Working with routes for WebSocket APIs - Amazon API Gateway

Working with routes for WebSocket APIs

In your WebSocket API, incoming JSON messages are directed to backend integrations based on routes that you configure. (Non-JSON messages are directed to a $default route that you configure.)

A route includes a route key, which is the value that is expected once a route selection expression is evaluated. The routeSelectionExpression is an attribute defined at the API level. It specifies a JSON property that is expected to be present in the message payload. For more information about route selection expressions, see Route selection expressions.

For example, if your JSON messages contain an action property and you want to perform different actions based on this property, your route selection expression might be ${request.body.action}. Your routing table would specify which action to perform by matching the value of the action property against the custom route key values that you have defined in the table.

There are three predefined routes that can be used: $connect, $disconnect, and $default. In addition, you can create custom routes.

  • API Gateway calls the $connect route when a persistent connection between the client and a WebSocket API is being initiated.

  • API Gateway calls the $disconnect route when the client or the server disconnects from the API.

  • API Gateway calls a custom route after the route selection expression is evaluated against the message if a matching route is found; the match determines which integration is invoked.

  • API Gateway calls the $default route if the route selection expression cannot be evaluated against the message or if no matching route is found.

Route selection expressions

A route selection expression is evaluated when the service is selecting the route to follow for an incoming message. The service uses the route whose routeKey exactly matches the evaluated value. If none match and a route with the $default route key exists, that route is selected. If no routes match the evaluated value and there is no $default route, the service returns an error. For WebSocket-based APIs, the expression should be of the form $request.body.{path_to_body_element}.

For example, suppose you are sending the following JSON message:

{ "service" : "chat", "action" : "join", "data" : { "room" : "room1234" } }

You might want to select your API's behavior based on the action property. In that case, you might define the following route selection expression:

$request.body.action

In this example, request.body refers to your message's JSON payload, and .action is a JSONPath expression. You can use any JSON path expression after request.body, but keep in mind that the result will be stringified. For example, if your JSONPath expression returns an array of two elements, that will be presented as the string "[item1, item2]". For this reason, it's a good practice to have your expression evaluate to a value and not an array or an object.

You can simply use a static value, or you can use multiple variables. The following table shows examples and their evaluated results against the preceding payload.

Expression Evaluated result Description
$request.body.action join An unwrapped variable
${request.body.action} join A wrapped variable
${request.body.service}/${request.body.action} chat/join Multiple variables with static values
${request.body.action}-${request.body.invalidPath} join If the JSONPath is not found, the variable is resolved as "".
action action Static value
\$default $default Static value

The evaluated result is used to find a route. If there is a route with a matching route key, the route is selected to process the message. If no matching route is found, then API Gateway tries to find the $default route if available. If the $default route is not defined, then API Gateway returns an error.

Set up routes for a WebSocket API in API Gateway

When you first create a new WebSocket API, there are three predefined routes: $connect, $disconnect, and $default. You can create them by using the console, API, or AWS CLI. If desired, you can create custom routes. For more information, see About WebSocket APIs in API Gateway.

Note

In the CLI, you can create routes before or after you create integrations, and you can reuse the same integration for multiple routes.

Create a route using the API Gateway console

To create a route using the API Gateway console

  1. Sign in to the API Gateway console, choose the API, and choose Routes.

  2. To create one of the predefined routes ($connect, $disconnect, and $default), choose its name.

  3. If desired, you can create custom routes. To do so, enter the route key name in the New Route Key text box and choose the checkmark icon.

    Note

    When you create a custom route, do not use the $ prefix in the route key name. This prefix is reserved for predefined routes.

Create a route using the AWS CLI

To create a route using the AWS CLI, call create-route as shown in the following example:

aws apigatewayv2 --region us-east-1 create-route --api-id aabbccddee --route-key $default

Example output:

{ "ApiKeyRequired": false, "AuthorizationType": "NONE", "RouteKey": "$default", "RouteId": "1122334" }

Specify route request settings for $connect

When you set up the $connect route for your API, the following optional settings are available to enable authorization for your API. For more information, see The $connect route.

  • Authorization: If no authorization is needed, you can specify NONE. Otherwise, you can specify:

    • AWS_IAM to use standard AWS IAM policies to control access to your API.

    • CUSTOM to implement authorization for an API by specifying a Lambda authorizer function that you have previously created. The authorizer can reside in your own AWS account or a different AWS account. For more information about Lambda authorizers, see Use API Gateway Lambda authorizers.

      Note

      In the API Gateway console, the CUSTOM setting is visible only after you have set up an authorizer function as described in Configure a Lambda authorizer using the API Gateway console.

    Important

    The Authorization setting is applied to the entire API, not just the $connect route. The $connect route protects the other routes, because it is called on every connection.

  • API Key Required: You can optionally require an API key for an API's $connect route. You can use API keys together with usage plans to control and track access to your APIs. For more information, see Creating and using usage plans with API keys.

Set up the $connect route request using the API Gateway console

To set up the $connect route request for a WebSocket API using the API Gateway console:

  1. Sign in to the API Gateway console, choose the API, and choose Routes.

  2. Under Routes, choose $connect.

  3. Choose Route Request in the route overview pane.

  4. Under Access Settings, configure the route settings as follows:

    1. To edit the Authorization setting, choose the pencil icon. Choose the desired setting from the dropdown menu and choose the checkmark icon to save the new setting.

    2. To edit the API Key Required setting, choose the pencil icon. Choose true or false from the dropdown menu and choose the checkmark icon to save the new setting.