Use Postman to test Appsync Subscription

Since Postman supports WebSockets testing GraphQL subscriptions is achievable as well. Such a testing requires two steps:

• connection to a server,
• sending a start message.

Establishing a connection:

1. Create a new WebSocket request.
2. Put your server URL ws:// or wss://.
3. Add custom header parameter Sec-WebSocket-Protocol: graphql-ws. Other headers may depend on your server configuration.
4. Press the "Connect" button.

When the connection is established we may start a subscription.

1. In the "New message" field put the command.
2. Press the "Send" button.

The start message should look like this:

{
  "id":"1",
  "payload": {
      "operationName": "MySubscription",
      "query": "subscription MySubscription {
          someSubscription {
              __typename
              someField1
              someField2 {
                  __typename
                  someField21
                  someField22
              }
          }
      }",
      "variables": null
  },
  "type": "start"
}

operationName is just the name of your subscription, I guess it's optional. And someSubscription must be a subscription type from your schema.

query reminds regular GraphQL syntax with one difference:

• __typename keyword precedes every field list.

For example, the query from the payload in regular syntax looks like the following:

subscription MySubscription {
  someSubscription {
        someField1
        someField2 {
              someField21
              someField22
        }
  }
}

Example message with parameters (variables):

{
      "id":"1",
      "payload": {
           "operationName": "MySubscription",
           "query": "subscription MySubscription($param1: String!) {
                  someSubscription((param1: $param1)) {
                      __typename
                      someField
                  }
            }",
            "variables": {
                  "param1": "MyValue"
            }
      },
      "type": "start"
}

It also reminds regular GraphQL syntax as described above.

variables is an object with your parameters.