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Exploration of Tanzu Kubernetes Grid (TKG) multi-vCenter Server templating using YTT

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The motivation behind this blog post originates from a really cool blog post by Mike Brown who shared an interesting Telco use case for wanting to running Tanzu Kubernetes Grid (TKG) on VMware Cloud on AWS (VMConAWS) and centrally managing TKG Workload Clusters, which would run at each individual Edge/Cell Site location.

While reading through Mike's blog post, I noticed one of the steps was to edit the generated YAML from the TKG Management Cluster which would then be used to deploy the individual TKG Workload Clusters. This would need to happen for each new deployment 😮 and of course, this could be very error prone and frustrating for end users. Here is an example of what the YAML file looks like which is over 1K+ lines!

This screams for automation and I had been looking for a reason to try out YTT again, which is a YAML templating tool that is part of the open source project Carvel. Although I had played with YTT before, it did not feel intuitive, especially for a new user who was trying to solve a quick problem. I figured this was my opportunity to take another look at YTT.

After a couple of hours and a lot of trial/error, I ended up with a partial solution and realized that I would not be able to figure this out given there were even more complicated sections within the YAML. I felt the bar to getting started with YTT was still too high and it may not be the right tool for this particular situation. I opted for a quicker solution using sed, which I had experience with before, but I also know that depending on the problem, sed can be just as complex and I also dislike regular expressions  🙂

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Customizing Kubernetes cluster template (Dev/Prod) plans in Tanzu Kubernetes Grid 1.2

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With previous releases of Tanzu Kubernetes Grid (TKG), if you needed to apply special OS customizations that were applied to the deployed Control Plane and Worker Node VMs, such as injecting commands to handle network proxy or dealing with insecure container registry, your only option was to hand edit the default TKG Dev/Prod YAML templates. Not only was this error prone but because the templates can change from each release, it was difficult to manage and test until you attempted a deployment.

One of the newest features with the release of TKG 1.2 is official support for customizing the Kubernetes (K8s) Cluster Templates Plans using YTT (YAML Templating Tooling) which allows users to provide custom data that can then be patched/overlay to an existing YAML file. YTT itself is part of a larger toolset for building, creating and configuring deployments for K8s called Carvel. The Domain Specific Language (DSL) that YTT uses was not exactly intuitive but since the official TKG documentation had an example to start with, I was able to mostly figure my way through along with some tips from the #carvel Slack channel.

So what was I trying to do? I was working on updating my TKG Demo Appliance Fling to the latest 1.2 release and part of the setup required adding an entry to /etc/hosts file on all TKG VMs that are deployed. Instead of directly messing with the YAML templates, there is now a new "overlay" YAML file in ~/.tkg/providers/infrastructure-vsphere/ytt/vsphere-overlay.yaml which can be used to make such changes.

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