➕ Add quick intro to demo apps

slides/k8s/demo-apps.md

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+# Our demo apps
+
+- We are going to use a few demo apps for demos and labs
+
+- Let's get acquainted with them before we dive in!
+
+---
+
+## The `color` app
+
+- Image name: `jpetazzo/color`, `ghcr.io/jpetazzo/color`
+
+- Available for linux/amd64, linux/arm64, linux/arm/v7 platforms
+
+- HTTP server listening on port 80
+
+- Serves a web page with a single line of text
+
+- The background of the page is derived from the hostname
+
+  (e.g. if the hostname is `blue-xyz-123`, the background is `blue`)
+
+- The web page is "curl-friendly"
+
+  (it contains `\r` characters to hide HTML tags and declutter the output)
+
+---
+
+## The `color` app in action
+
+- Create a Deployment called `blue` using image `jpetazzo/color`
+
+- Expose that Deployment with a Service
+
+- Connect to the Service with a web browser
+
+- Connect to the Service with `curl`
+
+---
+
+## Dockercoins
+
+- App with 5 microservices:
+
+  - `worker` (runs an infinite loop connecting to the other services)
+
+  - `rng` (web service; generates random numbers)
+
+  - `hasher` (web service; computes SHA sums)
+
+  - `redis` (holds a single counter incremented by the `worker` at each loop)
+
+  - `webui` (web app; displays a graph showing the rate of increase of the counter)
+
+- Uses a mix of Node, Python, Ruby
+
+- Very simple components (approx. 50 lines of code for the most complicated one)
+
+---
+
+class: pic
+
+![Dockercoins application diagram](images/dockercoins-diagram.png)
+
+---
+
+## Deploying Dockercoins
+
+- Pre-built images available as `dockercoins/<component>:v0.1`
+
+  (e.g. `dockercoins/worker:v0.1`)
+
+- Containers "discover" each other through DNS
+
+  (e.g. worker connects to `http://hasher/`)
+
+- A Kubernetes YAML manifest is available in *the* repo
+
+---
+
+## The repository
+
+- When we refer to "the" repository, it means:
+
+  https://github.com/jpetazzo/container.training
+
+- It hosts slides, demo apps, deployment scripts...
+
+- All the sample commands, labs, etc. will assume that it's available in:
+
+  `~/container.training`
+
+- Let's clone the repo in our environment!
+
+---
+
+## Cloning the repo
+
+.lab[
+
+- There is a convenient shortcut to clone the repository:
+  ```bash
+  git clone https://container.training
+  ```
+
+]
+
+While the repository clones, fork it, star it ~~subscribe and hit the bell!~~
+
+---
+
+## Running Dockercoins
+
+- All the Kubernetes manifests are in the `k8s` subdirectory
+
+- This directory has a `dockercoins.yaml` manifest
+
+.lab[
+
+- Deploy Dockercoins:
+  ```bash
+  kubectl apply -f ~/container.training/k8s/dockercoins.yaml
+  ```
+
+]
+
+- The `webui` is exposed with a `NodePort` service
+
+- Connect to it (through the `NodePort` or `port-forward`)
+
+- Note, it might take a minute for the worker to start
+
+---
+
+## Details
+
+- If the `worker` Deployment is scaled up, the graph should go up
+
+- The `rng` Service is meant to be a bottleneck
+
+  (capping the graph to 10/second until `rng` is scaled up)
+
+- There is artificial latency in the different services
+
+  (so that the app doesn't consume CPU/RAM/network)
+
+---
+
+## More colors
+
+- The repository also contains a `rainbow.yaml` manifest
+
+- It creates three namespaces (`blue`, `green`, `red`)
+
+- In each namespace, there is an instance of the `color` app
+
+  (we can use that later to do *literal* blue-green deployment!)