Building a Real-time WebSocket Client - AWS AppSync

Building a Real-time WebSocket Client

AWS AppSync Real-time WebSocket client implementation guide for GraphQL Subscriptions

The following sequence diagram and steps show the real-time subscriptions workflow between the WebSocket client, HTTP client, and the AWS AppSync service.

  1. The client establishes a WebSocket connection with the AWS AppSync real-time endpoint. If there is a network error, the client should do a jittered exponential backoff. For more information, see Exponential Backoff And Jitter in the AWS Architecture Blog.

  2. After the WebSocket connection is successfully established, the client sends a connection_init message.

  3. The client waits for connection_ack message from AWS AppSync. This message includes a connectionTimeoutMs parameter, which is the maximum wait time in milliseconds for a "ka", keep-alive, message.

  4. AWS AppSync sends keep-alive messages, "ka", periodically. The client keeps track of the time it received each "ka" message. If no "ka" message is received within connectionTimeoutMs milliseconds, the client should terminate the connection.

  5. The client registers the subscription by sending a start subscription message. A single WebSocket connection supports multiple subscriptions even if they are in different authorization modes.

  6. The client waits for AWS AppSync to send start_ack messages to confirm successful subscriptions. If there is an error, AWS AppSync returns a "type": "error" message.

  7. The client listens for subscription events. Those are sent after a corresponding mutation was called. Queries and mutations are usually sent through https:// to the AWS AppSync GraphQL endpoint. Subscriptions flow through the AWS AppSync real-time endpoint using the secure WebSocket (wss://).

  8. The client unregisters the subscription by sending a stop subscription message.

  9. After unregistering all subscriptions and checking that there are no messages transferring through the WebSocket, the client can disconnect from the WebSocket connection.

Handshake details to establish the WebSocket connection

To connect and initiate a successful handshake with AWS AppSync, a WebSocket client needs the following:

  • The AppSync real-time endpoint

  • A query string that contains the following parameters: header and payload:

    • header: Contains information relevant to the AWS AppSync endpoint and authorization. This is a base64 string encoded from a stringified JSON object. The JSON object content varies depending on the authorization mode.

    • payload: Base64 encoded string of payload.

With these required details, a WebSocket client can connect to the URL, which is contains the API real-time endpoint with the query string, using graphql-ws as the WebSocket protocol.

Discovering the AWS AppSync real-time endpoint from the AWS AppSync GraphQL endpoint

The AWS AppSync GraphQL endpoint and the AWS AppSync real-time endpoint are slightly different in protocol and domain. You can retrieve the AWS AppSync GraphQL endpoint using the AWS CLI command aws appsync get-graphql-api.

AWS AppSync GraphQL endpoint:

https://example1234567890000.appsync-api.us-east-1.amazonaws.com/graphql

AWS AppSync real-time endpoint:

wss://example1234567890000.appsync-realtime-api.us-east-1.amazonaws.com/graphql

Applications can connect to the AWS AppSync GraphQL endpoint (https://) using any HTTP client for queries and mutations. Applications can connect to the AWS AppSync real-time endpoint (wss://) using any WebSocket client for subscriptions.

Header parameter format based on AWS AppSync API authorization mode

The format of the header object used in the connection query string varies depending to the AWS AppSync API authorization mode. The host field in the object refers to the AWS AppSync GraphQL endpoint, which is used to validate the connection even if the wss:// call is made against the real-time endpoint. To initiate the handshake and establish the authorized connection, the payload should be an empty JSON object.

API Key

Header contents:

  • "host": <string>: This is the host for the AWS AppSync GraphQL endpoint.

  • "x-api-key": <string>: API key configured for AWS AppSync API.

Example:

{ "host":"example1234567890000.appsync-api.us-east-1.amazonaws.com", "x-api-key":"da2-12345678901234567890123456" }

Payload content:

{}

Request URL:

wss://example1234567890000.appsync-realtime-api.us-east-1.amazonaws.com/graphql?header=eyJob3N0IjoiZXhhbXBsZTEyMzQ1Njc4OTAwMDAuYXBwc3luYy1hcGkudXMtZWFzdC0xLmFtYXpvbmF3cy5jb20iLCJ4LWFtei1kYXRlIjoiMjAyMDA0MDFUMDAxMDEwWiIsIngtYXBpLWtleSI6ImRhMi16NHc0NHZoczV6Z2MzZHRqNXNranJsbGxqaSJ9&payload=e30=

Amazon Cognito user pools and OpenID Connect (OIDC)

Header contents:

  • "Authorization": <string>: JWT Access Token.

  • "host": <string>: This is the host for the AWS AppSync GraphQL endpoint.

Example:

{ "Authorization":"eyEXAMPLEiJjbG5xb3A5eW5MK09QYXIrMTJHWEFLSXBieU5WNHhsQjEXAMPLEnM2WldvPSIsImFsZyI6IlEXAMPLEn0.eyEXAMPLEiJhNmNmMjcwNy0xNjgxLTQ1NDItOWYxOC1lNjY0MTg2NjlkMzYiLCJldmVudF9pZCI6ImVkMzM5MmNkLWNjYTMtNGM2OC1hNDYyLTJlZGI3ZTNmY2FjZiIsInRva2VuX3VzZSI6ImFjY2VzcyIsInNjb3BlIjoiYXdzLmNvZ25pdG8uc2lnbmluLnVzZXIuYWRtaW4iLCJhdXRoX3RpbWUiOjE1Njk0NTc3MTgsImlzcyI6Imh0dHBzOlwvXC9jb2duaXRvLWlkcC5hcC1zb3V0aGVhc3QtMi5hbWF6b25hd3MuY29tXC9hcC1zb3V0aGVhc3QtMl83OHY0SVZibVAiLCJleHAiOjE1Njk0NjEzMjAsImlhdCI6MTU2OTQ1NzcyMCwianRpIjoiNTgzZjhmYmMtMzk2MS00YzA4LWJhZTAtYzQyY2IxMTM5NDY5IiwiY2xpZW50X2lkIjoiM3FlajVlMXZmMzd1N3RoZWw0dG91dDJkMWwiLCJ1c2VybmFtZSI6ImVsb3EXAMPLEn0.B4EXAMPLEFNpJ6ikVp7e6DRee95V6Qi-zEE2DJH7sHOl2zxYi7f-SmEGoh2AD8emxQRYajByz-rE4Jh0QOymN2Ys-ZIkMpVBTPgu-TMWDyOHhDUmUj2OP82yeZ3wlZAtr_gM4LzjXUXmI_K2yGjuXfXTaa1mvQEBG0mQfVd7SfwXB-jcv4RYVi6j25qgow9Ew52ufurPqaK-3WAKG32KpV8J4-Wejq8t0c-yA7sb8EnB551b7TU93uKRiVVK3E55Nk5ADPoam_WYE45i3s5qVAP_-InW75NUoOCGTsS8YWMfb6ecHYJ-1j-bzA27zaT9VjctXn9byNFZmEXAMPLExw", "host":"example1234567890000.appsync-api.us-east-1.amazonaws.com" }

Payload content:

{}

Request URL:

wss://example1234567890000.appsync-realtime-api.us-east-1.amazonaws.com/graphql?header=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&payload=e30=

IAM

Header contents include the following:

  • "accept": "application/json, text/javascript": A constant <string> parameter.

  • "content-encoding": "amz-1.0": A constant <string> parameter.

  • "content-type": "application/json; charset=UTF-8": A constant <string> parameter.

  • "host": <string>: This is the host for the AWS AppSync GraphQL endpoint. - "x-amz-date": <string>: The timestamp must be in UTC and in the following ISO 8601 format: YYYYMMDD’T’HHMMSS’Z’. For example, 20150830T123600Z is a valid timestamp. Do not include milliseconds in the timestamp. For more information, see Handling dates in Signature Version 4 in the AWS General Reference.

The SigV4 signing HTTP request includes a canonical URL, which is the AWS AppSync GraphQL endpoint with /connect appended. The service endpoint AWS Region is same region where you’re using the AWS AppSync API, and service name is ‘appsync’. The HTTP request to sign is the following:

{ url: "https://example1234567890000.appsync-api.us-east-1.amazonaws.com/graphql/connect", data: "{}", method: "POST", headers: { "accept": "application/json, text/javascript", "content-encoding": "amz-1.0", "content-type": "application/json; charset=UTF-8", } }

Example:

{ "accept": "application/json, text/javascript", "content-encoding": "amz-1.0", "content-type": "application/json; charset=UTF-8", "host": "example1234567890000.appsync-api.us-east-1.amazonaws.com", "x-amz-date": "20200401T001010Z", "X-Amz-Security-Token": "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", "Authorization": "AWS4-HMAC-SHA256 Credential=XXXXXXXXXXXXXXXXXXX/20200401/us-east-1/appsync/aws4_request, SignedHeaders=accept;content-encoding;content-type;host;x-amz-date;x-amz-security-token, Signature=83EXAMPLEbcc1fe3ee69f75cd5ebbf4cb4f150e4f99cec869f149c5EXAMPLEdc" }

Payload content:

{}

Request URL:

wss://example1234567890000.appsync-realtime-api.us-east-1.amazonaws.com/graphql?header=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&payload=e30=

Note: One WebSocket connection can have multiple subscriptions (even with different authentication modes). One way to implement this is to create a WebSocket connection for the first subscription and close it when the last subscription is unregistered. This could be optimized by waiting a few seconds before closing the WebSocket connection, in case the App is subscribed immediately after the last subscription is unregistered. For a mobile app example, when changing from one screen to another, on unmounting event, it stops a subscription and on mounting event, it starts a different subscription.

Real-time WebSocket Operation

After initiating a successful WebSocket handshake with AWS AppSync, the client needs to send a subsequent message to complete the connection step to AWS AppSync for different operations. These messages require the following data:

  • type: The type of the operation.

  • id: An unique identifier for the subscription. We recommend using a UUID for this purpose.

  • payload: Associated payload depending of the operation type.

The type field is the only required field, with id and payload optional.

Sequence of events

To successfully initiate, establish, register and process the subscription request, the client must step through the following sequence:

  1. Initialize connection (connection_init)

  2. Connection acknowledgment (connection_ack)

  3. Subscription registration (start)

  4. Subscription acknowledgment (start_ack)

  5. Processing subscription (data)

  6. Subscription unregistration (stop)

Connection init message

After a successful handshake, the client must send the connection_init message to start the communication with the AWS AppSync real-time endpoint. Without this step, all other messages will be ignored. The message is a string obtained by stringifying the following JSON object as follows:

{ "type": "connection_init" }

Connection acknowledge message

After sending the connection_init message, the client must wait for the connection_ack message. All messages sent before receiving connection_ack will be ignored. The message should read as follows:

{ "type": "connection_ack", "payload": { // Time in milliseconds waiting for ka message before the client should terminate the WebSocket connection "connectionTimeout": 300000 } }

Keep-alive message

In addition to the connection acknowledge message, the client periodically receives keep-alive messages. If no keep-alive message is received within the connection timeout period, the client should terminate the connection. AWS AppSync will keep sending these messages and servicing the registered subscriptions until it shuts down the connection automatically (after 24 hours). Keep-alive messages are heartbeats and do not need to be acknowledged by the client.

{ "type": "ka" }

Subscription registration message

After connection_ack message is received by the client, subscription registration messages can be sent to AWS AppSync. This message is a stringified JSON object that contains the following fields:

  • "id": <string>: ID of the subscription. This id must be unique for each subscription, otherwise the server will return an error indicating that the subscription id is duplicated.

  • "type": "start": A constant <string> parameter.

  • "payload": <Object>: This contains the information relevant to the subscription.

    • "data": <string>: Stringified JSON object that contains GraphQL query and variables.

      • "query": <string>: GraphQL operation.

      • "variables": <Object>: Contains the variables for the query.

    • "extensions": <Object>: This contains authorization object.

  • "authorization": <Object>: This contains the fields required for authorization.

Authorization object for subscription registration

The same rules in the Header parameter format based on AWS AppSync API authorization mode section apply for the authorization object. The only exception is for IAM, where the SigV4 signature information is slightly different. For more details, see the IAM example.

Example using Amazon Cognito user pools:

{ "id": "ee849ef0-cf23-4cb8-9fcb-152ae4fd1e69", "payload": { "data": "{\"query\":\"subscription onCreateMessage {\\n onCreateMessage {\\n __typename\\n message\\n }\\n }\",\"variables\":{}}", "extensions": { "authorization": { "Authorization": "eyEXAMPLEiJjbG5xb3A5eW5MK09QYXIrMTJEXAMPLEBieU5WNHhsQjhPVW9YMnM2WldvPSIsImFsZyI6IlEXAMPLEn0.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.CT-qTCtrYeboUJ4luRSTPXaNewNeEXAMPLE14C6sfg05tO0fOMpiUwj9k19gtNCCMqoSsjtQoUweFnH4JYa5EXAMPLEVxOyQEQ4G7jQrt5Ks6STn53vuseR3zRW9snWgwz7t3ZmQU-RWvW7yQU3sNQRLEXAMPLEcd0yufBiCYs3dfQxTTdvR1B6Wz6CD78lfNeKqfzzUn2beMoup2h6EXAMPLE4ow8cUPUPvG0DzRtHNMbWskjPanu7OuoZ8iFO_Eot9kTtAlVKYoNbWkZhkD8dxutyoU4RSH5JoLAnrGF5c8iKgv0B2dfEXAMPLEIihxaZVJ9w9w48S4EXAMPLEcA", "host": "example1234567890000.appsync-api.us-east-1.amazonaws.com" } } }, "type": "start" }

Example using IAM:

{ "id": "eEXAMPLE-cf23-1234-5678-152EXAMPLE69", "payload": { "data": "{\"query\":\"subscription onCreateMessage {\\n onCreateMessage {\\n __typename\\n message\\n }\\n }\",\"variables\":{}}", "extensions": { "authorization": { "accept": "application/json, text/javascript", "content-type": "application/json; charset=UTF-8", "X-Amz-Security-Token": "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", "Authorization": "AWS4-HMAC-SHA256 Credential=XXXXXXXXXXXXXXXXXXXX/20200401/us-east-1/appsync/aws4_request, SignedHeaders=accept;content-encoding;content-type;host;x-amz-date;x-amz-security-token, Signature=b90131a61a7c4318e1c35ead5dbfdeb46339a7585bbdbeceeaff51f4022eb1fd", "content-encoding": "amz-1.0", "host": "example1234567890000.appsync-api.us-east-1.amazonaws.com", "x-amz-date": "20200401T001010Z" } } }, "type": "start" }

The SigV4 signature does not need /connect to be appended to the url and data is replaced with the JSON stringified GraphQL operation. Following is an example of a SigV4 signature request:

{ url: "https://example1234567890000.appsync-api.us-east-1.amazonaws.com/graphql", data: "{\"query\":\"subscription onCreateMessage {\\n onCreateMessage {\\n __typename\\n message\\n }\\n }\",\"variables\":{}}", method: "POST", headers: { "accept": "application/json, text/javascript", "content-encoding": "amz-1.0", "content-type": "application/json; charset=UTF-8", } }

Subscription acknowledge message

After sending the subscription start message, the client should wait for AWS AppSync to send the start_ack message. start_ack indicates the subscription was successful. The message is the following string:

Subscription success example:

{ "type": "start_ack", "id": "eEXAMPLE-cf23-1234-5678-152EXAMPLE69" }

Error message

If connection init or subscription registration fails or if a subscription is terminated from the server, the server sends the following error message to the client:

  • "type": "error": A constant <string> parameter.

  • "id": <string>: The id of the corresponding registered subscription, if relevant.

  • "payload" <Object>: This object contains the corresponding error information.

Example:

{ "type": "error", "payload": { "errors": [ { "errorType": "LimitExceededError", "message": "Rate limit exceeded" } ] } }

Processing data messages

When a client submits a mutation, AWS AppSync identifies all of the subscribers interested in it and sends a "type":"data" message to each, using the corresponding subscription id used in the "start" subscription operation. The client is expected to keep track of the subscription id it sends so that when a data message is received, the client can match it with the corresponding subscription.

  • "type": "data": A constant <string> parameter.

  • "id": <string>: The id of the corresponding registered subscription.

  • "payload" <Object>: This object contains data object with the subscription information.

Example:

{ "type": "data", "id": "ee849ef0-cf23-4cb8-9fcb-152ae4fd1e69", "payload": { "data": { "onCreateMessage": { "__typename": "Message", "message": "test" } } } }

Subscription unregistration message

When the App wants to stop listening to the subscription events, the client should send a message with the following stringified JSON object:

  • "type": "stop": A constant <string> parameter.

  • "id": <string>: The id of the subscription that will be unregistered.

Example:

{ "type":"stop", "id":"ee849ef0-cf23-4cb8-9fcb-152ae4fd1e69" }

AWS AppSync sends back a confirmation message with the following stringified JSON object:

  • "type": "complete": A constant <string> parameter.

  • "id": <string>: The id of the unregistered subscription.

No more messages will be sent for this particular subscription after the message is received.

Example:

{ "type":"complete", "id":"eEXAMPLE-cf23-1234-5678-152EXAMPLE69" }

Disconnecting the WebSocket

Before disconnecting, the client should have the necessary logic to check that no operation is currently in place through the WebSocket connection to avoid data loss. All subscriptions should be unregistered before disconnecting from the WebSocket.