Elan Thomas England

Welcome to my site! This is a simple portfolio site which discusses some projects that I’ve built.

Scroll down to read an introduction to each project, and click the heading to see the full write-up.

Shellbin

Shellbin is a microservice architecture project that I built to exercise my understanding of CI/CD for cloud-native applications.

It’s named shellbin because it’s a pastebin clone that you can access with your shell using Unix pipes and the netcat utility.

cat $FILE | nc <address> <port>

Users can also create pastes using a web front-end written in Go that uses server-side rendering.

  flowchart LR
    Browser[Browser / HTTP client]
    Netcat[Netcat / TCP client]

    subgraph K8s["Kubernetes"]
      WS[webserver<br/>Gin on :4747<br/>Service port 80]
      NC[nc-server<br/>TCP on :6262<br/>Service targetPort 6262]
      DB[db-service<br/>Gin on :7272<br/>Service port 80]
      MYSQL[(MySQL)]
    end
    class K8s k8slabel
    classDef k8slabel color:#ffffff 

    Browser -->|GET /, GET /paste/:path, POST /submit| WS
    Netcat -->|TCP paste content| NC

    WS -->|HTTP POST /processInput| DB
    WS -->|HTTP POST /servePaste| DB
    NC -->|HTTP POST /processInput| DB

    DB -->|SQL queries to pastes table| MYSQL

In total, there are 4 discrete container images involved in this project: A web server, a database service, a netcat-receiving-server, and the MySQL database container.

As mentioned, the main goal of this project was to experiment with a development pipeline for these microservices.

The CI/CD pipeline ends up being pretty simple:

• First, shellbin’s Kubernetes manifests are sourced from a Helm chart that is tracked by ArgoCD
  • ArgoCD makes sure that the most recent versions of the application manifests are deployed
• When we push to the shellbin repo, our GitHub Actions workflow goes something like this:
  • builds the container images, then pushes them to GitHub Container Registry (GHCR)
  • clones the Kubernetes cluster’s declarative GitOps repository
  • modifies the image tags in the Helm Chart’s values.yml so they point to the newly pushed images
  • commits and pushes the diff that has the new image tags to cluster’s configuration repo
• And then ArgoCD picks up changes and the cluster deploys updates to the container images and Helm Chart

Read the full Shellbin write-up here for more details.

Webterm

Webterm is a system that allows users to access Unix machines from their web browser.

Here are some of the moving-pieces involved with this project:

• Website frontend that visually emulates a terminal in the browser
• Client-side JavaScript that requests a terminal assignment from the backend
• Client-side JavaScript that connects the browser to the selected terminal pod
• Go service that tracks which terminal pods are free, in use, or being recreated
• Go service that creates new capacity when the spare terminal pool runs out
• Container image that runs the Linux shell environment exposed to users through node-pty

The most notable aspect is the project’s terminal manager written in Go, pseudo-terminal-manager, which allocates and exposes backend terminal instances programmatically via the Kubernetes API.

Read the full Webterm write-up here for more details.