        "webSocketUri": {
+          "type": "string",
+          "description": "The uri for the exec websocket."
+        },
+        "password": {
+          "type": "string",
+          "description": "The password to start the exec command."
+        }
+      }
+    },
     "Resource": {
       "type": "object",
       "description": "The Resource model definition.",
@@ -1131,6 +1221,14 @@
       "type": "string",
       "description": "The name of the container group.",
       "x-ms-parameter-location": "method"
+    },
+    "OperationIdParameter": {
+      "name": "operationId",
+      "in": "path",
+      "required": true,
+      "type": "string",
+      "description": "The operation Id.",
+      "x-ms-parameter-location": "method"
     }
   }
 }
diff --git a/specification/containerinstance/resource-manager/Microsoft.ContainerInstance/preview/2018-02-01-preview/examples/ContainerExecStart.json b/specification/containerinstance/resource-manager/Microsoft.ContainerInstance/preview/2018-02-01-preview/examples/ContainerExecStart.json
new file mode 100644
index 000000000000..f1136352bed8
--- /dev/null
+++ b/specification/containerinstance/resource-manager/Microsoft.ContainerInstance/preview/2018-02-01-preview/examples/ContainerExecStart.json
@@ -0,0 +1,24 @@
+{
+    "parameters": {
+      "subscriptionId": "subid",
+      "api-version": "2018-02-01-preview",
+      "resourceGroupName": "demo",
+      "containerGroupName": "demo1",
+      "containerName": "container1",
+      "containerExecRequest": {
+          "command": "/bin/bash",
+          "terminalSize": {
+              "row": 12,
+              "column": 12
+          }
+      }
+    },
+    "responses": {
+      "200": {
+        "body": {
+          "webSocketUri": "wss://web-socket-uri",
+          "password": "password"
+        }
+      }
+    }
+  }
\ No newline at end of file
diff --git a/specification/containerinstance/resource-manager/Microsoft.ContainerInstance/preview/2018-02-01-preview/examples/ContainerGroupAsyncOperation.json b/specification/containerinstance/resource-manager/Microsoft.ContainerInstance/preview/2018-02-01-preview/examples/ContainerGroupAsyncOperation.json
new file mode 100644
index 000000000000..29475e5348c5
--- /dev/null
+++ b/specification/containerinstance/resource-manager/Microsoft.ContainerInstance/preview/2018-02-01-preview/examples/ContainerGroupAsyncOperation.json
@@ -0,0 +1,17 @@
+{
+    "parameters": {
+      "subscriptionId": "subid",
+      "location": "westcentralus",
+      "operationId": "operationId",
+      "api-version": "2018-02-01-preview"
+    },
+    "responses": {
+      "200": {
+        "body": {
+          "id": "/subscriptions/subid/resourceGroups/demo/providers/Microsoft.ContainerInstance/containerGroups/demo1",
+          "status": "Creating"
+        }
+      }
+    }
+  }
+  
\ No newline at end of file
diff --git a/specification/containerinstance/resource-manager/readme.md b/specification/containerinstance/resource-manager/readme.md
index 9709cab633a3..06ac2b7cf2fe 100644
--- a/specification/containerinstance/resource-manager/readme.md
+++ b/specification/containerinstance/resource-manager/readme.md
@@ -115,7 +115,7 @@ python:
   payload-flattening-threshold: 2
   namespace: azure.mgmt.containerinstance
   package-name: azure-mgmt-containerinstance
-  package-version: 0.2.0
+  package-version: 0.4.0
   clear-output-folder: true
 ```
 ``` yaml $(python) && $(python-mode) == 'update'