Prevent lambda timeouts or failure from not handled promise due to invalid SSM parameter(s)... Add throwOnFailedCall flag to the SSM middleware

[bokjo]

What does this implement/fix? Explain your changes.

…
PR regarding #567

If you provide a non-existent SSM parameter to the @middy/ssm middleware it will cause the function to go to timeout if you are not using @middy/do-not-wait-for-empty-event-loop, or with do-not-wait-for-empty-event-loop in place, it will fail immediately (the error is thrown in the handleInvalidParams() function but it is not handled anywhere!) and not reach the original handler!

Changes:

• Added optional throwOnFailedCall flag with default value false (Same implementation as Secret Manager middleware)
• Added catch to the main Promise.all(ssmPromises)
  • If throwOnFailedCall=false it will just console.error the error and continue to the next middleware or main handler
  • If throwOnFailedCall=true it will console.error the error and throw the error thrown from handleInvalidParams()

p.s tested this implementation on AWS lambda with the code below... works as expected!

const middy = require('@middy/core')
const doNotWaitForEmptyEventLoop = require('@middy/do-not-wait-for-empty-event-loop')
const httpEventNormalizer = require('@middy/http-event-normalizer')
const httpSecurityHeaders = require('@middy/http-security-headers')
const ssm = require('@middy/ssm')

const hello = async (event, context) => {
  console.log('EVENT: ', event)
  console.log('CONTEXT: ', context)
  
  const { testSecret } = context
  console.log('testSecret: ', testSecret)

  return {
        statusCode: 200,
        body: JSON.stringify(context)
  }
}

module.exports.default = middy(hello)
  .use(doNotWaitForEmptyEventLoop({ runOnError: true }))
  .use(httpSecurityHeaders())
  .use(httpEventNormalizer())
  .use(
    ssm({
      cache: true,
      cacheExpiryInMillis: 60 * 1000, 
      names: {
        testSecret: process.env.SSM_PARAM
      },
      setToContext: true,
      throwOnFailedCall: false
    })
  )

Does this close any currently open issues?

No

Any relevant logs, error output, etc?

(If it’s long, please paste to https://ghostbin.com/ and insert the link here.)

Any other comments?

@willfarrell let me know if something else is needed! Don't have much time to check the documentation for do-not-wait-for-empty-event-loop

Some additional tests might be needed for the new throwOnFailedCall flag!

Where has this been tested?

Node.js Versions: : Node v12.18.3 (npm v6.14.6)

Middy Versions: : v1.4.0

AWS SDK Versions:: ^2.771.0

Todo list

• Feature/Fix fully implemented
• Added tests
• Add additional tests for throwOnFailedCall if needed
• Updated relevant documentation
• Updated relevant examples

[willfarrell]

Looks good. It will be part of v1.5.0. Just waiting on another PR related to ssm first.