Category Archives: Errors

AWS IoT – error in discovery certificate_verify_failed

Hi everyone,

I ran into the following error while using the AWS IoT python SDK:

Error in discovery!
Error message: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:720)

It turns out that this was because I was using the wrong root certificate. In the documentation there are five certificates listed:

  • RSA 2048 bit key: VeriSign Class 3 Public Primary G5 root CA certificate
  • RSA 2048 bit key: Amazon Root CA 1
  • RSA 4096 bit key: Amazon Root CA 2
  • ECC 256 bit key: Amazon Root CA 3
  • ECC 384 bit key: Amazon Root CA 4

If you’re using the console to create the certificate and have already downloaded your device cert, public cert and private key you can use Amazon Root CA 1:

As soon as that was added the error was resolved and I was able to move onto the next one. I found most of the info on the AWS forums but let me know if you have any questions:


Fetch As Google Error – ReactJs

Hi everyone,

I ran into the following error while using “fetch as Google” and none of my pages were being indexed correctly:

Uncaught TypeError: undefined is not a function

It took a while to find a solution but after some Googling I found that GoogleBot currently uses Chrome v41. You can download the mini installer of Chromium v41 which will run in parallel with your existing Chrome version:

After downloading Chromium you can just debug normally via the console. In my case, Chrome v41 didn’t like the following command:


If you’re using a front-end framework like ReactJS, AngularJS or Vue you’ll often just need to add babel polyfill:

npm install babel-core --save-dev

Then add this as the first line in your entry point e.g. index.js:

import 'babel-core/polyfill';

It’s important that the polyfill import is added as the first line otherwise anything added before it won’t work.

If you’re getting an error about Headers, you may also need to install the following:

import 'whatwg-fetch'

Add then add this import just below your babel polyfill:

npm install whatwg-fetch --save

Thanks to tomekrudzki on Reddit for the link to Chromium v41: Chrome 41 the key to successful website rendering



AWS 2_ContinuousDeliveryPipeline Tutorial – Error: no test specified

Hi everyone,

I ran into the following error while completing an AWS tutorial:

C:UsersChris-PCsourcereposUniApiuni-apitest>npm test

> uni-api-test@1.0.0 test C:UsersChris-PCsourcereposUniApiuni-api
> echo ‘Error: no test specified’

‘Error: no test specified’

The solution was to add the following line to my package.json file:

“scripts”: {“test”: “mocha”}

Now when running npm test I get the expected test output:

4 passing (24ms)
1 failing

1) Reading Unicorns
errors on missing unicorn data:

AssertionError [ERR_ASSERTION]: 500 == 404
+ expected – actual


at lambda.lambda_handler (testread.spec.js:77:20)
at appread.js:20:10
at Object.get (testread.spec.js:34:33)
at Object.exports.lambda_handler (appread.js:18:13)
at Context. (testread.spec.js:65:16)

npm ERR! Test failed. See above for more details.

Thanks to this link for the answer:

.NET Core 2.1 is Returning JSON with Lowercase Properties

Hi everyone,

Just testing out .Net Core 2.1 and noticed that all of my JSON properties are being returned in lowercase despite being defined as uppercase. It turns out that this is configurable:

// Change from this

// To this
        .AddJsonOptions(options => options.SerializerSettings.ContractResolver = new DefaultContractResolver());

Check out these links for more info:

AWS EC2 Elastic Beanstalk Going to Sleep – .Net/Windows/MSSQL Server Express

Hi everyone,

I’ve been having a bit of an issue with my AWS app going to sleep and taking a long time to handle initial requests.

I’m using .NET with Elastic Beanstalk on a T2 Micro Instance and MSSQL Server Express on RDS. My FrontEnd is a static ReactJS app that sits in S3 behind CloudFront. There’s also a load balancer across the backend.

My frontend was always instant but my initial Api calls were timing out. This ruled out S3 and CloudFront, leaving the following:

  • Load balancer
  • EC2/IIS

After a bit of Googling I came across something that looked fairly promising – MSSQL Server Express has a property called AutoClose set to ‘ON’ by default. AWS appears to correct this as mine was off however it’s worth checking:

-- If set to zero then auto close is off
SELECT DATABASEPROPERTY('mydatabasename','IsAutoShrink')

-- Check all instances at once
SELECT name,is_auto_close_on FROM sys.databases

-- Turn off if on

In my case the actual problem turned out to be IIS idle timeout. By default IIS automatically times out an application after 20 minutes. In order to disable this create the following ebextension:

        cwd: "C:\windows\system32\inetsrv"
        command: "appcmd set apppool / /.processModel.idleTimeout:0.00:00:00"

If you haven’t done this before, all you need to do is create a folder called .ebextensions under your project directory. Then create a new file called iis-idle-timeout.config and add the yaml to it. If you need more information on iis timing out check out this great blog post:

Thanks to these sources for the solutions:
Disable auto_close:
IIS Timeout:
EBExtension Info:

NavLink ListItems not Applying activeClassName class when Clicked On – ReactJS React-Router MaterialUI

Hi everyone,

A bit of a hairy issue I ran into today that took a while to track down. I’m using React Router with Material UI to render a Drawer as a sidebar:

The issue was that some links were not applying the expected activeclass:

	<ListItemText primary={
	} />

After trawling through react-router I eventually found a post on github that mentioned a similar issue:

The solution turned out to be wrapping all relevant components with withrouter.

Uncaught SyntaxError: Unexpected token < – ReactJS Build

Hi everyone,

A ReactJS issue I ran into after running npm run build:

Uncaught SyntaxError: Unexpected token <

This one took a while to track down but it essentially boils down to the built index.html file referencing paths relatively:

Issue: index.html was referencing

Instead of:

This meant that anytime a page was accessed directly it attempted to load the static files from the wrong directory. To fix it, I had to update the homepage node in package.json

"version": "0.1.0",
  "homepage": "./",
  "private": true,

Instead use:
"version": "0.1.0",
  "homepage": "/",
  "private": true,

Hopefully that’s able to help someone else out, took a while to track down!