iidy fails silently if AWS metadata service 404s

[cschmidt]

If you happen to be running iidy in an environment where the credentials are not found, iidy will fail silently. In particular, I noticed this running iidy under AWS Cloud9. Running iidy render on a template would produce no output.

Manually configuring AWS credentials with aws configure works around the issue.

[cschmidt]

@tavisrudd noted that the tell-tale sign you were running into this issue was that you'd get a 404 from the AWS metadata service (http://169.254.169.254/latest/meta-data/iam/)

[cschmidt]

Just some further thinking on this. I'm not sure if the lack of iam meta-data is actually a bug in the Cloud9 environment. Reading through the docs on AWS Managed Temporary Credentials it seems like this might be a feature.

[tavisrudd]

If not a bug in Cloud9, it's a bug in the aws-sdk for js. That's what handles the lookup via the metadata service. Regardless, we can improve iidy's error reporting for this case.

[tavisrudd]

cschmidt:~/environment (master) $ iidy --debug render cfn-template.yaml 
error:  Error: null
    at IncomingMessage.<anonymous> (/snapshot/cf_templates/node_modules/aws-sdk/lib/util.js:864:34)
    at emitNone (events.js:110:20)
    at IncomingMessage.emit (events.js:207:7)
    at endReadableNT (_stream_readable.js:1045:12)
    at _combinedTickCallback (internal/process/next_tick.js:102:11)
    at process._tickDomainCallback (internal/process/next_tick.js:198:9)

is the stack trace Carl encountered.

[tavisrudd]

A related issue is that if you run iidy from a location that has neither ~/.aws/ or the AWS metadata service it will either error immediately with error connect ECONNREFUSED 169.254.169.254:80 or it will hang for a while before exiting with error: connect ETIMEDOUT 169.254.169.254:80.

[tavisrudd]

PR #120 addresses ETIMEDOUT and ECONNREFUSED but not the original 404 that @cschmidt encountered.