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serverlessaws-appsyncaws-serverless

Serverless - Change the content before deploy

I'm using Serverless for working with our aws lambda / appsync. For Error Handling, we are keep erro code with message in a json file. The Codes will be unique. Something like this:

//error-code.json
{ 
 "1"": { code: 1, message: "Invalid User Input"},
 "2"": { code: 2, message: "Invalid Input"},
  //... so on
}

This wil lbe deploy as layer and all the lambda will use it. Issue is we cannot use it in the resolve template. There are some of the resolver will be only template file. These template files cannot access the json file nor can access the layer. How can I use the error-code.json here?

Solution 1:
Manually write the error code in templates and make sure there are alway unique. Something like this:

#set(#errorInfo = {
 "erroCode": "1",
 "errorMessage": "Invalid Input"
})
$util.error("Invalid Input", "errorType", $ctx.arguments,#errorInfo)

Rejected: Becasue we have to manually check everytime for the unique of error code. In case of lot of template file, we cannot rely on it.

Solution 2:
Create a table with error code (unique) and error message. Use this table to send error from template. Rejected: Because we use multiple app sync instance and they all connect to dirferent database. So we have to make this table in all database, and thus unique across the app-sync is not maintained.

Solution 3:
Write the placeholder in vtl where we want to send the error. Before Deploy, replace the placeholder with the actual code using pre-hook script, but not in the actual vtl file but in the generated package that serverless deploy. Does Serverless even such thing?

Solution

  • if your errors are all static, there is one more option for consideration. You create one more file that holds all errors defined in Velocity.

    $util.qr( $ctx.stash.put("errors", {}) ) $util.qr(

    $util.qr( $ctx.stash.errors.put("ONE", { "code": 1, "message": "Invalid User Input"} )

    ...

    $util.qr( $ctx.stash.errors.put("TWENTY", { "code": 20, "message": "20th error description"} )

    For every velocity resolver that throws errors, you inject pre-defined errors at the beginning of its request mapping's file. Whenever you want to throw an error, it's done by retrieving a pre-defined error from $ctx.stash

    $util.error ( $ctx.stash.errors.ONE.message, $ctx.stash.errors.ONE.code )

    The error file is generated from error-code.json, or manually typed again for simplicity. $ctx.stash is used because stash is accessible from everywhere in a resolver, including pipeline ones.