Don't Panic!

Spring Cloud Data Flow on Kubernetes

Published on February 29, 2020

Spring Cloud Data Flow is a powerful tool for composing and deploying message driven data pipelines. It allows us to compose simple Spring Cloud Stream applications into complex processing pipelines. It also takes care of deploying these pipelines into Kubernetes or into Cloud Foundry.

It’s powerful but has a lot of moving parts. It can be daunting to get a simple pipeline running. This article introduces the Primer demo for SCDF and describes how to deploy it into Kubernetes on a local development machine.

Secrets in Google App Engine

Published on April 27, 2019

Google App Engine makes it easy to deploy NodeJS applications. The GAE Standard Environment and SDK support NodeJS out of the box. This makes Google App Engine a great choice ahead of competitors such as Heroku, AWS or Microsoft Azure. Unfortunately though, there’s no support for managing secrets in Google App Engine. When I deployed Dog n Bone to GAE, I found this single shortcoming the main source of complexity.

There are however some workarounds. None of them is particularly nice though.

Detecting Twilio API login failures

Published on February 24, 2019

When I built out Dog n Bone – a browser phone powered by Twilio, I found that behavior on providing an incorrect accountSid / authToken was not quite what I expected. This post details how I detected Twilio API login failures in Dog n Bone.

Twilio uses ClientCapability tokens to grant access to API features. The back end obtains a ClientCapability object using a Twilio accountSid and authToken. It sets scopes on the ClientCapability to grant only necessary permissions on that account. API requests in the front end authenticate using the JWT created from the CapabilityToken. This mechanism allows the front end to authenticate to the API without exposing the Twilio accountSid / authToken.

SSH into a Docker Container

Published on November 30, 2018

Just sometimes, it’s useful to SSH into a Docker Container. While docker exec or docker attach are usually sufficient to run commands in a container, sometimes you specifically need SSH. For example, to connect directly from a remote machine or when an application needs to run commands on your container. Most Docker images don’t come with the SSHd service installed so it is not possible to SSH to them. This post demonstrates how to install and run the SSHd service to an existing image so that you can connect to it.

Unit test time based logic

Published on October 23, 2018

A standard unit testing problem is how to unit test code that has a dependency on dates or times. For example a method that returns a greeting according to the time of day:

public String timeOfDayGreeting() {
    LocalTime now = LocalTime.now();
    if (now.isBefore(LocalTime.NOON)) {
        return "Good morning";
    } else if (now.isBefore(LocalTime.of(18, 00))) {
        return "Good afternoon";
    } else {
        return "Good evening";
    }
}

If we were to call this method from a test fixture (say JUnit), it would return different values depending on when the test was run. This is not ideal. Unit tests should pass or fail consistently.

Here’s a simple solution for testing time based code.

Test First React part 2: API calls and Mocks

Published on September 23, 2018

This article demonstrates some more advanced test first React practices. Specifically, API calls and mocks.

Test First React part 1: setup and first tests

Published on August 25, 2018

React is a great choice for writing test first client side Javascript. The test ecosystem is mature enough to enable test first development of complex components. This article shows how to build a React component test first and introduces supporting test libraries Jest and Enzyme. In the next article we’ll look at more advanced testing including API testing and module mocking.

Test log4j2 with JUnit using a custom appender

Published on April 29, 2018

In previous articles, I’ve described how to test System.out with JUnit and how to test log4j with JUnit. This article describes how to test log4j2…

Test log4j with JUnit using a custom appender

Published on January 15, 2018

Following a recent article on how to Test System.out with JUnit, here’s a follow up on how to test log4J with JUnit. This article describes a technique to test log4J output in a JUnit test by adding a custom appender. This allows us to verify that log4j output contains expected Strings.

Validate JSPs at build time

Published on November 13, 2017

JSPs compile to Java code at run time. This is helpful if we want to test code changes without a build and deploy. However, if errors are introduced, they may not be spotted till it’s too late. A useful compromise is to validate JSPs at build time to verify that they will compile. The validator catches syntax errors before the application deploys and starts. This speeds up our build and test cycle and prevents silly mistakes slipping through to production code.

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