Add pets vs cattle explanation

slides/containers/First_Containers.md

@@ -203,4 +203,90 @@ bash: figlet: command not found
 
 * The basic Ubuntu image was used, and `figlet` is not here.
 
-* We will see in the next chapters how to bake a custom image with `figlet`.
+---
+
+## Where's my container?
+
+* Can we reuse that container that we took time to customize?
+
+  *We can, but that's not the default workflow with Docker.*
+
+* What's the default workflow, then?
+
+  *Always start with a fresh container.*
+  <br/>
+  *If we need something installed in our container, build a custom image.*
+
+* That seems complicated!
+
+  *We'll see that it's actually pretty easy!*
+
+* And what's the point?
+
+  *This puts a strong emphasis on automation and repeatability. Let's see why ...*
+
+---
+
+## Pets vs. Cattle
+
+* In the "pets vs. cattle" metaphor, there are two kinds of servers.
+
+* Pets:
+
+  * have distinctive names and unique configurations
+
+  * when they have an outage, we do everything we can to fix them
+
+* Cattle:
+
+  * have generic names (e.g. with numbers) and generic configuration
+
+  * configuration is enforced by configuration management, golden images ...
+
+  * when they have an outage, we can replace them immediately with a new server
+
+* What's the connection with Docker and containers?
+
+---
+
+## Local development environments
+
+* When we use local VMs (with e.g. VirtualBox or VMware), our workflow looks like this:
+
+  * create VM from base template (Ubuntu, CentOS...)
+
+  * install packages, set up environment
+
+  * work on project
+
+  * when done, shutdown VM
+
+  * next time we need to work on project, restart VM as we left it
+
+  * if we need to tweak the environment, we do it live
+
+* Over time, the VM configuration evolves, diverges.
+
+* We don't have a clean, reliable, deterministic way to provision that environment.
+
+---
+
+## Local development with Docker
+
+* With Docker, the workflow looks like this:
+
+  * create container image with our dev environment
+
+  * run container with that image
+
+  * work on project
+
+  * when done, shutdown container
+
+  * next time we need to work on project, start a new container
+
+  * if we need to tweak the environment, we create a new image
+
+* We have a clear definition of our environment, and can share it reliably with others.
+
+* Let's see in the next chapters how to bake a custom image with `figlet`!