Category Archives: How To

Scan a Redis Cluster

The Redis SCAN command allows you to iterate over the key space. On a single Redis node you can SCAN all keys or just keys matching a pattern. It’s a slow operation: O(N) where N is the number of keys in the database. However, it can be useful when you want to view every item in the database or when there’s no way to find your values without traversing everything. Due to the way that Redis shards data though, it may be difficult to SCAN keys on a Redis Cluster. It is possible but it takes a little more work.

Testing Spring reactive WebClient

The reactive WebClient does not yet have the mature test support that RestTemplate now has. There is not yet a standard recipe to test Spring WebClient applications. No doubt support will be improved in future versions but for now, here’s what works for me.

Securing a Zookeeper ensemble

Even in secured networks, it’s a good idea to use some of the security features available in Zookeeper. In this post we’ll look at two security mechanisms: mutual TLS (mTLS) and SASL authentication. We’ll set up these security features on the server-server communication (leader election protocols) and client-server communication (Kafta to Zookeeper).

Building a Zookeeper ensemble

Some notes on setting up and configuring a Zookeeper ensemble. Many guides use some shortcuts to setting up the ensemble such as running multiple Zookeeper instances on a single machine or running them in Docker. Both require some workarounds to make it work. As a better example, this guide runs three Zookeeper instances across three different VMs.

Microsoft Bot Framework Part 3: Connect to channels

In the first two parts we built a bot using the Microsoft Bot Framework SDK and registered it in Azure. In this third and final part we’ll consume the bot using three of the available Bot Framework Channels: A simple chat component on a web page, SMS text and a fully custom Node.js application.

Microsoft Bot Framework Part 2: Build a bot with Bot Framework SDK

In the first part, we created an Azure Bot registration and connected to a demo bot application. In this part we’ll swap out the demo bot for one we’ve built using the Microsoft Bot Framework SDK.

Microsoft Bot Framework Part 1: Create an Azure Bot Resource

In this part, I’ll register and configure a bot with Microsoft Azure Bot Service. It might seem odd to start here rather than going straight into the application code. However, getting this step out of the way gives us something simple to play with that works end to end.

Execute Around idiom in Java

The Execute Around idiom is a pattern that allows you to wrap an action with some standard setup / tear down steps. Examples might include: Execute within a lock: acquire the lock, do the action, release the lock Resource handling: acquire the resource, do the action, close the resource Execute as a user: switch to read more »

Reverse order a Stream in Java

How do you reverse order a Stream in Java? There’s no obvious Stream.reverse() method. Is this an oversight in the API? Is there a workaround?

Initialize a Windows container with an entrypoint script

A popular Docker article describes a pattern to initialize stateful container data at runtime. The example uses a Shell script to run the initialization and then pass control to the container’s main command. We can use the same pattern to initialize a Docker Windows container.