episode-02

Episode 2 - Containers

Date: November 25, 2020

Video URL: https://www.youtube.com/watch?v=AHDrejEv0SM

Web page for episode: https://kube101.jeffgeerling.com/2020/episode-2-containers

Outline:

• Why does Kubernetes use containers?
• How do you build a container?
• Build a simple Go app
• Run the Go app directly
• Run the Go app in a container
• Push the Go app to an image registry

Instructions for 'Hello Go' app

There is a very simple Go-based web app that responds to HTTP requests on port 8180 in cmd/hello/hello.go.

After installing Go, you can run the app directly with the command:

go run cmd/hello/hello.go

Or you can build the Go command hello binary using:

go build cmd/hello/hello.go

And then run it and monitor requests (access localhost:8180/some-path-here in a browser):

$ ./hello
2028/10/24 17:30:36 Starting webserver on :8180
2028/10/24 17:30:59 Received request for path: /some-path-here

After you're finished, you can remove the binary with rm hello.

Build the 'Hello Go' Docker container image

Next up, we want to set up a container build environment that can build the Go application and then also run it (but without all the Go language cruft) in a trimmed down container image.

There is a Dockerfile in this directory containing a multi-stage Docker build layout which first builds the Go app using the official golang Docker image, then builds the final container based on Alpine Linux (using the official alpine Docker image).

To build the container, run:

docker build -t geerlingguy/kube101-go .

Once the container is built, you can see it in your list of docker images, and you can run it with the command:

docker run --rm -p 8180:8180 geerlingguy/kube101-go

Push the container image to a private Docker registry

When you're satisfied the container image works correctly, go ahead and push it up to a Docker registry.

For my example, I'm pushing it to a private Docker Hub repository named geerlingguy/kube101-go:

docker push geerlingguy/kube101-go

Note: Pushing to a registry typically requires authentication. Please read the documentation for a guide on how to make sure you are authenticated to your Docker Hub (or other provider) account.

Also, it's likely you won't be able to push to my namespace, so you might want to try using your own namespace instead of geerlingguy ;-)